microplasma displays are fl exible and transparent

www.laser focusworld.com Ju ly 2010

Scanning optics slice 3D images PAGE 48

Structured fiber advances short-pulse lasers PAGE 52

Imaging spectrometers get smaller PAGE 57

Manufacturers’ Product Showcase PAGE 71

Femtosecond amplifi er output gets a boost PAGE 39

International Resource for Technology and Applications in the Global Photonics Industry

Microplasma displays are fl exible and transparent PAGE 33

Contents | Zoom in | Zoom out Search Issue | Next PageFor navigation instructions please click here

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VAMP test data

Amplified Mode Hop Free Tuning from 765 nm to 782 nm

765 770 775 780

Wavelength (nm)

0

2

4

6

8

10

12

14

16

18

20

Inpu

t Pow

er (m

W)

P(out)P(in)

Outp

ut P

ower

Fro

m A

mpl

ifier

(W) 1.0

0.5

Previous Page | Contents | Zoom in | Zoom out | Front Cover | Search Issue | Subscribe | Next PageLaser WorldFocus BA

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JULY 2010 ■ VOL . 46, NO. 7

International Resource for Technology and Applicationsin the Global Photonics Industry

July 2010 www.laserfocusworld.com Laser Focus World 2

d e p a r t m e n t sc o l u m n s

n e w s b r e a k s w o r l d n e w s

L A S E R S ■ O P T I C S ■ D E T E C T O R S ■ I M A G I N G ■ F I B E R O P T I C S ■ I N S T R U M E N T A T I O N

13 Diode-Pumped Solid-State Lasers Modelocked Ti:sapphire

laser is pumped by blue laser diodes.

14 Metamaterials Electromagnetic ‘black hole’

is experimentally realized

16 Infrared Imaging OLED converts IR to visible:

Night vision for your cell phone?

18 Microstructured Fiber Fiber-sensor technology

is thin-skinned but robust

22 Photodetectors LWIR plasmonic detector has breakthrough

sensitivity and quantum effi ciency

24 Dye Lasers Small pulsed organic laser is highly effi cient

9

Resonant metalens resolves to λ/80

LC-fi lled PC fi bers form tunable

bandpass fi lter

Wake Forest patents low-cost, highly

effi cient plastic-optical-fi ber solar cells

10

Cold-atom gravimeter requires

only one laser beam

11

Biological protein can self-assemble into tiny

nanolasers and other photonic devices

Optical gain seen in plasmonic waveguides

7 THE EDITOR’S DESK

Material matters

Stephen G. Anderson

Associate Publisher/Chief Editor

31 BUSINESS FORUM

How can I develop my consulting business?

Milton Chang

76 IN MY VIEW

The sayings of Rear Admiral Grace Murray Hopper, USN

Jeffrey Bairstow

66 NEW PRODUCTS

71 MANUFACTURERS’ PRODUCT SHOWCASE

74 BUSINESS RESOURCE CENTER

75 ADVERTISING/WEB INDEX

75 SALES OFFICES


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3Laser Focus World www.laserfocusworld.com July 2010

f e a t u r e s

LFW on the Web Visit www.laserfocusworld.com for breaking news and Web-exclusive articles

33 COVER STORY

By successfully confi n-

ing plasmas in arrays of

microcavities, research-

ers and engineers at the

U. of Illinois have real-

ized thin, inexpensive

light-emitting sheets.

Shown is a fl exible and

transparent display

based on microplasmas

sealed within two thin

plastic sheets. (Image

courtesy of the Univer-

sity of Illinois and Eden

Park Illumination)

33 FLEXIBLE DISPLAYS

Sheetlike microplasma arrays have many applications

By shrinking plasmas to microscopic

dimensions, thin light-emitting sheets

ideally suited for displays, specialty

and general illumination, environmental

remediation, and sterilization have

become a reality.

J. Gary Eden and Sung-Jin Park

39 ULTRAFAST LASERS

Femtosecond amplifi er output gets a boost

Advanced ultrafast amplifi ers combine

high power, excellent beam quality,

and high repetition rates in a turnkey

system without cryogenic cooling.

Steve Butcher and Marco Arrigoni

48 SCANNING OPTICS

Optical-sectioning microscope uses a single-pixel detector

A programmable-array microscope

relies on a digital-micromirror device

and a sampling technique called

compressive sensing to take 2D slices

of 3D objects, all the while collecting

light with just a single detector.

John Wallace

51 FIBERS FOR FIBER LASERS

Structured fi ber advances short-pulse laser performance

Chirally coupled core fi ber enables

scaling of single-mode fi ber core size—

essential for the high-peak-power laser

operation needed in high-precision

materials processing applications.

Phill Amaya

57 MINIATURIZED IMAGING

SPECTROMETERS

Prism-based spectrometers tackle today’s miniaturization requirements

Because a prism transmits 90% of

light over an extended wavelength

range, matching it to a CCD detector

with close to 90% quantum effi ciency

creates a nearly ideal system that, with

some tradeoffs, can be miniaturized

to meet portable spectroscopy

application needs. Jeremy Lerner

61 PHOTONIC FRONTIERS:

FREQUENCY-SHIFTED

DIODE LASERS

Shifting semiconductor laser wavelengths poses challenges

Nonlinear optics can generate new

lines from semiconductor lasers by

harmonic generation and frequency

mixing, but it requires high power, good

beam quality, and narrow linewidth.

Jeff Hecht

Coming

in August

Ellipsometry characterizes thin-fi lms in the IR

Modern IR-surface ellipsometry instruments and associated data analysis software can provide accurate and repeatable thickness and optical property measurements of substrates, as well as single and multilayer fi lm samples, over a large spectral range. In this article, authors at J.A. Woollam Co. and LohnStar Optics use several real-life examples to demonstrate the versatility of ellipsometers for characterization of substrates and thin-fi lms.


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laserfocusworld.online More Features, News & Products

e x c l u s i v e f e a t u r e s e x t r a s

®

www.laserfocusworld.compowering photonics technologies & applications on

Blog: Inside the world of venture capital

Done it vs. Read about it I was having a drink with an old friend who is the best product marketing guy I know, he was also my BoD member and

an excellent operating partner at Accel. We were discussing the diffi culty in hiring the right VP Sales, VP Marketing, and, hardest of

all, VP Product Management.

http://bit.ly/

bcMr4v

Blog: Opto Insider

Time for customers to pony up There was news recently that Morgenthaler Ventures is ending its track for funding opto hardware start-up companies, mostly in silicon, but including optical components. This is not good news, to be sure, but maybe it’s time again for the systems integrators to fi nally pony up for components research.http://bit.

ly/9AWUuX

Videos

CLEO/Laser Focus World

Innovation AwardsLearn more about the technologies that make this year’s Innovation Awards winner

and honorable mentions stand out from the crowd.http://bit.ly/

cWedVu

UV DETECTORS

Zinc-oxide materials and their alloys redefi ne UV sensingZinc oxide (ZnO) and its alloy MgZnO are emerging as promising ultraviolet-sensing candidates due to their direct wide bandgap (wider than aluminum gallium nitride) and the ability to tailor their electronic, magnetic, and optical properties through doping and alloying. Shiva Hullavarad and Nilima Hullavarad

http://bit.ly/9bsLOk

PRODUCT FOCUS: OPTICAL SPECTRUM ANALYZERS

Understanding the latest features in optical spectrum analyzersAn OSA has long been an important tool for signal discrimination in

networking. New capabilities such as in-band OSNR and wider dynamic range are expanding their potential in next-gen networks and extending them to other applications. Valerie C. Coffey

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CLEO 2010 Rocks!The 2010 CLEO Conference on Lasers and Electro-Optics (CLEO) celebrated the 50th Anniversary of the Laser with special displays, events, plenary and technical sessions, and an outstanding LasersRock! celebration.http://bit.ly/9waAL6

Visit our web siteFind in-depth news and features, as well as photonics products at our newly redesigned web site featuring topic centers on biophotonics, instrumentation, imaging and detectors, and more.www.laserfocusworld.com

Post your video! Send file to: [email protected]


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editor’s desk

Christine A. Shaw Senior Vice President & Group Publisher,

(603) 891-9178; [email protected]

Stephen G. Anderson Assoc. Publisher/Editor in Chief, (603) 891-9320; [email protected]

Gail Overton Senior Editor, (603) 305-4756; [email protected]

John Wallace Senior Editor, (603) 891-9228; [email protected]

Carrie Meadows Managing Editor, (603) 891-9382; [email protected]

Sharon A. MacLeod Executive Assistant, (603) 891-9224; [email protected]

CONTRIBUTING EDITORS

Jeffrey Bairstow In My View, [email protected]

David A. Belforte Industrial Lasers, (508) 347-9324; [email protected]

Valerie Coffey (978) 263-4485; [email protected]

Jeff Hecht Photonic Frontiers, (617) 965-3834; [email protected]

Conard Holton Imaging, (603) 891-9161; [email protected]

D. Jason Palmer Europe, 44 (0)7960 363 308; [email protected]

Adrienne Adler Marketing Manager

Suzanne Heiser Art Director

Sheila Ward Production Manager

Chris Hipp Senior Illustrator

Diane Giannini Web Publisher

Debbie Bouley Audience Development Manager

Steve Archer Ad Services Manager

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CORPORATE OFFICERS

Frank T. Lauinger Chairman

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Audience Development and Book Publishing

Subscription inquiries

(847) 559-7520; fax (847) 291-4816

e-mail: [email protected]

web: www.lfw-subscribe.com

EDITORIAL ADVISORY BOARD

Dan Botez, University of Wisconsin-

Madison; Connie Chang-

Hasnain, UC Berkeley Center for

Opto-electronic Nanostructured

Semiconductor Technologies;

Pat Edsell, Avanex;

Jason Eichenholz, Ocean Optics;

Thomas Giallorenzi, Naval

Research Laboratory;

Ron Gibbs, Ron Gibbs Associates;

Anthony M. Johnson, Center

for Advanced Studies in Photonics

Research, University of Maryland

Baltimore County;

Kenneth Kaufmann, Hamamatsu

Corp.; Larry Marshall, Southern

Cross Venture Partners; Jan Melles,

Photonics Investments;

Masahiro Joe Nagasawa, TEM Co.

Ltd.; David Richardson, University

of Southampton; Ralph A. Rotolante,Vicon Infrared; Toby Strite, JDS

Uniphase.


Stephen G. Anderson

Associate Publisher/

Editor in Chief

[email protected]

Material mattersThe fi eld of materials processing has come a long way from the early days of blasting holes in stacks of

steel razor blades with CO2 lasers. Its advance has required research and development into both the

interaction of light with the materials involved and the design of the lasers themselves. For a light/mate-

rial interaction to be routinely successful, the laser must deliver its output at a specifi c wavelength, pow-

er, beam quality, and stability. Interest in the use of short pulses for high-precision materials processing

applications like direct structuring of components or microvia hole drilling has “raised the bar” on such

performance specifi cations, especially pulse length and repetition rates. Because of their effi ciency and

relative simplicity, fi ber lasers are particularly attractive for industrial materials processing and recent

developments in structured fi bers may help broaden their use in short-pulse applications (see page 51).

The use of short (or fast) pulses in basic science is well established, though the pulses typical in the re-

search arena are much shorter than those generally used for materials processing. But while the order of

magnitude of the pulsewidth may be different, the desire for power and beam quality coupled with pulse-

to-pulse stability and higher repetition rates is common to both markets. Ultrafast amplifi ers are one route

to higher-power femtosecond pulses, though they have traditionally been a complex option—at least one

system now offers a performance boost from a turnkey package without cryogenic cooling (see page 39).

Working with materials in a different context has led to many exciting advances in photonics, one of

which is highlighted on our cover. The emerging fi eld of microplasma

technology could lead to some novel displays and lighting. The exam-

ple shown is a fl exible and transparent display based on an array of

microplasmas sealed between two plastic sheets (see also page 33).


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newsbreaks

Resonant metalens resolves to λ/80

Researchers at the Institut Langevin, ESPCI ParisTech & CNRS

(Paris, France) have designed and created a novel form of sub-

wavelength-structured lens called a metalens, which breaks the

diffraction limit but operates in a way very different from that of

a conventional near-fi eld lens. The experimental prototype, built

for use in the microwave region (as are many fi rst attempts at

fabricating metamaterial optics), produced a far-fi eld image at a

resolution of λ/80 of an object consisting of 16 point sources.

The metalens consists of a 2D array of identical

subwavelength-sized resonators (in the prototype, they are

copper wires); the object, which is placed in the near fi eld of the

metalens, is illuminated with broadband light. The near-fi eld

energy captured by the lens decomposes into many different

spatial modes, each of which remains in the resonators for a

different length of time, with the modes with highest spatial

detail remaining the longest. The far-fi eld output is recorded

and the image reconstructed using an inversion algorithm. The

researchers plan to further increase resolution by adding some

disorder to the resonators to enhance dispersion. They believe

that metalenses can be created at visible wavelengths using

nanoparticles or nanowires as resonators. Contact Geoffroy

Lerosey at [email protected].

LC-fi lled PC fi bers form

tunable bandpass fi lter

Two short sections of optical fi ber that combine

to become an electrically tunable bandpass fi lter

have been fabricated by scientists at the Technical

University of Denmark (Lyngby, Denmark) and NKT

Photonics (Birkerød, Denmark). The 10 mm long

sections are each large-mode-area solid-core

photonic-crystal (PC) fi bers with their holes fi lled

with a fl uid of liquid-crystal (LC) molecules; the

hole diameters and the LC type are different for

each section. The two sections are placed serially

and butt-coupled in a silicon v-groove containing

gold electrodes along the sides of the groove; two

single-mode fi bers are also held in the ends of the

groove and butt-coupled to the sections to couple

light in and out of the PC-fi ber arrangement.

Light from a supercontinuum-fi ber source is

coupled into the device. One LC type is a long-

pass fi lter and the other a shortpass fi lter; the

combination produces a bandpass fi lter trans-

mitting over the 1520 to 1680 nm range. When

a driving voltage variable between 90 and 120 V

is applied to one LC and no voltage to the other,

the shortpass edge of the fi lter can be tuned

over a 36 nm bandwidth, with the longpass

edge immobile. A similar process applied con-

versely to the fi ber sections produces a longpass

tuning range of 12 nm with no shortpass change.

Contact Lei Wei at [email protected].

Wake Forest patents low-cost, highly

effi cient plastic-optical-fi ber solar cells

A new type of potentially low-cost solar cell that is twice as effi cient as tra-

ditional organic solar cells—and may even rival silicon fl at-panel cells—has

been patented by research professors in the Center for Nanotechnology and

Molecular Materials at Wake Forest University (Winston-Salem, NC). Fiber-

Cell, a Winston-Salem spinoff of the nanotechnology center, has already li-

censed the technology for commercialization and has successfully fabricated

lightweight and fl exible solar-cell modules using inexpensive roll-to-roll and

spray-on techniques.

The solar cell is made

using millions of tiny

plastic optical fi bers

that collect light at

oblique angles, prolong-

ing the effi cient collec-

tion of sunlight from

early morning through

evening hours. The fi ber

structure is composed

of polymethylmethacry-

late or perfl uorocyclobu-

tyl aligned optical fi bers followed by an interior indium tin oxide (ITO)-based

transparent conductor layer and a polythiophene:butyric acid methyl ester ab-

sorptive cladding layer. An aluminum external refl ector and contact along the

outside of the fi bers funnels incoming light down the fi ber, where photons

are absorbed by the cladding layer and converted to electrons. Prototype 10

× 10 cm solar panels have been fabricated and are now undergoing testing at

other laboratories. Contact David Carroll at [email protected].


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π/2

π

π/2

Interferometerduring free fall

3D pyramidalmagneto-optic trap

Raman 1

Raman2

Coils

Detection

newsbreaks

NEWS ONLINESee more breaking news at

www.laserfocusworld.com

Cold-atom gravimeter requires only one laser beamAtom interferometers used as sensitive gravimeters (which de-

tect the strength of the local gravity fi eld, or g) are normally

quite complex, requiring nine independent laser beams and

associated optics, making them too cumbersome to use in the

fi eld. Researchers at LYN-SYRTE, UPMC (Paris, France) have

created a cold-atom gravimeter based on Raman transitions

that requires only one laser beam and is very compact. The

device relies on a 3D hollow pyramidal magneto-optic trap

(MOT) to trap the atoms; the four inner mirrors of the trap

also produce the proper polarizations to drive the Raman tran-

sitions and measure the positions of the falling atoms.

The MOT, which is custom-made from two glass corner

cubes and two glass isosceles rectangular prisms, has a 20 × 20

mm pyramid base and mirror faces that are perpendicular to

each other to within one arc minute. Two laser diodes are tuned

to frequencies close enough to correspond to the microwave

transition of the ground levels of rubidium (Rb). The combined

collimated beam enters along the axis along which the Rb at-

oms fall. Measurement of g is achieved by adjusting the Raman

frequency difference until its chirp compensates the measured

Doppler shift (which changes as the atoms fall). Measurements

taken over a 50 h span matched variations expected from the

earth’s tides, with a short-term (1 s) sensitivity of 1.7 × 10-7 g.

Contact Arnaud Landragin at [email protected].


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Laser Focus World

newsbreaks

Optical gain seen

in plasmonic

waveguides

Propagation of surface-plasmon polaritons

(SPPs) with optical gain over macroscopic

distances has been demonstrated in a collbo-

ration by the University of Iceland (Reykjavik,

Iceland), Harvard Medical School (Boston, MA),

the University of Cologne (Cologne, Germany),

and the Fraunhofer Institute for Applied Optics

and Precision Engineering (Jena, Germany).

To overcome the substantial ohmic losses

normally seen at the plasmon-dielectric inter-

face, the researchers fabricated symmetric di-

electric-metal-dielectric waveguides support-

ing coupled SPP modes on the top and bottom

interfaces of a metal fi lm. Because mode con-

fi nement and propagation loss for these long-

range SPP modes decreases with metal thick-

ness, amplifi ed spontaneous emission (ASE)

for the propagating SPPs can be observed.

The waveguides consisted of a 4 nm thick

gold layer and a 1 μm layer of a fl uorescent

poly(phenylene vinylene) derivative blended

with a large-bandgap poly(spirofl uorene) poly-

mer and an alkyl compound that were sand-

wiched between two 20 μm thick transparent

polymer layers on a silicon substrate. Experi-

ments that gradually increased 532 nm pump

power to the waveguide produced ASE near

600 nm. The measured net optical gain was

8 cm-1, which corresponds to a 3000-fold sig-

nal increase after 1 cm of propagation. Con-

tact Malte C. Gather at [email protected].

Biological protein can self-assemble into tiny nanolasers and other photonic devices

Found in the cells of nearly every living thing,

the protein clathrin forms into tripod-shaped

subunits called triskelia that sort and transport

chemicals into cells by folding around them.

While multiple triskelia can self-assemble into

cage structures with 20 to 100 nm diameters for

applications in drug delivery and disease target-

ing, scientists at ExQor Technologies (Boston,

MA) see a host of other nanoscale electronic

and photonic applications for clathrin that could

rival those for silicon or other inorganic devices,

including a bio-nanolaser as small as 25 nm.

A spherical scaffold of clathrin subunits forms

ExQor’s patented clathrin bio-nanolaser. How

can a chromophore so small (25 to 50 nm in size)

serve as a cavity for visible light? ExQor says it

forces chromophore-microcavity interaction, and

this combination possesses a high-enough Q for

lasing. In this way, the bio-nanolaser produces

self-generated power in a sub-100-nm diameter

structure for potential applications in illuminating

and identifying (or possibly destroying) particular

biological tissues by functionalizing the structure

with antibodies or other agents that can target

particular pathogens or even certain cells. In ad-

dition, ExQor says quantum-mechanical effects

could be used that might enable unique, spin-

based, self-assembling nanoelectronic/nano-

photonic devices and even bio-based quantum

computers composed of clathrin protein. Contact

Franco Vitaliano at [email protected].


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Improving the quality of light

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HR, ROC =100 mm

Ti:Al2O3crystal

Fused silicaprisms Slit Output

TocHR,ROC = 75 mm

HR: High reflector ROC: Radius of curvature SBR: Saturable Bragg reflector

HR/SBR

GaN diode laser

1 W, 452 nm

world newsTechnical advances from around the globe

Got News? Please send articles to [email protected]


plasmonic

detector

See page 22

Although titanium-doped sapphire is a versatile laser gain ma-

terial and the main ingredient in widely tunable and ultrafast

Ti:sapphire lasers used across a broad spectrum of photonic ap-

plications, it requires a high-brightness (bulky and expensive)

pump source—typically, a multiwatt argon-ion or frequency-

doubled neodymium laser. Now, increased power levels for gal-

lium nitride (GaN)-based blue and green laser diodes have en-

abled researchers at the University of Strathclyde’s Institute of

Photonics (Glasgow, Scotland) to be the fi rst to demonstrate a

modelocked Ti:sapphire laser directly pumped by a laser diode.1

An unlikely result

Because the optical power of blue and green laser diodes is gen-

erally low and their wavelength is poorly matched to the broad,

but weak absorption spectrum of the Ti:sapphire gain material,

the laser industry has always felt that diode-pumped Ti:sapphire

was an unlikely achievement. Nonetheless, a compact 1 W, 452

nm GaN laser diode from Nichia (Tokushima, Japan) is suffi cient

for a Ti:sapphire laser with a continuous-wave output of 19 mW

at 800 nm in a standard cavity (see fi gure).

To achieve lasing, an aspherical collimating lens, a two-el-

ement cylindrical-lens telescope, and a spherical focusing

lens were used to concentrate the laser-diode output onto a

Ti:sapphire crystal within a four-mirror cavity. The calculated

cavity-waist radius was 25 × 15 μm in the crystal. For an output

coupling of 0.5%, a modelocking threshold of 750 mW and a

maximum average output power of 9 mW were obtained with

870 mW incident on the crystal. Using interferometric autocor-

relation, the transform-limited output had a measured full-width

half-maximum pulsewidth of 116 fs.

Challenges remain

The measured output power was lower than predicted by mod-

eling. The researchers say this is due to pump-induced losses at

the lasing wavelength; however, the losses are not observed at

wavelengths above 477 nm. Because progress has been made in

longer-wavelength GaN laser diodes, the team is confi dent that

future experiments will soon produce a higher-output-power di-

rect-diode-pumped Ti:sapphire laser. Even using the current laser

diode at 452 nm along with double-sided pumping or polariza-

tion-combining techniques, the research team is confi dent that

output powers around 50 mW could be achieved.

“Diode-laser-pumping of Ti:sapphire enables drastic reductions

in complexity over current systems,” says PhD student Peter

Roth. “As a result, some of the unrivaled performance of today’s

high-cost tabletop Ti:sapphire lasers may soon be available at a

fraction of the current cost and footprint. With currently avail-

able GaN diode lasers [approximately 1 W per device around

450 nm], a tunable femtosecond Ti:sapphire laser with an aver-

age output power of roughly 50 mW should be possible by mul-

tiplexing two diodes... Such a laser would fi nd numerous applica-

tions from imaging to spectroscopy—for example, as a bolt-on

accessory to a fl uorescence microscope.” —Gail Overton

REFERENCE

1. P.W. Roth et al., “Modelocking of a diode-laser-pumped Ti:sapphire la-

ser,” CLEO 2010, paper CMNN1, San Jose, CA.

Commercially available blue laser diodes from Nichia (top right) are

used in a compact setup (lower diagram) for the fi rst time as a low-

cost pump source for a Ti:sapphire laser in place of conventional

bulky and higher-cost frequency doubled solid-state lasers (top left).

(Courtesy of the University of Strathclyde)

Modelocked Ti:sapphire laser is pumped by blue laser diodes

D I O D E - P U M P E D S O L I D - S T A T E L A S E R S


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world news

Electromagnetic ‘black hole’ is experimentally realizedThe subwavelength structure of optical

metamaterials gives them their unique

properties—and also makes them chal-

lenging to fabricate. This is why meta-

materials researchers sometimes fi rst

opt to put their ideas into practice in the

microwave region, which brings the size

of a structure’s unit cell up from a few

hundred nanometers to a few millime-

ters. Once proven with microwaves, the

concept can then (at least sometimes) be

scaled down into the optical regime.

Researchers at Southeast University

(Nanjing, China) have taken an idea fi rst

proposed last year and implemented it in

the microwave region.1 The idea—a meta-

material omnidirectional optical absorb-

er, or electromagnetic “black hole”—was

fi rst proposed last year; if ultimately cre-

ated in the optical region, the device could

be useful for maximizing the light absorp-

tion of solar cells and photodetectors.2

Radially varying

permittivity

The experimental mi-

crowave device is 2D for

simplicity (see Fig. 1). Its

overall effect is that of

a dielectric cylinder with

a lossy inner core and a

lossless circular shell with

a permittivity that varies with radius. All

electromagnetic waves of any polariza-

tion at the design frequency that hit the

cylinder, even at a glancing angle, are

captured and spiral inward to the core.

As in many microwave metamaterial

structures, the unit cells consist of piec-

es of circuit-board material with specifi c

metal shapes etched onto them. To create

a radially varying permittivity, the metal

shapes are changed as a function of radius.

For example, the shapes could be circular

rings, “I” shapes, or Jerusalem crosses; the

dimensions of the individual shapes can

be varied as well. The researchers chose a

non-resonant I shape for the outer shell of

the absorber, and an electric-fi eld-coupled

(ELC) resonator for the inner core.

A microwave frequency of 18 GHz was

chosen for the experiments. The unit cells

were 1.8 mm in size, or about 1/10 the

M E T A M A T E R I A L S

FIGURE 1. A 2D metamaterial omnidirectional absorber of

microwave radiation, or “black hole,” is made of concentric dielectric

sheets containing different metal patterns, one type for the core

and another for the outer shell. (Courtesy of Southeast University)


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LightMachinery www.lightmachinery.com

Pulsed CO2 LasersLightMachinery pulsed CO2

lasers have a very low cost of

operation and are built for a wide

variety of applications in precision

manufacturing and R&D.

Micro-machining, wire stripping,

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Ultra-reliable lasers andresponsive customer servce


wavelength of the radiation to be cap-

tured; the entire device had 60 concen-

tric layers, with all layers three cells high.

To fi x the layers in place, circular slots

were cut into a styrofoam board and the

layers fi t into the slots.

Dark shadows

In the experiment, a nearfi eld scanning

system measured the incident micro-

waves and what happened to them as

they entered the absorber; the scanning

system could measure a 400 mm2 area

to a resolution of 0.5 mm (the absorb-

er itself was 216 mm in diameter). For

comparison, specialized numerical soft-

ware was used to simulate the absorber

and its ability to capture microwaves.

The absorption of a simulated Gauss-

ian beam striking the absorber at nor-

mal and off-center incidences was cal-

culated to be 99.94% and 98.72%,

respectively. Experimentally, it is diffi -

cult to create a small Gaussian micro-

wave beam, so an easier-to-generate

beam was used for the experiment. The

path and behavior of the beam, which

was narrow but slightly divergent, was

mapped and shown to be similar in be-

havior to simulations; in both, the beam

is seen to enter the absorber and spiral

toward the core.

Additional simulations of the response

of the absorber to a plane wave were

made for the distributions of both the

electric fi eld and the power (see Fig. 2). A

simulation of the behavior of the absorber

when subjected to an electric fi eld radi-

ated by a nearby monopole source agreed

well with the experimental measurements

of the same arrangement; both showed a

shadow region cast by the absorber.

The researchers believe that, because

the core of the device absorbs radiation

and emits it as heat, the omnidirection-

al absorber could fi nd use as a thermal

emitter or a “harvester” of electromag-

netic radiation.—John Wallace

REFERENCES

1. Q. Cheng et al., New J. Phys. 12, 063006

(2010).

2. E.E. Narimanova and A.V. Kildishev, Appl.

Phys. Lett. 95, 041106 (2009).

FIGURE 2. In a simulation, the absorber

responds to a plane wave, modifying

the electric fi eld (top) and blocking the

power (second image). A simulation of the

absorber and a nearby point source (third

image) matches well with experimental

measurements (bottom). (Courtesy of

Southeast University)

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world news


OLED converts IR to visible: Night vision for your cell phone?Optical upconversion—the process

of converting light at one wavelength

to that of a shorter wavelength (with

“up” being higher in the frequency

spectrum)—is possible by directly

combining photodetectors with LEDs.

Unfortunately, the fabrication process

is diffi cult for inorganic or even hybrid

organic/inorganic devices and photon-

to-photon conversion effi ciencies are

very low—typically less than 1%. In

addition, fabrication is expensive, and

some alternative upconversion methods

using quantum dots as an infrared (IR)

absorber suffer from high dark currents.

But thanks to advances in organic pho-

todetectors and organic LEDs (OLEDs)

with very high external quantum ef-

fi ciencies (EQEs) on the order of 20%,

researchers at the University of Florida

(Gainesville, FL) have demonstrated a

more effi cient all-organic upconversion

device that just may make night vision

on your cell phone a possibility.1

All organic

The organic upconversion device, fab-

ricated on an indium tin oxide (ITO)

substrate with overall dimensions of

I N F R A R E D I M A G I N G

In the absence of 830 nm IR radiation (left), a 0.04 cm2 all-organic upconversion device

remains dark. But in the presence of 830 nm illumination, the all-organic device upconverts

this radiation to visible green light (right). (Courtesy of the University of Florida)


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Thermo Scientific ThermoFlex recirculating chillers combine a

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To learn more about the complete family of Thermo

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world news


0.04 cm2, consisted of a tin phthalo-

cyanine (SnPc)-based bulk heterostruc-

ture layer as a near-IR (NIR) sensitizer

and an iridium-doped biphenyl OLED

layer as a phosphorescent emitter—

one of the most effi cient OLED materi-

als in use today. In photovoltaic mode,

the EQE of the NIR sensitizer layer can

be higher than 20%, while the EQE for

the OLED emitter layer is close to 20%

(compared to typical EQE values of less

than 5% for most conventional fl uores-

cent OLEDs).

In the absence of IR radiation, the

poor-hole-transport NIR sensitizer keeps

the OLED layer in the off state. But

upon photoexcitation, photogenerated

holes are injected into the OLED layer

and recombine with electrons injected

from a cathode layer to emit visible light.

The 100 nm thick NIR sensitizer layer

or fi lm has strong NIR absorption up to

1000 nm, with a peak at 740 nm. Using

an 830 nm, 14.1 mW/cm2 NIR source,

green light emission began at 2.7 V and

reached a luminance of 853 cd/m2 at

15 V. At 12.7 V, the on/off ratio of lu-

minescence intensity was about 1400

(see fi gure).

Even though maximum photon-to-

photon conversion effi ciency was only

2.7% for this device, the researchers

say that this value represents an or-

der-of-magnitude increase compared

to conventional (and more expensive

and complicated) hybrid organic/inor-

ganic devices. “Since OLEDs are be-

ing used for fl at-panel displays, the

costs of making these organic devices

are expected to be low because they

can use the existing OLED manufac-

turing infrastructure,” says Franky So,

associate professor of materials sci-

ence and engineering at the Universi-

ty of Florida.—Gail Overton

REFERENCE

1. D.Y. Kim et al., Adv. Mat. 22, 1–4 (2010).

Fiber-sensor technology is thin-skinned but robustProgress continues apace for a European

project aiming to create a fully integrated

photonic sensing “skin” that can be used

anywhere that requires close monitor-

ing of mechanical properties. The three-

year European Commission-funded proj-

ect, known as “photonic skins for optical

sensing” (PHOSFOS), has now perfected

its fi ber-production methods and has its

sights set largely on medical applications.

The 2.5-million-Euro PHOSFOS project is

being led by Francis Berghmans of the Free

University Brussels in Belgium, in collabora-

tion with a number of European universities

and the nanotechnology fi rm IMEC (Leu-

ven, Belgium). At the project’s heart is the

M ICROST RUCT U R ED F I BER


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inc.800-697-6782

world news


use of fi ber Bragg gratings created in silica

fi bers, microstructured fi bers, or exotic

plastic optical fi bers. Those in turn are to be

embedded in a thin foil or skin which the

team envisions could be put to uses rang-

ing from dentistry to civil engineering.

Key to the whole enterprise, Berghmans

says, is the integration of the elements—

the ability to integrate the optical sensing

functionality with on-board signal pro-

cessing, a power source, and even wireless

communication inside the fl exible poly-

mer skin. The skin can then be tacked to,

wrapped around, or built into any shape

the application requires.

“There are other ways to do it but not

in such an integrated manner,” he says.

“You’re getting your complete system

inside a fl exible material that can be at-

tached to anything you would like. It’s ap-

plicable in many different cases, whether

you’re thinking of medical applications or

of structural health monitoring—since ev-

erything is embedded and comes in a sin-

gle system, you’re not limited.”

The idea for PHOSFOS came from a

longstanding collaboration. “We were

working with microstructured fi bers and

had collaborations with the University

of Ghent and IMEC,” Berghmans says.

“They had the microsystems technology,

thinning diodes down until they were fl ex-

ible. We said it would be great if we could

combine everything to achieve these fully

fl edged integrated sensor systems.”

A PHOSFOS photonic-crystal fi ber (shown

here as a preform) will be patterned with

Bragg gratings and be embedded in a

fl exible polymer skin for sensing (top). An

experimental polymer skin, illuminated

with a supercontinuum source, is wrapped

around a surface to be monitored (bottom).

(Courtesy of Vrije Universiteit Brussel)


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Insensitive to temperature

But making fi ber Bragg gratings in a num-

ber of types of fi bers while maintaining

optical performance wasn’t—and still

isn’t—a straightforward business. One

principal problem was limiting the tem-

perature sensitivity of the photonic skins;

they should measure the same mechanical

properties regardless of the ambient tem-

perature. Berghmans is somewhat guard-

ed about the secret but says that the team

now has fi bers with a temperature sensi-

tivity so low as to be unmeasurable.

“You have to take advantage of the

thermal properties of the polymer fi ber;

normally these things are quite sensitive

to temperature, but if you thermally treat

them in a proper way, you can achieve

writing multiplex gratings.”

Most recently, the team pulled off a

landmark result: fi ber Bragg gratings with

features smaller than ever before, made

point by point with an ultrafast near-IR

laser.1 Each period of the grating is made

with a single pulse, and the grating is built

up by translating the fi ber through the fo-

cused spot. The team’s method is simple—

their optical setup doesn’t even attempt to

account for the curvature of the fi ber, for

instance—so it bodes well for large-scale

manufacturing in the future.

For now, the team is working to make

the production of the fi bers reliable and

repeatable. The European-funded part of

the project fi nishes early next year and

potential uses for the skins are already

mounting up.

“The killer applications are defi nitely

in the medical fi eld,” Berghmans notes.

“We’re now working toward a demon-

strator for respiratory monitoring, and

there’s another project in artifi cial limbs

or ‘smart prosthetics.’”—Jason Palmer

REFERENCE

1. T. Geernaert et al., Opt. Lett. 35, p. 1647 (2010).


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world news

LWIR plasmonic detector has breakthrough sensitivity and quantum effi ciency

Building on earlier work, researchers in

the Bio-inspired Sensors and Optoelec-

tronics Laboratory (BISOL) at Northwest-

ern University (Evanston, IL) have devel-

oped a long-wavelength infrared (LWIR)

photodetector.1

The performance of this quantum-well

IR photodetector (QWIP) was enhanced

by applying surface plasmons via peri-

odic holes fabricated in a gold-foil layer

above the quantum-well structure. For

electromagnetic waves normal to the

quantum-well surface, a properly de-

signed plasmonic array forms standing

waves with a long propagation length,

producing a cavity effect that leads to

an enhanced transverse plasmonic mode

that resonates with electron intersub-

band transitions in the quantum well and

excites additional carriers to generate a

strong photocurrent.

Designing the plasmonic array

Because photodetection is only en-

hanced if the wave-generating surface

plasmons are perpendicular to the sur-

face (due to the intersubband-polariza-

tion selection rule), 3D fi nite-difference

time-domain modeling was used to op-

timize the surface-plasmon waves and

electric-fi eld distribution. By optimizing

the surface-normal component of the

electric-fi eld intensity distribution at 8

μm (the desired operation wavelength

of the LWIR detector), the parameters

of the plasmonic array could be deter-

mined. Holes with 1.4 μm diameter in

a lattice with a 2.9 μm lattice constant

were fabricated in a 40 nm thick gold-

fi lm layer using focused ion beam (FIB)

milling over the semiconductor structure

(see fi gure). This gold layer could also be

fabricated over large areas using super-

lens lithography.2

The quantum-well structure was de-

signed to achieve a peak absorption

wavelength of 8 μm with a bound-to-

continuum transition. The indium phos-

phide/indium gallium arsenide (InP/In-

GaAs) structure includes eight periods

of 5.6 nm thick In0.53Ga0.47As doped

with a 2.5 × 1017/cm3 silicon (Si) con-

centration and 50 nm thick undoped

InP quantum barriers. These quantum

wells are sandwiched between two

highly doped (1018 Si concentration)

In0.53Ga0.47As layers 40 nm thick at the

top and 500 nm thick at the bottom

that form ohmic contacts. The thinner

top layer insures maximum proximity of

the quantum-well structure to the gold

plasmonic layer fabricated on its surface.

P H O T O D E T E C T O R S

Finite-difference time-domain modeling was used to design a gold plasmonic layer (left) that

enhances photoconductivity of a long-wavelength QWIP. Scanning-electron microscopy

shows the actual plasmonic layer as a series of holes fabricated in a gold layer (right).

(Courtesy of Northwestern University)


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Enhanced sensitivity

Analysis of the enhancement ratio of the

electromagnetic fi eld for a QWIP struc-

ture with and without the plasmonic layer

shows that this layer enhances the fi eld

by a factor of fi ve. Peak responsivity of

the device occurs at approximately 8.06

μm and is as high as 7 A/W for IR light

at normal incidence to the detector sur-

face. Because of the strong plasmonic en-

hancement of the electric fi eld, the mea-

sured peak detectivity of approximately

7.4 × 1010 cm Hz1/2/W is a few times

higher than for other InP/In0.53Ga0.47As

devices operating at a similar wavelength

and temperature. In addition, the full-

width half-maximum (FWHM) of the ab-

sorption spectrum is approximately 0.84

μm, almost half that of identical quan-

tum-well-only structures without the

plasmonic layer.

The researchers surmise that this nar-

row spectral response is due to strong

modulation of the QWIP structure by

the surface-plasmon resonance of the

gold array holes. While a narrow spec-

trum is favorable to applications that

require high spectral resolution, it is less

favorable for broadband detection.

Northwestern University associ-

ate professor Hooman Mohseni says,

“Our plasmonic layer is a perfect match

for QWIP, since it addresses the main

drawbacks of this technology. Not only

does it address the low quantum ef-

fi ciency of QWIP by enhancing the

fi eld intensity, but it also eliminates the

natural insensitivity of a QWIP to the

normal incident light.” Lead author Wei

Wu adds, “Interestingly, our plasmonic

design also performs as an antirefl ec-

tive coating, and we have plans to cre-

ate new devices over a broader spectral

range.”—Gail Overton

REFERENCES

1 . W. Wu et al., Appl. Phys. Lett. 96, 161107

(May 2010).

2. W. Wu et al., Nanotech. 18, 485302 (2007).

Small pulsed organic laser is highly effi cient

An organic optically pumped solid-state

laser called a vertical external-cavity sur-

face-emitting organic laser (VECSOL), de-

veloped by scientists at the Laboratoire

de Physique des Lasers at Université Paris

(Villetaneuse, France), produces a high-

quality beam at a conversion effi ciency

of 43%, and also is tunable.1 With further

development, the dye laser could be of

practical use for sensing or communica-

tions over plastic optical fi bers.

The gain medium is an organic poly-

methyl methacrylate (PMMA) fi lm doped

with Rhodamine 640 to 1% by weight

and spun-cast onto a fl at mirror to a

thickness of a few microns. The fl at mirror

has a refl ectivity greater than 99.5% for

D Y E L A S E R S


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wavelengths between 600 and 660 nm;

a concave (200 mm radius of curvature)

output-coupler mirror with a refl ectiv-

ity of 98% between 600 and 880 mm is

placed 4 mm away from the fl at mirror to

complete the laser cavity.

The two mirrors are transparent to light

at 532 nm, which is the pump wave-

length. The PMMA fi lm, however, ab-

sorbs 80% of the pump light in a single

pass when cast at a 17 μm thickness. The

VECSOL is pumped by a frequency-dou-

bled Nd:YAG laser beam emitting either a

“long pulse” of 7 ns duration, or a “short

pulse” of 0.5 ns duration, both with a 10

Hz repetition rate and a pump-beam di-

ameter of 140 μm (see fi gure).

Serendipitous tunability

For long-pulse pumping, the VECSOL

shows a lasing threshold of 1.8 μJ, a maxi-

mum output energy of 6 μJ (870 W peak

power), and an optical-to-optical effi ciency

of 43% (a quantum effi ciency of 63%). The

emission, which is linearly polarized in the

direction of the pump beam and is diffrac-

tion-limited (beam quality M2 of 1.0), is cen-

tered at a wavelength of about 655 nm but

consists of several peaks between 640 and

670 nm spaced by 7.5 μm—which is the

free spectral range of the Fabry-Perot etalon

formed by the thickness of the PMMA fi lm.

A VECSOL with a plano-concave resonator is pumped at 523 nm and emits at around 650

nm with a conversion effi ciency of 43%. (Courtesy of S. Forget, Laboratoire de Physique des

Lasers, CNRS/Université Paris 13)


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As a result of the spin-casting, the PMMA fi lm ended up with a vari-

ation in thickness across the mirror; this allows the laser to be tuned

over a 20 nm range by laterally translating the mirror.

The researchers also tested PMMA thicknesses of 10, 5.6,

and 2.35 μm. They observed the expected variation in peak

spacing for the different thicknesses; the spacing for the thin-

nest fi lm was large enough that the laser produced only a single

peak (although the single peak was not tunable because the

thinnest coating had a uniform thickness).

Short-pulse pumping produced a threshold of 0.95 μJ, a max-

imum output energy of 0.7 μJ (2 kW peak power), and a con-

version effi ciency of 6.3%.

The researchers note that the cavity length for the VECSOL

can be increased to 60 mm for long-pulse pumping and 10 mm

for short-pulse pumping, allowing experimenters to insert intra-

cavity optics.

“This laser could be interesting for applications which require

a cheap, compact, easy-to-handle tunable source in the visible

range,” says Sebastien Chénais, one of the researchers. “The

key difference between the VECSOL and distributed-feedback

organic lasers or organic microcavity lasers is the perfect diffrac-

tion-limited beam quality and the very high conversion effi cien-

cies that are attainable. The beam can for instance be coupled

easily to a polymer optical fi ber, whose transmission is maxi-

mum around 650 nm, which corresponds to the wavelength

range of our laser. This could then be used for short-haul data

communications. Another potential application is spectroscopy

of organic molecules, including biological systems, or chemical

sensing. It could then replace expensive and bulky optical para-

metric oscillators or liquid dye lasers in those fi elds where mod-

est energies in a pulsed mode are required.”

Chénais believes that, provided some improvements are

made to the VECSOL (for example, adding well-controlled

wavelength tunability), it could be of interest to industry. The

cost of the whole system is now approximately the cost of the

pump laser, he notes; with a cheaper pump source such as a

laser diode, the device can become cost-effective.

Easily recoated

“The ultimate goal would be the achievement of electrical pumping

with an organic semiconductor as the gain medium, but this per-

spective is today still a big challenge for the community and cannot

be regarded as realistic within a short-term period,” says Chénais.

“The limitation brought about by the inherent low photostability of

organic dyes is highly reduced compared to solid-state dye lasers

using bulk dye-doped polymer blocks (or compared to other more

complex structures that require a patterning of the active medium),

since here it takes only a few minutes to rinse the mirror and coat it

with a fresh active layer.”—John Wallace

REFERENCE

1. H. Rabbani-Haghhighi et al., Opt. Lett. 35, 12, p. 1968 (2010).


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BusinessForum

MILTON CHANG is founder and managing director of Incubic Management LLC. He is also director of Precision Photonics and mBio. Chang is a Fellow of IEEE, OSA, and LIA. He has received Distinguished Alumni awards from the University of Illinois and Caltech, is a trustee of Caltech, and is member of the Committee of 100. Contact Chang at [email protected] with questions, and visit www.incubic.com for other articles he has written regarding entrepreneurship.

Q

QA

A

I have been working on and off as a

consultant for a couple of compa-

nies since I lost my job almost two

years ago. Despite my extensive

project management experience

and reputation in the photonics

industry, I am unable to fi nd any

work recently. Any suggestions?

You may want to brand yourself as a

contractor instead of a consultant to

at least get a block of days at one time.

To many people, “consultant” implies a

high billing rate and intention to work

only sporadically—both of which are

not really the case. And given that we

are just coming out of a severe reces-

sion, companies are more likely to hire

temporary workers than permanent

employees to avoid increasing their

overhead costs just in case there is a

double dip in the economy. Also, it is

unlikely that companies will aggres-

sively pursue new projects that require

consultants at this point of the recovery.

You have to increase the number

of clients and get beyond the photo-

nics industry in order to get a stable

income and feel less impact from eco-

nomic cycles. Given the usefulness of

photonics, you should be able to fi nd

companies that want to apply photo-

nics but need your help.

You could first leverage your

reputation and the network of people

who are aware of your capability and

reputation. Generate a target list and

let your friends know your availability

and predicament. You can also

prospect broadly and promote your

credentials: Develop a web site and come up with ways for search engines to

fi nd you, attend conferences to renew acquaintances, talk to companies on the

exhibition fl oor, and even spend a few dollars to run an ad campaign (such as

using Google AdWords) for potential clients to fi nd you.

One other tactic that may be worth considering is to promote your exper-

tise and name recognition to help companies win contracts. You can boost the

likelihood of winning contracts by participating in writing proposals and by

lending your name to give the proposal more pizzazz. By getting written into

contracts, you are assured of work when the contract is awarded.

I would you like to discuss how to start a company to commercialize

my solar energy invention that I plan to patent.

In order to succeed, you must fi rst put in place all the necessary ingredients

for building a successful enterprise: technology, application, business model,

human and fi nancial resources… as well as leadership and management skills.

Having a patent is a good starting point but is no guarantee that the idea is

useful or the technology works.

Solar energy is a “hot area,” which also means risk increases exponentially

with time to market. What you don’t want to do is raise lots of money to try

to build out the company quickly to gain “fi rst mover” advantage. That is in

essence putting the cart before the horse, betting on a wing and a prayer, etc.,

that your assumptions are correct—a risky proposition, based on VC statistics,

with less than a 50/50 chance that you might succeed.

Now I will stick my neck out a bit to suggest what you might do. Work toward

an early acquisition by focusing resources to verify what a potential acquirer

might want to ascertain: The technology works, the product is manufacturable,

and customers want the product. Getting acquired is not easy but at least you

will be spending less to fi nd out earlier whether your idea is valuable. Adding a

feature to the product line of an established company could provide a competi-

tive advantage, and you may get a high valuation if several companies compete

for the ownership of your IP. And taking this approach does not deprive you

the opportunity to “go for it” if you fi nd your invention is a barnburner.

M I LT O N C H A N G

How can I develop my consulting business?


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Sheetlike microplasma arrays have many applicationsJ. GARY EDEN and SUNG-JIN PARK

Plasma, also known as the fourth

state of matter, is a partially ionized

gas or vapor. Commercial applications

of plasmas include water purifi cation,

manufacturing of integrated circuits,

and curing polymers, but of all the in-

dustrial and residential uses of plasma,

displays and lighting are pre-eminent.

The rise of fl at-panel plasma TVs in the

past decade has been nothing short of

meteoric. However, despite the recent

emphasis by manufacturers on

decreasing the power consumption

and thickness of plasma and liquid-

crystal-display (LCD) TVs, the most

pressing long-term drivers of display

development continue to be dramatic

reductions in weight

and manufacturing

cost, as well as the

introduction of

fl exibility. The avail-

ability of an economi-

cal sheetlike fl exible

display that could be

hung on a wall, or wrapped around

curved surfaces, would allow video dis-

plays to be placed virtually anywhere

for a variety of applications.

In the realm of lighting, plasma

lamps have a dominant position by

generating several gigawatts of visible

light on a continuous basis worldwide,

or approximately 80% of all the light

produced by general illumination.

Although existing plasma lamps

boast favorable effi ciencies, virtually

all contain mercury and most

require ballast and have a fragile

glass envelope. The availability of a

thin, lightweight, inexpensive, and

nontoxic source of white light would

transform the landscape of residential

and commercial lighting.

Microcavity arrays

The emerging fi eld of microplasma

technology holds considerable promise

for the next generation of displays and

lighting. By shrinking a conventional

plasma lamp by three orders of

magnitude, microscopic plasmas

having the form of cylinders, ellipsoids,

or other shapes can be generated by the

thousands or millions in microcavities

By shrinking plasmas to microscopic

dimensions, thin light-emitting sheets

ideally suited for displays, specialty and

general illumination, environmental

remediation, and sterilization have

become a reality.

FIGURE 1. 20,000 microcavities

each have a parabolic shape

and green phosphor deposited

within the cavity (left top and

bottom). A 6 × 6 in. white

lamp has a thickness of a few

millimeters (top right). A small

array of microplasmas creates

UV emission from ordinary room

air (bottom right). (Courtesy of

the University of Illinois and Eden

Park Illumination)

FLEXIBLE DISPLAYS

CO

VE

R S

TO

RY


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fabricated in the surface of glass, aluminum (Al) foil, or even

plastic. Having sizes on the order of the diameter of a human hair,

these microcavities are built by processes largely developed by

the very-large-scale-integration (VLSI) and MEMs communities.

By successfully confi ning plasmas in arrays of microcavities,

researchers and engineers at the University of Illinois have

realized light-emitting sheets that are thin and inexpensive

and, in several instances, fl exible as well. At the heart of a

microplasma device is the microcavity itself, whose shape, in

addition to the surrounding materials determines the spatial

profi le of the electric fi eld within the cavity. Most of the micro-

plasma devices being pursued today are cylindrical with diam-

eters of 50 to 200 μm, but other cross-sectional shapes such as

diamond, rectangular, and pyramidal have also been created

and used successfully, and the smallest plasmas realized to date

were confi ned to cavities 5 μm in width.

A wide array of substrate materials, including silicon, glass,

high-k ceramics, polymers, and Al have been explored. After

sealing the device (or a large array of devices) with a window

material, a gas or mixture of gases is introduced to the cavity.

With proper design of the electrodes, the dielectric separating

them, and the cavity, a stable and bright glow discharge is

produced in the microcavity when a voltage (AC, DC, or pulsed)

is applied to the electrodes.


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Near-atmospheric pressure

Although in some ways similar to

plasmas in standard fl uorescent lamps,

microplasmas have several startling

properties. Because of their small cavity

dimensions, microplasma devices oper-

ate well at pressures of roughly one at-

mosphere, as opposed to the several

thousandths of an atmosphere that is

characteristic of fl uorescent lamps. This

property is valuable for several reasons,

one of which is that little or no pressure

differential exists across the window and

substrate of a microplasma lamp, thereby

allowing the overall package to be quite

thin and fl exible. A less obvious advan-

tage is the ability to produce effi ciently, in

large numbers and in situ, transient light-

emitting molecules not normally found in

nature (such as excited diatomic xenon or

argon deuteride).

Another surprising characteristic of

microplasmas is the steady-state power

loading, or power density (electrical power

deposited in the plasma per unit volume),

which often reaches tens of kilowatts

per cubic centimeter; values as high as 1

MW/cm3 have been realized. Such excita-

tion levels are extraordinary and, in fact,

unprecedented for continuous operation of

macroscopic plasmas. For comparison, the

power loading of fl uorescent lamp plasmas

is typically tens to hundreds of milliwatts

per cubic centimeter.

To meet the need for inexpensive,

large-area display and lamp technology,

arrays of microplasma devices built into

Al foil were fi rst tested successfully four

years ago at the University of Illinois;

the development curve has been steep

ever since. Aside from the low cost of

Al foil itself, a strong attraction of this

technology is the automatic formation of

array electrodes and interconnects by a

wet chemical process.

Beginning with a single sheet of Al foil

having a thickness of nominally 120 μm,

holes or cavities 30 to 200 μm in diameter

are produced in the foil in the desired

pattern by etching. In a subsequent

electrochemical process, virtually all of

the Al in the original foil is converted into

translucent, nanoporous Al oxide (Al2O3).

This carefully controlled wet process

forms electrodes around the microcav-

ities and the electrical interconnects

between microcavities while simultane-

ously burying the microplasma devices

in a thin layer of Al2O3.

Converting aluminum to alumina

If the cavity-to-cavity spacing (pitch)

and chemical-processing parameters are

chosen properly, the electrodes for all

of the microcavities in a line (or a two-

dimensional pattern, if desired) are inter-

connected automatically. A modifi cation

of this process provides the ability to

precisely control the cross-sectional geom-

etry of a cavity, thereby opening the door

to shaping the electric fi eld throughout

the microplasma while also optimizing

the extraction of light from the cavity. For

example, an array of 20,000 micro-emit-

ters, each having a parabolic cross-section

and an emitting aperture of 160 μm, has

been fabricated (see Fig. 1). This array has

a radiating area of about 25 cm2 and, al-

though originally a 120 μm thick sheet of

ordinary Al foil, has been almost entirely

converted into transparent alumina. The

green luminescence from the array is the

result of injecting a commercial phosphor

into each microcavity and illuminating

the array with weak ultraviolet light.

Such arrays are the building blocks

for displays and lamps. Microplasma

lamps as large as 900 cm2 in active

(radiating) area have been built and

tested to date but development at Eden

Park Illumination is focusing on 6 × 6 in.2

(230 cm2) and 8 × 8 in.2 (400 cm2) white

lamps. Having a thickness of only a few

millimeters, these fl at lamps are powered

by plasmas produced within cavities in

a phosphor and alumina-overcoated Al

mesh. A carefully balanced mixture of

red, green, and blue phosphors converts

ultraviolet emission generated by the rare-

gas plasmas into white light. Although

optimizing the cavity design and other

aspects of the lamp’s construction is in

progress, the luminous effi cacy (optical

effi ciency, expressed in units of lumens/


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FLEXIBLE DISPLAYS cont inued

watt) of these fi rst-generation lamps

easily exceeds that of incandescent lamps,

and laboratory prototypes are yielding

effi cacies beyond 30 lumens/W.

Arrays of microplasmas are also

promising for environmental applications

such as the purifi cation of

air or ozone production. A

small array has been made

that operates continuously

in ordinary room air, for

example, a feat which is

extraordinarily challenging

with conventional

(macroscopic) plasma

technology. By producing

intense but uniform

glow discharges in air,

biological contaminants

can be destroyed and

pollutants or greenhouse

gases converted into other,

more useful forms.

It is f lexibility,

however, that may well

be the most appealing

aspect of microplasma technology.

Displays made by sealing microplasma

arrays within thin plastic sheets are

both fl exible and transparent, such as

shown in the low-resolution prototype

in Fig. 2. Cavities and gas-connecting

channels are stamped into the plastic

substrate by a process known as replica

molding; addressability of all the pixels

in such arrays has been achieved. With

this development, lightweight wall-sized

plasma TVs can be envisioned that could

ultimately lead to widespread adoption

of virtual-reality environments.

J. Gary Eden and Sung-Jin Park are profes-

sors of electrical and computer engineering at

the University of Illinois, 1406 W. Green, Urba-

na, IL 61801, and cofounders of Eden Park Il-

lumination, 903 N. Country Fair Dr., Champaign,

IL 61821; e-mail: [email protected]; www.

edenpark.com.

Tell us what you think about this article. Send an

e-mail to [email protected].

FIGURE 2. A fl exible and transparent display is based on

microplasmas sealed within two thin plastic sheets. Ultraviolet

emission produced by the plasmas excites a phosphor within

each cavity. (Courtesy of the University of Illinois and Eden

Park Illumination)


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Laser crystal

Conductive cooling

Radial thermal gradient

Pumplight


Femtosecond amplifi er output gets a boostSTEVE BUTCHER and MARCO ARRIGONI

Numerous applications in applied

physics and chemistry are driving a

demand for ultrafast amplifi ers that

deliver femtosecond pulses at higher

repetition rates and average power to

increase signal-to-noise ratios and re-

duce data acquisition times. Delivering

this performance without sacrifi cing

pulsewidth, beam quality, operation-

al simplicity, or reliability has proven

to be a challenge. Recent design im-

provements now enable a system that

yields up to 15 W of average power us-

ing only thermoelectric (TE) cooling of

the Ti:sapphire gain medium. Previous-

ly, these output power levels required

cryogenic cooling, resulting in complex

and space-consuming systems.

The need for power

The Ti:sapphire-based modelocked laser

oscillator revolutionized applications

of ultrafast lasers, simplifying access

to femtosecond pulses. A typical

Ti:sapphire oscillator delivers average

powers up to 2–4 W. At

repetition rates of 50–

100 MHz, the pulse

energy is at most a

few tens of nanojoules,

with a peak power of

about 500 kW, depending on the pulse

duration.

Many applications require much

higher pulse energy or peak power,

a need met with chirped pulse ampli-

fi cation (CPA). The oscillator pulses

are stretched, selected by an appro-

priate pulse picking device, ampli-

fi ed by several orders of magnitude

in another Ti:sapphire crystal, then

recompressed to pulsewidths almost

as short as the initial pulses.

Amplifi ed femtosecond pulses can

be used to pump one or more tunable

optical parametric amplifi ers (OPAs)

for pump-probe studies in solid-state

physics and photochemistry. They can

also be used to generate THz pulses

for imaging or spectroscopy. More

recently, the availability of amplifi ed

systems featuring carrier to envelop

phase (CEP) stabilization opened the

door to the production of attosecond

pulses at extreme UV (4–30 nm) wave-

lengths—pulses that are short enough

to study the dynamics of electrons in

atoms and molecules.

Many of these applications involve

one or more cascaded or parallel non-

linear conversion stages (parametric

Advanced ultrafast amplifi ers combine

high power, excellent beam quality, and

high repetition rates in a turnkey system

without cryogenic cooling.

FIGURE 1. End-pumping a

Ti:sapphire laser rod with a circular

pump beam creates a radial

thermal gradient that acts like a

strong spherical lens.

ULTRAFAST LASERS


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conversion or other effects) that are often

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energy, nonlinear stages in parallel.

Thermal lensing

A major technical hurdle in scaling ul-

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er is thermal lensing (distortion) in the

gain crystal. Even with laser pumping,

more than 75% of the pump power is

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Output beam characteristics using regenerative amplifi er

Regen + Power amp (1 kHz) Output power (W) M² (x) M² (y)

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is conductively cooled via its mounting surface(s). The end re-

sult is a radial thermal gradient perpendicular to the direction

of the laser beam (see Fig. 1). Even a pump power of just 10 W

and a beam waist of 50 μm, for instance, can result in a thermal

lens of more than 50 diopters. With pulsed pump lasers avail-

able at 40 W and higher, this lensing effect becomes the single

largest design challenge.

There are several ways to cool a Ti:sapphire crystal, thereby

reducing the strength of the thermal lens effect. Unfortunately, the

effectiveness of these cooling methods scales with their cost and

complexity. Passive conductive cooling is the simplest method, fol-

lowed by water cooling. These approaches are practical for pow-

ers up to 3–4 W. In higher-performance systems, the Ti:sapphire

crystal is usually cooled with a TE cooler, but until recently even

with this method the maximum average power was 7–8 W.

The ultimate approach is to use cryogenic cooling. At these

low temperatures the thermal conductivity of Ti:sapphire

increases roughly 40 times and the dependence of refractive

index on temperature drops by an order of magnitude. The net

result of these two effects is about a 400 times decrease in ther-

mal lens power between a Ti:sapphire crystal at 300 K and one

cooled to 77 K. Until now, all amplifi ers producing more than

a few watts were cooled cryogenically, with disadvantages in

terms of cost and complexity.



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Pump

Thermallensing effect

Incomingamplified IR beam

Normal beam divergence


A 15 W system

Diverse applications concur to make

highly desirable a 15 W class amplifi er

with the same simplicity and beam qual-

ity as a 3–4 W system.

We chose a hybrid design to deliver the

beam quality of a regenerative amplifi er

without the cost and complexity of cryo-

genic cooling. Specifi cally, the Coherent

Legend Duo HP uses a regenerative ampli-

fi er followed by a single-pass amplifi cation

stage, all in the same box, with TE cooling

for both Ti:sapphire crystals.

This approach is different from multi-

pass amplifi cation where the input pulses

pass about 10–15 times through the crys-

tal, with each pass at a slightly different

angle but providing some overlap with

the pump beam. Such a system is opti-

cally complex and results in beam quality

and pointing that is degraded compared

to the seed laser beam quality. In con-

trast, a regenerative amplifi er is a high-

gain laser cavity where pulses from the

seed laser are amplifi ed during numer-

ous round-trips and, upon reaching gain

saturation, are coupled out of the cav-

ity (see Fig. 2). The output beam charac-

teristics of the amplifi er are independent

of the seed laser, governed by the simple

cavity design, and produce a near-perfect

TEM00 mode with stable pointing char-

acteristics suited for downstream nonlin-

ear generation processes. The additional

single-pass power amplifi er is simple and

maintains the beam quality of the regen-

erative amplifi er.

With an integrated pump laser split

between the two Ti:sapphire crystals,

this regenerative plus single-pass ampli-

fi er can deliver more than 8 W at 1 kHz

and 12.5 W at 5 kHz. For the high aver-

age pump powers involved, thermal lens-

ing is not trivial but can be reduced to a

manageable level by using specially shaped

crystals with fl at, larger mounting surfaces

FIGURE 3. Using a single-pass amplifi er (SPA) to boost the output of the regenerative

amplifi er means thermal aberrations are only experienced once resulting in excellent beam

quality. Even just two passes would degrade the beam quality.


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0

0.2

0.4

0.6

0.8

1

1.2

0 0.5 1 1.5 2 2.5 3 3.5 4

Re

sp

on

se

36

24

12

48 dB/octave

Bessel

Time (ms)

-60

-50

-40

-30

-20

-10

0

100 Hz 1 kHz 10 kHz

12 dB/octave

24

36

48 dB/octave

Bessel

Re

sp

on

se

[d

B]

-60

-50

-40

-30

-20

-10

0

100 Hz 1 kHz 10 kHz

12 dB/octave

24

36

48 dB/octave

Frequency

Re

sp

on

se

[d

B]

Butterworth

0

0.2

0.4

0.6

0.8

1

1.2

0 0.5 1 1.5 2 2.5 3 3.5 4

Time (ms)

Re

sp

on

se

36

12

48 dB/octave

Butterworth24

Bessel and Butterworth Filters

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instead of the typical cylindrical

laser rod shape. The crystals are

then cooled through the fl at sur-

faces by TE coolers in a proprie-

tary highly conductive mount.

To boost the regenerative ampli-

fi er output to 15 W, we add a sec-

ond, external pump laser. The

optical setup of the regenerative

plus single-pass amplifi er is essen-

tially unchanged but the output

power is boosted to greater than

10 W at 1 kHz, 15 W at 5 kHz,

and 12 W at 10 kHz. With either

one or two pump laser confi gu-

rations, the one-pass fi nal ampli-

fi er stage does not affect the beam

pointing and TEM00 beam pro-

fi le that are key characteristics of a

regenerative amplifi er. Laboratory

tests show that this is an optimum

setup (see Fig. 3). Increasing the

number of passes from 1 to 2 only

modestly increases the overall out-

put power (by about 20%) but increases

the beam M2 value by nearly 100%. By

maintaining a low M2 value in a single-

pass setup, the design combines optical

simplicity and effi ciency with the ideal

beam characteristics for focusing into hol-

low fi ber cores or pumping multiple high-

energy OPAs, and eliminates the need for

complex cryogenic cooling (see Fig. 4).

Ultrafast amplifiers are usually

selected based on parameters like energy

per pulse, repetition rate, and mode

quality. As the experiments become

more complicated, turnkey reliability

and ease of use become increasingly

important. Design refi nements make it

possible to improve fl exibility and per-

formance, along with simplicity and

turnkey operation.

Steve Butcher is marketing manager for Re-

search Laser Systems and Marco Arrigoni is

director of marketing for the Scientifi c Market

at Coherent Inc., Santa Clara, CA; e-mail: steve.

[email protected], www.coherent.com.

FIGURE 4. Excellent beam quality enables higher

effi ciency and quality of nonlinear processes

like parametric amplifi cation and harmonic and

continuum generation. When an amplifi ed pulse

is focused into a sapphire plate (or hollow fi ber),

cascaded nonlinear effects create a supercontinuum

of light, shown here dispersed by natural diffraction.


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Single pixel detector

Beamsplitter

Objective

Collimatinglens

Relay lens

Illumination source

Excitation filter

Emission filter

“On” pixel “Off” pixel

DMD

Specimen


Optical-sectioning microscope uses a single-pixel detectorJOHN WALLACE, senior editor

Confocal microscopy, in which the

image of a point source is scanned

across the specimen and the collect-

ed light fi ltered by a pinhole to block

the out-of-focus light, allows a 3D

image of the specimen to be built up

point by point—a valuable property

for both science and industry. In the

latter, the technique is widely used to

image and inspect the patterns manu-

factured on semiconductor chips.

The scanning in an ordinary con-

focal microscope (CM) requires a

mechanically moving stage or other

device to move the focal spot relative

to the specimen. In contrast, a pro-

grammable-array microscope (PAM)

contains, somewhere within its optical

train, an array with pixels that can be

switched on and off in

individual sequence

to mimic a mechani-

cally scanned point of

light. The array can

be a digital-micro-

mirror device (DMD),

liquid-crystal-on-sili-

con (LCoS), or other type of 2D pro-

grammable array; such devices usually

allow scanning at kilohertz rates. A

PAM also requires a second 2D imag-

ing array precisely aligned to the fi nal

image of the programmable array.

Compressive sensing

The complexity of the PAM optical

system has led researchers at the Uni-

versity of Delaware (Newark, DE) to

simplify things by applying a tech-

nique called compressive sensing (CS),

in which many pixels on the pro-

grammable array are switched on at

the same time in different predeter-

mined patterns and all the light from

the specimen collected at once; sub-

sequent calculations derive the image

A programmable-array microscope relies

on a digital-micromirror device and a

sampling technique called compressive

sensing to take 2D slices of 3D objects,

all the while collecting light with just a

single detector.

FIGURE 1. A pixel pattern on a DMD forms a

modifi ed scrambled-block Hadamard ensemble;

black is “off” and white is “on” (left). No two

adjacent pixels are ever on at the same time

(the black areas between any two nearby pixels

are actually “off” pixels). The illumination source

for the SP-PAM is imaged onto the DMD at a

24° angle (right) so that, in the mirrors’ “on” state,

the illumination follows the optical axis, which is

normal to the DMD.

SCANNING OPTICS


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Bottom surface of the etched holes Top surface of the sample

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from the results.1 Using CS allows the

second array (the 2D imaging array) to

be eliminated and a single detector to

be used instead.

The pixel patterns for CS must be

carefully designed so that they effi -

ciently collect the data for the subse-

quent calculations; each pattern must

have no two adjacent pixels on at the

same time; and in combination the pat-

terns should include every pixel of the

array. The researchers chose to use pat-

terns called modifi ed scrambled-block

Hadamard ensembles (see Fig. 1).

Design and model

In the experimental single-pixel (SP)

PAM system, light from an incoherent

(tungsten-halogen) illumination source is

introduced to a DMD programmable array via a beamsplit-

ter and a relay lens; the illumination intensity across the ar-

ray is approximately uniform. The DMD is in turn imaged

onto the specimen via a collimating lens and a microscope

objective with 40X magnifi cation and a numerical aperture

(NA) of 0.65. Light collected from the specimen takes the

path back through the system, passing through the beam-

splitter to a single-pixel detector.

The DMD has frame rates of up to 8000 frames per sec-

ond. Each micromirror in the DMD has an off position of

-12° and an on position of 12° from the normal of the DMD;

as a result, the illumina-

tion light for the SP-PAM

is introduced at 24° from

the normal so that the mir-

rors refl ect the light at 0°

when in the “on” state.

The researchers mod-

eled a simplifi ed version

of their system with an

optical-design program

to examine the trans-

fer functions of versions

of the PAM architecture

with differing parame-

ters. They concluded that

a smaller DMD pitch (relative to the illumination wavelength)

results in a more-widespread transfer function, meaning a

narrower impulse response and thus a smaller single-pixel

illumination size on the image and better resolution. In addi-

tion, they found that the transfer functions had some so-

called blind spots, which could mean that the DMD-based

SP-PAM does not resolve some spatial-frequency components.

Discerning texture

The researchers used the SP-PAM to generate 2D optical sec-

tions of a dry-etched silicon sample (see Fig. 2). The sample

had etched holes about 8 μm deep with rough sidewalls and

FIGURE 2. Using the SP-PAM, optical cross-sections were taken of a patterned silicon

sample (drawing, top right). The sections were 2 μm apart (bottom, left to right). In addition,

a control image was taken with a CCD replacing the single detector and with all the DMD

mirrors “on” (upper left). (Courtesy of the University of Delaware)

Optical-Sectioning continued on page 55

A smaller DMD pitch

(relative to illumi-

nation wavelength)

results in a more

widespread transfer

function, a narrower

impulse response, and

a smaller single-pixel

illumination size.


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Helicalside core

Central core

Cladding

r

Λ

φ


Structured fi ber advances short-pulse laser performancePHILL AMAYA

A growing number of high-precision

materials processing applications re-

quire short-pulse lasers. Such appli-

cations include microvia hole drilling

in PCBs and fl ex circuits, semicon-

ductor memory repair, solar cell

edge isolation and thin-fi lm pattern-

ing, and sapphire substrate scribing

in LED manufacturing.1 All of them

are characterized by increasing min-

iaturization and/or relentless pressure

to reduce manufacturing costs.

Miniaturization and diminishing

feature size are the primary reasons

for using short-pulse lasers. Pulse

lengths of less than 80 ns are

typically required to mini-

mize the heat-affected zone

at the work piece and con-

sequent potential damage to

nearby components. Micron-

scale features also favor

shorter wavelengths because

these wavelengths can achieve

a smaller focused spot size.

Material absorption charac-

teristics are also a key con-

sideration in determining laser

wavelength.

In addition, as feature sizes

diminish, there are more fea-

tures to process per device

or per unit area so

laser pulse repetition

rate must increase or

manufacturing cycle

time per device will

grow. This require-

ment is amplified

when the substrate upon which fea-

tures are fabricated simultaneously

increases in size. The minimum fea-

ture dimension of a semiconduc-

tor memory chip, for example, has

fallen from 150 to 60 μm over the last

10 years. At the same time the sili-

con wafer has increased in size

from 200 to 300 mm. Hence the

possible number of features that

can be printed on a single wafer

has jumped by a factor of 14.

In this example, the reduction

in feature size has also driven

the process to adopt UV wave-

lengths for a smaller spot size. These

advances have driven laser develop-

ers to increase average output power

by a factor of 10 at the fundamental

wavelength of around 1.0 μm while

migrating the application wave-

length to 355 nm. Similar trends

are evident in other microelectron-

ics applications. Solar cell processing

is driven by increasing surface areas

and reducing processing time.

The vast majority of nanosecond-

pulse applications today are served

by diode-pumped solid-state (DPSS)

Chirally coupled core fi ber enables

scaling of single-mode fi ber core size—

essential for the high peak power laser

operation needed in high-precision

materials processing applications.

FIGURE 1. Chirally

coupled core fi ber

uses a central

guiding core with at

least one satellite

core wrapped

helically around it.

Inset photo shows

fi ber endface.

FIBERS FOR FIBER LASERS


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Helix period (mm)

Loss (dB/m)

10987

1000

100

10

1

0.1

LP31LP21LP11

LP01

LP02

Preform spinningand fiber pulling

during fabrication

Fiber preformmade with on-axiscentral core and

off-axis satellite core

Fabricated3C fiber

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lasers. The performance of these systems

refl ects more than 20 years of continu-

ous innovation and is largely unmatched

by any other laser technology. There are

signs, however, that some applications

may be advancing beyond

the practical capabilities of

DPSS lasers. Smaller spot

requirements and material

issues are driving pulse

lengths to the picosec-

ond regime, but the nec-

essary per-pulse energy

must be maintained even

as pulse repetition rates

increase. Creative solu-

tions are emerging, such

as “dual-beam” technol-

ogy where the output

from two pulsed sources

is multiplexed to deliver

twice the pulse repetition

rate. Another “hybrid”

approach is based on a

low-power, high-pulse-

repetition-rate fi ber laser

that seeds a DPSS ampli-

fi er in an approach that

splits the pulse genera-

tion work from the power

amplification. Though

these solutions are being

deployed, they do add cost

and complexity, and their

path for additional scaling

may be somewhat limited.

Fiber lasers

Among the solutions pro-

posed for a next-genera-

tion source to address

current and developing

short-pulse applications is the fi ber la-

ser. Key target specifi cations are sum-

marized in the table. Fiber lasers are

attractive for short-pulse applications

because of their high single-pass gain,

which enables simple amplifi er designs

and straightforward average power

scaling. The diffi culty comes in scal-

ing the fi ber core size for the high-peak-

power operation needed to achieve the

required pulse energy and duration.

Without core size scaling, nonlinear

optical effects cause spectral broaden-

ing and output power instabilities. Us-

ing 20 μm core double-clad fi ber (DCF),

FIGURE 2. Calculated modal loss for a specifi c 3C fi ber design

with core diameter of 35 μm shows that for a helix period of 9

mm, loss of less than 0.2 dB/m is achieved for the fundamental

LP01 mode and more than 100 dB/m for higher order modes.2

Target specs for fi ber lasers

Beam quality TEM00 (M2 <1.1)

Pulse energy 1.0 mJ (@10–100 kHz)

Pulsewidth 10 ns (10–100 ideal)

PolarizationLinear with polarization

extinction ratio ≥100:1

Spectral width <1 nm

Average power Up to 100 W

FIGURE 3. Spinning the 3C fi ber preform while it is drawn

causes the off-axis core to spiral around the central core

producing the desired helix.


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Absorbed pump power (W)

Signal power (W)

120 16080400

120

90

60

30

0

z position (mm)

Beam diameter (μm)

60 80 10040

30 W

M2 = 1.07

200

900

700

500

300

100CALL

1-800-374-6866

or VISITwww.photon-inc.com/nist

“I don’t think I

can continue

guessing about

my laser’s

performance.”

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with Photon

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beam profilers

Laser Focus World www.laserfocusworld.com

commercial fi ber lasers available today

promise up to 25 kW of peak power in

a 10 ns pulse, yielding 25 W of average

power at 100 kHz operation. This is

only one-quarter of the average pow-

er targeted in the table and about half

of what current DPSS lasers can deliv-

er. A promising solution with poten-

tial for further power scaling involves

a uniquely structured fi ber

named chirally coupled

core or 3C fi ber.2

This 3C fi ber enables

single-mode optical out-

put from fi bers with core

diameters much larger

than conventional double-

clad, large-mode-area fi ber.

Chirally coupled core fi ber

consists of a central guid-

ing fi ber core and at least

one satellite core wrapped

helically around the cen-

tral core (see Fig. 1). This

structure is designed to

selectively couple higher-

order optical modes from

the central core to the side

core, while propagating

only the fundamental LP01

mode in the central core.

Specifi cation of the appro-

priate side core parameters

and helical period results

in high loss for the modes

coupled into the side core,

which are scattered into

the cladding. This concept

can be applied to very-large-core fi ber

designs (see Fig. 2).

Fabrication of 3C fi ber is straightfor-

ward with two basic differences from

standard DCF production. Standard

DCF is drawn from a glass rod, known as

a preform, with an appropriately doped

center core. The dimensions of the pre-

form and its core are constructed so they

converge to the desired fi ber dimensions

when heated and drawn on a fi ber tower.

To make 3C fi ber the preform includes

two doped cores. One core is on the pre-

form central axis and one slightly off axis.

Next, when the fi ber is drawn it is spun.

This spinning causes the off-axis core to

spiral around the central core producing

the desired helix (see Fig. 3).

An important attribute of 3C fi ber is

that its performance does not depend

on specifi c bending. This is in contrast

to standard large-mode-area fi bers that

achieve single-mode performance by

FIGURE 4. Tests on the 3C fi ber demonstrate its slope

effi ciency (70%) and beam quality. Here the fi ber achieved

an M2 of 1.07.4

Fiber lasers are

attractive for short-pulse

applications because of

their high single-pass

gain, which enables

simple amplifi er designs

and straightforward

average power scaling.


M SaGEF


M SaGEF


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CHOPPERSTuning fork choppers are suitable

for long life dedicated applications,

OEM, built into an instrument or a

portable system.

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careful coiling to exploit the

differences in bend-induced

losses between the funda-

mental mode and higher-order

modes—a method that’s effec-

tive up to about 25 μm core

diameters. For larger core

sizes it becomes increasingly

ineffective.3 This technique

is also problematic for beam

delivery and use in fi ber com-

ponents. Since modal discrim-

ination is not a function of fi ber bending,

3C fi ber can be used effectively in coiled

or straight confi gurations with active or

passive fi bers.

Chirally coupled core fi bers with core

diameters of 35 μm have been made with

and without ytterbium (Yb3+) doped

cores for use as gain fi bers and in the

construction of passive fi ber compo-

nents. Laboratory testing of fi ber per-

formance in a MOPA (master oscillator

power amplifi er) confi guration has pro-

duced more than 100 W of average

power, with 10 ns pulses and 100 kW

peak power at 100 kHz pulse repetition

rate (see Fig. 4).4

Polarization

It is important to recognize that the larg-

est applications for short-pulse lasers re-

quire visible and UV wavelengths, so a

suitable fi ber laser source must have sta-

ble polarization output. Polarized light

from optical fi bers is typically created by

strong birefringence resulting from di-

rectionally oriented material stress. This

can be achieved with stress rods in the fi -

ber and works well for fi ber core diame-

ters of less than 10 μm. As fi ber core size

increases it becomes more diffi cult to

produce uniform stress across the larg-

er cross-section of the fi ber core, mean-

ing that achieving high polarization

contrast is also diffi cult. The resulting

polarization performance is very sensi-

tive to thermal and mechanical pertur-

bations, which creates output instability.

In contrast, 3C fi ber designs have

been developed that exploit the manu-

facturing process and fi ber structure to

produce very low birefringence fi bers.

These low-bi fi bers very faithfully

reproduce at their outputs the polariza-

tion state of the input light (see Fig. 5).

Shrinking component features and

relentless pursuit of lower manufactur-

ing costs will continue to drive demand

for higher-performance, short-pulse

lasers. Our 3C fi ber is one of the most

recent innovations that can enable lasers

to meet those demands with scalabil-

ity for further performance advances.

Larger-core single-mode fi bers offer

performance potential that extends

well beyond the trajectory of current

applications in materials processing.

Three examples where applications

focused research is already underway

using 3C fi ber are 1) directed energy

weapons, 2) laser-produced plasma

extreme UV lithography, and 3) ultra-

fast spectroscopy.

FIBERS FOR FIBER LASERS cont inued

FIGURE 5. As linearly polarized

light is launched into a 4 m

length of coiled 3C fi ber, the

polarization state of transmitted

light was monitored while the

fi ber was heated from 20° to

70°C. There was no rotation of

the polarization axis and the

polarization extinction remained

above 20 dB. This performance

was also found to be robust

under signifi cant mechanical and

thermal perturbations.


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In directed energy applications, larger fi ber cores are needed

to achieve targeted CW powers while maintaining narrow spec-

tral width with single polarization. Fiber lasers are desirable here

because of their high electrical-to-optical effi ciency, compact size,

and potential for more robust assembly. Extreme UV lithography

is moving toward high-volume semiconductor production based

on large CO2, pulsed laser sources. Research based on large-core

single-mode fi bers suggests a more effi cient, compact, and scal-

able laser source might be constructed by spectrally combining

high-power pulsed fi ber lasers.5 Finally, large-core, single-mode

fi ber is a key element in efforts to make a compact and robust

source for practical ultrafast spectroscopy systems.

REFERENCES

1. S. Geiger, “Tailoring the performance of q-switched, solid state lasers – why

and how,” Solid State Lasers XV: Technology and Devices, Proc. SPIE, Vol.

6100, pp. 458–466 (2006).

2. A. Galvanauskas, M.C. Swan, C.H. Liu, “Effectively-Single-Mode Large

Core Passive and Active Fibers with Chirally-Coupled-Core structures,”

CLEO/QELS Conf. and Photon. Appl. Sys. Technol., OSA Technical Digest

(CD), Optical Society of America, paper CMB1 (2008).

3. M. Li, X. Chen, A. Liu, S. Gray, J. Wang, D. Walton, L. Zenteno, “Effective

Area Limit for Large Mode Area Laser Fibers,” OFC/NFOEC, OSA Technical

Digest (CD), Optical Society of America, paper OTuJ2 (2008).

4. C. Liu, S. Huang, C. Zhu, A. Galvanauskas, “High Energy and High Power

Pulsed Chirally-Coupled Core Fiber Laser System,” in Advanced Solid-Sta-

te Photonics, OSA Technical Digest Series (CD), Optical Society of America,

paper MD2 (2009).

5. K.-C. Hou, S. George, A.G. Mordovanakis, K. Takenoshita, J. Nees, B. Lafon-

taine, M. Richardson, and A. Galvanauskas, “High power fi ber laser driver

for effi cient EUV lithography source with tin-doped water droplet targets,”

Opt. Exp. 16, pp. 965–974 (2008).

Phill Amaya is CEO of Arbor Photonics Inc., Ann Arbor, MI 48105; e-

mail [email protected]; www.arborphotonics.com.

Tell us what you think about this article. Send an e-mail to LFWFeedback@

pennwell.com.

Optical-Sectioning continued from page 49

bottom surfaces; the sample itself was tilted slightly with

respect to the image plane due to a tilt in the sample stage.

In addition to optical sections, a “control” image was taken

with the single-pixel detector replaced with a CCD array and

with all the DMD mirrors turned on.

The neighboring sections were 2 μm apart from each other

along the optical axis. When compared to the control image,

the optical sections show more contrast between the rough

and smooth portions of the sample, thus better revealing the

variations in surface texture.

Gonzalo Arce, one of the researchers, notes that for fi ner reso-

lution, higher-NA objective lenses can easily be used in the setup.

“In terms of the next step in the experimental setup, we plan

to extend the current single-path architecture to a dual-path

compressive confocal architecture,” he says. “In a single-path

mode, we use the conjugate image only. The dual-path compres-

sive confocal microscope (CCM) exploits both the conjugate

and the nonconjugate images. The dual-path CCM, in theory,

allows us to simultaneously reach signal-to-noise-ratio values

and acquisition times that are not possible with other existing

confocal microscopy systems. In addition, we are modifying a

scientifi c-grade microscope into a CCM system. This upgrade

will give us more-convenient interfaces to different objective

lenses, better optical-alignment accuracy, lower noise contami-

nation, and a more rigid system construction.”

REFERENCE

1. Y. Wu et al., “A single-pixel optical sectioning programmable-array micro-

scope,” SPIE Photonics West 2010, Conference 7596, Jan. 27, 2010.

Tell us what you think about this article. Send an e-mail to LFWFeedback@

pennwell.com.


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Linear arraydetector

α

Matrix array(CCD)

α


Prism-based spectrometers tackle today’s miniaturization requirementsJEREMY LERNER

It is truly said that form follows func-

tion; however, increased miniaturiza-

tion inevitably collides with practical

realities. Surprisingly, however, tech-

nologies over 300 years old are fi nally

experiencing a rebirth in cutting-edge

applications. Sir Isaac Newton fi rst de-

scribed the use of a prism to display the

colors present in the sun’s light in 1666.

This promising beginning was soon

usurped by the diffraction

grating and by the late 1800s

grating-based spectrometers

became the de facto stan-

dard. But by the year 2000,

grating-spectrometer de-

velopment had more or less

hit a plateau, failing

to satisfy some of the

more demanding and

emerging applications

that often require min-

iature spectrometers or

microspectrometers in

a handheld or portable

format.

The remote-sensing community,

for example, pioneered the use of

hyperspectral imaging to correlate

objects in a heterogeneous field

of view (FOV) with their spectral

characteristics. To satisfy the needs of

this community, imaging spectrometers

were developed that used prisms and

prism-grating combinations (grisms).

This new generation of imaging

spectrometers has since been adapted

to address complex applications

including automated pathology,

biomedical imaging, and nanoparticle

imaging and characterization.1, 2

Imaging versus non-imaging

spectrometers

In the early 1900s it was observed that

all spectrometers took a point and im-

aged it as a line, at each wavelength, on

the detector. The image of a point on

the entrance slit was not only elongat-

ed due to astigmatism but also suffered

from curvature and other aberrations

(see Fig. 1). This not only made it impos-

sible to differentiate between the spectra

presented by two adjacent objects, but

also spread the light over a large area,

Because a prism transmits 90% of light

over an extended wavelength range,

matching it to a CCD detector with

close to 90% quantum effi ciency creates

a nearly ideal system that, with some

tradeoffs, can be miniaturized to meet

portable spectroscopy application needs.

FIGURE 1. A non-

imaging spectrometer

images a point as a

line (left); an imaging

spectrometer images

spatially separated

points as “points”

on the detector

(right). (Courtesy of

LightForm)

MINIATURIZED IMAGING SPECTROMETERS


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MINIATURIZED IMAGING SPECTROMETERS cont inued

reducing photon density and sensitivity.

A true imaging spectrometer images a

point in the FOV as a point on a detector

at each wavelength. With this capability

it is possible to reconstruct the spectral

characteristics of a heterogeneous FOV,

which satisfi es the imaging requirements

of most applications.

Grating-based imaging spectrometers

reduce astigmatism and other aberra-

tions by using aspheric optics or gratings

with asymmetrically distributed grooves

(ADG) produced holographically, or

with sophisticated ruling engines.3-6

The challenge is to produce a diffraction

grating that possesses the optimum focal

length, groove density, and wavelength

effi ciency, in a size that makes sense.

The quest for lighter, robust, more sen-

sitive spectrometers that operate over

extended wavelength ranges within the

remote Earth-sensing community has

resulted in the development of a new genera-

tion of prism-based, compact spectrometers.

Spectrometer basics

Whether a spectrometer uses a grating or

a prism, all wavelength-dispersive spec-

trometers image an entrance slit onto a

detector, at each wavelength. Unlike a

classical spectrometer, an imaging spec-

trometer dissects the image of the en-

trance slit along its length (perpendicu-

lar to the wavelength dispersion axis). In

use, an FOV is imaged onto the slit; then,

all objects appearing along the slit pres-

ent their spectra to the detector. To gener-

ate a spectral map, referred to as a hyper-

spectral image, the spectrometer is either

fl own over the FOV or the FOV is translat-

ed underneath the spectrometer on a con-

veyor belt or automated translation stage.

In both cases the spectrometer is used as

a spectrograph in which all wavelengths

are acquired simultaneously at each lo-

cation along the slit.

The ideal wavelength detector for an

imaging spectrometer is a CCD camera

where each row of pixels is assigned to

a location on the entrance slit. Each row

of pixels acquires a complete spectrum

from each location and the spectrum of

each point on the slit is dispersed across

a specifi c row of pixels. The spatial res-

olution is limited by the height of a row

of pixels and the spectral resolution

is determined by the properties of the

spectrometer, unless the CCD camera

is mismatched to the spectrometer. After

establishing the required spatial/spectral

resolution and wavelength range of the

application, the operating parameters

of the instrument can be calculated.7, 8

Spectral and spatial resolution

Given that the entrance slit is imaged

onto the detector bandpass, spectral

resolution (or bandpass BP) is defi ned

as BP = Sw

* Wd. Here, S

w = image of

the entrance slit (mm) and Wd = wave-

length dispersion (nm/mm). The aver-

age wavelength dispersion, Wd, is the re-

quired wavelength range divided by the

length of a row of pixels. If the appli-

cation characterizes a fi eld of nanopar-

ticles then the wavelength range needs

to stretch from 400 to 800 nm—a 400

nm spectral segment. And if each pixel

in the CCD detector is 4.65 × 4.65 μm

arrayed along rows 6.47 mm in length,

then the average Wd will be 400 divided

by 6.47 mm, or 62 nm/mm.

Assuming the application demands a

spectral resolution of better than 2 nm

(and for expediency it would be desir-

able to use is a standard 25 μm slit width),

then the system bandpass will be 0.025 ×

62, or 1.55 nm. Actual values of Wd and

Sw

vary with wavelength, so spectral reso-

lution will vary across the spectral range.

The image of the entrance slit will

present a full width at half maximum

(FWHM) of approximately 25 μm (Sw)

and will occupy an integer number of

pixels, with the number of pixels defi n-

ing the FWHM as 25/4.65 or 6.

Only three pixels are required to accu-

rately determine the peak wavelength

and the half maximum points; therefore,

there would be no loss in spectral reso-

lution and a gain in sensitivity if rows

of pixels were binned two by two. This

condition satisfi es the Raleigh criterion

for spectral resolution when the FWHM


M SaGEF


M SaGEF

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CCD

Prism withcurved sides

Objects in a field of view


is that of the entrance slit when illumi-

nated by a monochromatic wavelength

such as a single-mode laser or a low-

pressure mercury discharge lamp. It is

worth emphasizing that spectral resolu-

tion depends on the width of the image

of the entrance slit, not the total number

of pixels on the CCD chip.

A spectrometer’s spatial resolution is

determined by the convolution of resid-

ual spectrometer aberration and the

height of a row of pixels. The net spa-

tial resolution is a quadratic where spa-

tial resolution equals the root of the sum

of the squares of residual system aberra-

tions, the size of a pixel, and any other

contributing factors.

A minimum of at least two pixels are

required to determine the location of an

object on the entrance slit; therefore, if the

FOV is imaged with a 40X microscope

objective the spatial resolution at the FOV

would be approximately 0.45 μm.

Correcting aberrations in a

prism-based spectrometer

Diffraction-grating spectrometers enable

aberration correction through modifi ed

groove distribution or the use of aspheric

focusing or collimating optics. The use

of aspheric optics with a prism is feasi-

ble, but unnecessary

if the prism itself can

be given “power” (see

Fig. 2). This special

power geometry used

optics with curved

sides, and was orig-

inally developed for

the SEBASS remote

hyperspectral imag-

ing system (www.lpi.

usra.edu/science/kirk

land/home.html) that

is fl own on aircraft

and operated in the far-infrared spec-

trum. A redesign for use in the wave-

length range from 365 to 920 nm resulted

in LightForm’s PARISS hyperspectral im-

aging system (www.pariss-hyperspectral-

imaging.com) for use mounted on any

microscope for biomedical, forensic, and

industrial spectral imaging.9

The optical system comprises a prism

with one side concave, the other con-

vex, and a spherical mirror for focus-

ing. The effective wavelength dispersion

is doubled because light passes through

the prism twice. Ray tracing is used to

determine the optimum curves of the

mirror and prism faces and the distances

between the mirror and prism.

Grating- versus prism-based

spectrometers

Diffraction-grating effi ciency varies con-

siderably with wavelength and peaks at the

blaze wavelength (see Fig. 3). If a grating

is non-blazed, such as many holographic

gratings, the peak effi ciency is lower but

can extend over a longer wavelength range.

In comparison a prism has a fl at 90%

transmission effi ciency over a very wide

wavelength range. This makes it feasi-

ble to use signifi cantly less expensive

cameras with lower quantum effi ciency

(QE). The majority of wavelength-sensi-

tive detectors (including photomultiplier

tubes, CCDs, and most silicon-based

detectors) have QE profi les that are very

similar to the effi ciency profi les of blazed

diffraction gratings.

For both a prism and a typical

diffraction grating, wavelength

dispersion is nonlinear. But because

the nonlinearity is greatest for a prism,

there is a surprising benefi t: Given that

spectral resolution and bandpass are

a function of wavelength dispersion,

a decrease in wavelength dispersion

FIGURE 2. An aberration-correcting prism spectrometer uses

optics with curved rather than fl at sides, somewhat like a lens

with a severe wedge. (Courtesy of LightForm)


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to longer wavelengths

results in a decrease

in spectral resolution.

Therefore, the spectral

resolution of prism

spectrometers is greatest

in the blue and lowest in

the red. However, light

throughput is directly

proportional to bandpass.

This is an advantage when

working with weakly

emitting samples because

as the QE of the camera

decreases, the light

throughput of a prism

increases as a function of

its bandpass (see Fig. 4).

Optimizing the size and

weight of any spectrome-

ters can be a juggling act

depending on the applica-

tion. When imaging spec-

trometers are used with a

telescope or microscope

to image an FOV onto

the entrance slit, it can be

a challenge to get enough

light through the system

with a slit width much

less than 25 μm. This

challenge, as well as the size of the CCD

chip and any linear dispersion in the sys-

tem, combines to defi ne the focal length

and groove density of the grating if this

is to be the wavelength-dispersive ele-

ment. The same is true for a prism sys-

tem except that only the focal length is

really negotiable.

Our PARISS prism-based imaging

spectrometer covers the entire spectral

range from 365–920 nm, is about 200

mm in length, and weighs approximately

2 kg—much of which is due to the

scientifi c CCD camera. A comparable

grating system is likely to be about

the same size and weigh up to 3 kg.

The high optical effi ciency, imaging

integrity, and immunity from diffraction

effects makes prism-based imaging

spectrometers a compelling addition to

the spectroscopist’s tool box.

REFERENCES

1. D.T. Dicker et al., Cancer Biology and Therapy 8,

1033–1038 (2006).

2. J. Aaron et al., Nano Letters 9, 10, 3612–3618 (2009).

3. M.P. Chrisp, “Aberration-Corrected Hologra-

phic gratings and their mountings,” in Applied

Optics and Optical Engineering, R.R. Shannon

and W.C. Wyant, Editors, Academic Press, Lon-

don, 391–451 (1987).

4. E. Loewen and E. Popov, Diffraction Gratings

and Applications, Marcel Dekker, New York,

NY (1997).

5. J. Reader, J. Opt. Soc. Am. 59, 1189–1196 (1969).

6. X. Prieto-Blanco et al., Opt. Exp. 14, 20, 9156–

9168 (2006).

7. J.M. Lerner, Cytometry 69A, 8, 712–734 (2006).

8. J. James and R. Sternberg, The Design of Optical

Spectrometers, Chapman & Hall, London (1969).

9. D. Warren et al., “Compact prism spectrographs

based on aplanatic principles,” Opt. Eng. 36,

1174–1182 (1997).

Jeremy Lerner is president of LightForm Inc.,

825C Merrimon Ave., Suite 351, Asheville, NC

28804; e-mail: [email protected]; www.

lightforminc.com.

MINIATURIZED IMAGING SPECTROMETERS cont inued

FIGURE 3. The effi ciency profi les are shown for blazed gratings,

non-blazed (holographic) gratings, and a prism, as well as

camera quantum effi ciency (QE). (Courtesy of LightForm)

FIGURE 4. The wavelength dispersion profi les of prism and

diffraction gratings are compared. Bandpass decreases with

wavelength dispersion. In the case of a prism the decrease

in bandpass compensates for the fall in QE of the camera,

resulting in an increase in sensitivity. (Courtesy of LightForm)


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JEFF HECHT, contributing editor

Shifting semiconductor laser wavelengths poses challenges

Nonlinear optics offer invaluable ways

to fi ll gaps in the laser spectrum, from

simple harmonic generation to more

complex optical parametric oscillators

(OPOs). Frequency doubling of diode-

pumped neodymium

(Nd) lasers has made

green laser pointers

cheap and compact,

but why can’t devel-

opers drop the diode

pumping and directly

double semiconductor laser output to

produce hard-to-fi nd wavelengths?

It’s been done for green light and

is already reaching the market in

pico-projectors from companies like

MicroVision (Redmond, WA).

But it’s not easy. Nonlinear wave-

length conversion requires not

only raw power but also high

beam quality and narrow-line

emission. It’s tough to combine all

those features in a semiconductor

laser. Yet progress is being made.

The fi rst products are on the mar-

ket, and developers are reporting

more encouraging results, includ-

ing new laser designs, diode pump-

ing of OPOs, and both harmonic

generation and difference-fre-

quency generation

with quantum cas-

cade lasers.

Quests for

doubled diodes

Serious work on di-

rect doubling of di-

odes started in the

early 1990s, when

diodes had reached high pow-

ers and the diode laser spectrum

stopped in the red. Doubling the

output of near-infrared diodes prom-

ised inexpensive sources for the short

end of the visible spectrum. It also

offered directly modulatable short-

wavelength lasers for applications

such as laser displays.

Coherent Inc. (Santa Clara, CA)

succeeded in developing a product

called the D3 (for direct-doubled-

diode) laser, which frequency dou-

bled the roughly 100 mW of an 860

nm diode to produce about 10 mW of

blue light at 430 nm.1 It required a dis-

tributed Bragg refl ector laser for nar-

row-line output, and the diode output

had to be mode-matched and phasel-

ocked into the external harmonic gen-

erator. It was a fi rst, but it found few

applications and eventually faded

away—no doubt partly because of

Shuji Nakamura’s remarkable success

in developing blue indium-gallium

nitride diode (InGaN) lasers at the

Nichia Chemical Corp. (Tokushima,

Japan). Coherent eventually devel-

oped optically pumped surface-emit-

ting semiconductor lasers, which are

frequency doubled to emit at visible

wavelengths but behave more like

solid-state lasers than diodes.

The success of blue diode lasers left

a gap in the green center of the vis-

ible spectrum, which emerged as a

problem a few years later as the con-

sumer electronics industry looked

for new technology for projection

television. Laser back-projection

promised a better color gamut than

fl at-panel displays, if a suitable laser

Nonlinear optics can generate new lines

from semiconductor lasers by harmonic

generation and frequency mixing, but

it requires high power, good beam

quality, and narrow linewidth.

FIGURE 1. Corning’s

green laser module for a

pico-projector is 4 mm

thick and shown sitting

on a smart phone for

scale. (Courtesy of

Corning Inc.)

P H O T O N I C F R O N T I E R S : FREQUENCY-SHIFTED DIODE LASERS


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FREQUENCY-SHIFTED DIODE LASERS cont inued

source were available at about 530 nm.

Doubled Nd might have seemed a logi-

cal choice, but it couldn’t be directly

modulated at the required speed, so

developers turned to doubling 1060

nm diodes or other lasers to produce

530 nm green beams. Many of those

projects wound down as rear-projec-

tion television faded from the consumer

market, but a few shifted toward com-

pact pico-projectors for mobile devices,

where cost points are lower than for

televisions, says John Nightingale, an

optical consultant in Portola Valley, CA.

Corning Inc. (Corning, NY) is already

carving a niche out of the young pico-

projector market. Last year it intro-

duced a commercial version and is

supplying lasers to MicroVision for its

Showwx projector for iPods and laptops.

Corning’s green laser doubles the 1060

nm output of a distributed Bragg refl ec-

tor (DBR) laser emitting a single-spatial

mode and single frequency. The laser

includes three sections: one a DBR grat-

ing, a second for phase adjustment, and a

third for gain. Corning initially reported

generating up to 104.6 mW at the 530

nm second harmonic by coupling the

infrared DBR output into a periodically

poled lithium-niobate second-harmonic

generator.2 Measurements showed that

the green light could be modulated at

rates above 50 MHz as required for pro-

jectors, and later laboratory versions

reached green output of 184 mW.3

Corning’s fi rst commercial model,

introduced last year, emits 60 mW (see

Fig. 1). In May 2010 the company intro-

duced a prototype 80 mW version that

it says has wall-plug effi ciency of 8%

and can be modulated at speeds to 150

MHz as needed for extended graphics

resolution.

Tapered amplifi er lasers

Another approach to generating the

high-quality, high-power beam need-

ed for effi cient harmonic generation is

FIGURE 2. The tapered amplifi er developed at the Braun Institute includes a 2 mm length

of 4 μm ridge waveguide, with a 1 mm DBR at the back and a 1 mm gain section. The

remaining 4 mm amplifi er stage is tapered at 6°.4

One approach to generating

the high-quality, high-

power beam needed

for effi cient harmonic

generation is combining

a single-mode ridge

waveguide DBR laser with

a tapered amplifi er stage.


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FREQUENCY-SHIFTED DIODE LASERS cont inued

combining a single-mode

ridge waveguide DBR diode

laser with a tapered ampli-

fi er stage (see Fig. 2). Götz

Erbert’s group at the Fer-

dinand Braun Institute for

High-Frequency Technolo-

gy (Berlin, Germany) is in

the midst of a fi ve-year proj-

ect to develop compact sec-

ond harmonic sources with

output to a few watts in the

visible for a range of appli-

cations, from cinema-scale

projectors to precision spec-

troscopy. The group has

generated fundamental out-

put at 980 nm with 0.012

nm linewidth, power to 12

W, and a nearly diffraction

limited beam with vertical

divergence less than 15°.4

Single-pass second-harmon-

ic generation in periodically

poled lithium niobate gener-

ated more than 1 W at 488

nm. The group also is explor-

ing nonlinear techniques for

generating light from the ul-

traviolet to the infrared, and

together with Sina Riecke of

PicoQuant GmbH (Berlin,

Germany) has produced 30

ps pulses at 531 nm and megahertz rep-

etition rates.5

The Braun Institute group also is

working with the University of Potsdam

on a coupled ring resonator for harmonic

generation (see Fig. 3). The main ring

optically locks a tapered amplifi er laser

with the ring resonance, and couples the

fundamental output into a smaller ring

that contains a periodically poled lith-

ium niobate harmonic generator. Recent

experiments generated 310 mW of 488

nm output with 50 MHz linewidth at

18% optical conversion effi ciency.6

A joint project with Paul Michael

Petersen’s group at the Technical

University of Denmark (Roskilde,

Denmark) yielded fundamental output

of 1.38 W from a tunable diode between

659 and 675 nm with linewidth of 0.07

nm.7 The output is the highest from a

tunable diode in this range, and could

be doubled to the 335 nm range, shorter

than current ultraviolet diode lasers.

Combining the high-quality near-

infrared lasers with nonlinear optics also

can generate longer infrared wavelengths

where good sources are not available,

says Erbert. Together with the University

of Twente (Enschede, the Netherlands)

his group used 8.05 W at 1062 nm from

a monolithic diode amplifi er to pump a

singly resonant optical parametric oscil-

lator of periodically poled lithium nio-

bate. Tuning ranges were 1541 to 1600

nm for the signal wave and 3154 to 3415

nm for the idler. The idler power exceed-

ing 1.1 W at 3373 nm, the highest yet

FIGURE 3. Coupled ring resonators for diode-laser

harmonic generation developed by Potsdam-Braun

Institute Team feature a tapered amplifi er laser (TA) in the

top ring, along with a holographic diffraction grating (G),

an optical diode, a half-wave plate (HWP), a polarizing

beamsplitter (PBS), a beamsplitter (BS), and several

lenses. A periodically poled lithium niobate harmonic

generator (PPLN) is shared by the upper and lower ring.6


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from a diode-pumped OPO, and its

44% optical-to-optical conversion effi -

ciency made overall electrical to opti-

cal effi ciency 14.9%, about seven times

higher than from pumping an OPO with

a diode-pumped laser.8

Shifting quantum cascade

laser wavelengths

Nonlinear wavelength shifting is also

a hot topic for quantum cascade lasers,

where the major goals are second-har-

monic conversion, and difference-fre-

quency mixing to generate terahertz

frequencies.

The main interest in second harmonic

generation is to reach C-H, O-H, and

N-H stretching bands of hydrocar-

bons near 2.5–3.5 μm, which would

open important new applications, says

theorist Alexey Belyanin of Texas

A&M University (College Station, TX).

Problems with heterostructure growth

and current injection have hampered

development of quantum cascade lasers

with direct output at such short wave-

lengths. The fi rst observations of har-

monic generation in quantum cascade

lasers were made several years ago by

a collaboration involving Belyanin and

Frederico Capasso and Claire Gmachl,

then both at Bell Labs (Murray Hill,

NJ), but the power was limited to tens

of nanowatts.9 By 2004, they had raised

second harmonic power to milliwatt lev-

els at 4.45 μm.10 The harmonic genera-

tion occurs within the quantum cascade

structure itself. “Since we basically do

‘quantum engineering’ of the optical

nonlinearity, we can control it at our

will,” says Belyanin. That increases non-

linearity far above that of other materi-

als, and aids phase matching by shifting

electron resonances.11 He recently pro-

posed a way to generate second har-

monics as short as 1.5–2.5 μm and is

working with experimentalists to dem-

onstrate the idea.12

The appeal of difference-frequency

mixing for generating terahertz radiation is

the ability to operate at room temperature,

which for most applications is preferable

to the cryogenic cooling required for direct

terahertz emission from quantum cascade

lasers. The tradeoff, says Belyanin, is that

“there’s no free lunch because you lose a

lot of power.”

Difference-frequency generation

requires producing a quantum cascade

laser that operates at two separate wave-

lengths, which mix in the laser cavity

to generate the difference frequency.

“The terahertz output is modest, but it

is there,” says Mikhail Belkin of the

University of Texas at Austin (Austin,

TX), who mixed 7.6 and 8.7 μm wave-

lengths to generate the 60 μm difference

frequency while working with Capasso

at Harvard.13 “Theoretically we could

get milliwatts, but experimentally we

only get about 1 μW at room temper-

ature,” adds Belkin, who is continuing

this work in Austin. The good news is

that he sees plenty of opportunities to

raise the power further. Cryogenically

cooled terahertz quantum cascade lasers

can emit up to 150 mW but only at very

low temperatures, declining at higher

temperatures and to zero above 190 K.

Competition and outlook

Recent progress on green diode lasers

shows clear competition. At Photon-

ics West, Nakamura, now at the Uni-

versity of California at Santa Barbara

and Kaai (Santa Barbara, CA), an-

nounced a 523 nm green diode, and

Osram Opto Semiconductors (Regens-

berg, Germany) reported 50 mW out-

put in the laboratory from a 515 nm

InGaN laser.14 Yet Osram isn’t giving

up on doubling optically pumped sur-

face-emitting semiconductor lasers to

produce green light, and Corning is de-

livering products that are being built

into pico-projectors. Green diodes will

have to catch up in power and reliabil-

ity, and for all their appeal, there is no

guarantee they can beat doubled di-

odes—especially at the watt level. Oth-

er nonlinear wavelength shifting is on

the cutting edge of progress. Results

are encouraging, but we will have to

wait for the fi nal results.

REFERENCES

1. http://www.repairfaq.org/sam/laserdio.

htm#diocod

2. M.H. Hu et al., “High-power distributed

bragg refl ector lasers for green-light

generation,” Proc. SPIE 6116, 61160M,

doi:10.1117/12.647840 (2006).

3. J. Gollier et al., “P-233: Multimode DBR La-

ser Operation for Frequency Doubled Green

Lasers in Projection Displays,” Corning In-

corporated, Science and Technology, Cor-

ning, NY 14831, USA; available at http://

www.corning.com/WorkArea/downloadasset.

aspx?id=10533.

4. C. Feibig et al., “High-power DBR tapered

laser at 980 nm for single-path second-

harmonic generation,” IEEE J. Selected Topics

in Quant. Electron. 15, 978–983 (May–June

2009).

5. S.M. Riecke et al., “Pulse shape improvement

during amplifi cation and second-harmonic

generation of picosecond pulses at 531 nm,”

Opt. Lett. 35, 1500–1502 (May 15, 2010).

6. D. Skoczowsky et al., “Effi cient second-harmo-

nic generation using a semiconductor tapered

amplifi er in a coupled ring-resonator geometry,”

Opt. Lett. 35, 232–234 (Jan. 15, 2010).

7. M. Chi et al., “1.38 W tunable high-power

narrow-line external cavity tapered amplifi er

at 670 nm,” CLEO/QELS 2010, paper JTuD99.

8. A.F. Nieuwenhuis et al., “One-watt level mid-

IR output, singly resonant continuous-wa-

ve optical parametric oscillator pumped by a

monolithic diode laser,” Opt. Exp. 18, 11123

(May 24, 2010).

9. N. Owschimikow et al., “Resonant second-

order nonlinear optical processes in quantum

cascade lasers,” Phys. Rev. Lett. 90, 043902

(Jan. 31, 2003).

10. O. Malis et al., “Milliwatt second harmonic

generation in quantum cascade lasers with

modal phase matching,” Electron. Lett. 40

(Dec. 9, 2004).

11. M. Belkin et al., “Quasiphase matching of

second-harmonic generation in quantum

cascade lasers by Stark shift of electronic

resonances,” Appl. Phys. Lett. 88, 201108

(2006).

12. Y.-H. Cho and A. Belyanin, “Short-wavelength

infrared second harmonic generation in qu-

antum cascade lasers,” J. Appl. Phys. 107,

053116 (2010).

13. M. Belkin et al., “Terahertz quantum-cascade

laser source based on intracavity differen-

ce-frequency generation,” Nature Photon. 1,

288–292 (May 2007).

14. S. Lutgen, A. Avramescu, T. Lermer, M.

Schillgalies, D. Queren, J. Müller, D. Dini, A.

Breidenassel, U. Strauss, “Progress of blue

and green InGaN laser diodes,” invited talk at

Photonics West 2010, to be published in Proc.

SPIE 7616.

Tell us what you think about this article. Send an

e-mail to [email protected].


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material. They can also be used for

annealing, crystallization, and temper-

ing of thin fi lms with high-speed linear

scanning processes and for rapid ther-

mal inspection and quality assurance.

LIMO

Dortmund, Germany

www.limo.de

Dual-CCD camera

The new ORCA-D2 is a dual-CCD

camera is designed around two ER-150

CCD devices. It can capture simulta-

neous dual-wavelength or multiple

focal-plane images. Each CCD captures

a 1280 × 960 pixel fi eld of view and

has independent exposure and gain

settings to accommodate signifi cantly

different intensity levels between the

two images as is often seen in FRET and

ratio imaging applications.

Hamamatsu

Bridgewater, NJ

[email protected]

Optical transceiver modules

SFP+ optical transceiver modules for

next-generation 10 Gbps Ethernet

equipment designs include the 10/1

Gbps dual-rate AFCT-701SDDZ

10GBase-Long Range (LR) single-mode

and AFBR-703SDDZ 10GBase-Short

New products


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New products


Range (SR) multimode fi ber transceivers.

Designed for use in enterprise and data

center applications, the dual-rate opera-

tion allows fl exibility in data rate control

through hardware or software control.

Avago Technologies

San Jose, CA

[email protected]

CCD cameras

The Clara CCD camera, based on mea-

sured QC data from the fi rst 200 cam-

eras built, has reduced typical read noise

to 2.4 electrons at 1 MHz. Cooling is

now offered to -55ºC with an internal

fan only (no water required), with -20ºC

under fan-off (vibration-free) opera-

tion. Features include a 1.3 Mpixel Sony

‘ICX285 sensor, low-noise 10 or 20 MHz

readout modes, and data channeled

through a USB 2.0 interface.

Andor

Belfast, Northern Ireland

www.andor.com/clara

Image analysis software

ImageUV microscope camera con-

trol and image analysis software is

designed for Windows 7. It features

quick resizing of windows, more visible

icons, and quick access to often used

documents and spectra with Jump

Lists. Windows Search gives engineers

and scientists a search engine to locate

and analyze data with the company’s

UV-visible-NIR microscopes.

CRAIC Technologies

San Dimas, CA

[email protected]

Strain sensors

The DT series of strain sensors allow

undercarriage structures and surfaces

to be more accurately monitored com-

pared to counting accelerometer meth-

ods. These rugged sensors incorporate

the technology of the fl ight-qualifi ed

DTD2684. Series DT3625 Sensors offer

a package of 0.45 × 0.25 × 0.14 in.

thick and weigh only 13 grams. They

are designed to monitor the fatigue

loading experienced by aircraft under

various conditions of fl ight speed,

weight, and mission confi guration.

Columbia Research Laboratories

Woodlyn, PA

[email protected]

Optical fi ber test platform

The Fiber Lab 800HE testing plat-

form targets applications where rough

handling and harsh conditions are

common, such as fi eld and laboratory

testing, manufacturing environments,

and military systems. The company is

also making the platform available for

customization with preconfi gured fl aws

in the fi ber to support CATV and tele-

com test equipment training.

M2 Optics

Holly Springs, NC

www.M2optics.com

Color smart camera

The BOA vision system, a highly inte-

grated smart camera, now has color

processing, which covers a broad range

of color inspection applications in the

automotive, food, packaging and phar-

maceutical industries, such as identi-

fi cation of parts or assembly features,

sorting, counting, and verifi cation of

color hue. Features include the iNSpect

Express software interface, 44 mm3

form factor, and IP67-rated housing.

DALSA

Waterloo, ON, Canada

www.dalsa.com

Prismatic multispecies

gas analyzer

The Prismatic Multi-Species Gas Analyzer

is a single analyzer that can measure

trace levels of as many as 16 different

molecules using continuous-wave cavity


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StarLab 2.00 software

1-866-755-5499

www.ophir-spiricon.com

Turn your PC into a laser power &

energy measurement work station

� 8 channels

� Math functions

� Data Logging

Made for Accuracy

Designed to measure

The True Measure of Laser PerformanceTM

The first concept of a programmable computer

was originated by Charles Babbage in England

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New products

ring-down spectroscopy (CW-CRDS).

It relies on a patented technique that

utilizes Brewster’s angle retrorefl ector

prisms to gain high refl ectivity over a

wide wavelength range.

Tiger Optics

Warrington, PA

www.tigeroptics.com

Bandpass fi lters

Bandpass interference fi lters are used

to selectively transmit a narrow range

of wavelengths while blocking others.

They are available as “traditional” coated

fi lters and high-performance “hard”

coated fi lters, which are fabricated via

an advanced plasma reactive sputter-

ing platform. Custom hard coated fi lters,

with optical densities greater than 6.0,

transmission greater than 90%, and edge

steepness less than 0.5%, can be rapidly

developed for OEM instrumentation.

Edmund Optics

Barrington, NJ

[email protected]

Optical components

for CV sensor system

Polymer optical components manu-

factured for the Closing Velocity (CV)

sensor system are known as “City

Safety.” The transmitter and receiver

unit of the system calculates the dis-

tance to objects and its approach speed

from signals in the range up to 10 m.

Jenoptik Business Unit

Triptis, Germany

www.jenoptik-los.com

High CRI, 0.5 W LED

The NWA-BSC is a high Color Rendering

Index (CRI) product in a 0.5 W white

version. Compliant to US Energy Star

guidelines, it fulfi lls the required mini-

mum CRI of 75. The LED has an oper-

ating current of 150 mA and achieves

typical 20 lm at a low thermal resistance.

The package dimensions are 3.5 × 3.5 ×

1.2 mm with a viewing angle of 120°.

Dominant Semiconductors

Melaka, Malaysia

www.dominant-semi.com

Collimating lenses

New aspheric molded lenses are designed

for collimating light from MWIR and

LWIR lasers, such as quantum cascade

lasers (QCLs). Manufactured from Black

Diamond chalcogenide glass, lenses have

a high NA for maximum light collection.

Antirefl ective coatings are available for the

SWIR (1.8–3 mm), MWIR (3–5 mm), and

the LWIR (7–12 mm) wavelength ranges.

Lightpath Technologies

Orlando, FL

www.lightpath.com

Nanopositioning stages

The new nano1x3 series x-y and x-y-z

nanopositioning stages are designed for

inverted microscopes from Leica, Nikon,

Olympus, and Zeiss. The low-profi le

design of 20 mm (0.8 in.) facilitates inte-

gration while a large aperture accom-

modates microscopy accessories such

as slide holders and Petri dish holders.

Other features include 200 μm x-y or

x-y-z travel and a 24 bit controller.

Physik Instrumente (PI)

Auburn, MA

[email protected]

Warm white LED

A warm white LED prototype is designed

for general illumination applications. It

provides a color temperature of 3000 K

and a color rendering index of 82. With

operating current of 350 mA and chip

surface of 1 mm2, the prototype of the

new single-chip LED achieves a bright-

ness of 124 lm, which corresponds to an

effi ciency of 104 lm/W.

Osram Opto Semiconductors

Sunnyvale, CA

[email protected]


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Manufacturers’ Product Showcase


IR Wavelength meters for Pulsed &

CW lasers covering from the UV to Mid-IR

When only the

most accurate

results matter,

TOPTICA delivers!

Our wavelength

meters are the

most accurate

with the best

resolution specs

commercially available. With the only high resolution

wavelength meter capable of reaching 2MHz!

All of our wavelength meters incorporate standard features:

• Models from 192-2250nm for broad coverage options

• Measurement speeds to 600Hz for the fastest results

• No moving parts ensuring greater stability

• Integrated calibration minimizing downtime

• PID control to drive your lasers

• Linewidth measurement offering greater capability

www.toptica.com

(585) 657-6663 • [email protected]

Conex™-MFACC Integrated

Linear Stage and Controller

This latest Newport innovation combines the popular MFACC

stainless steel linear stage with an inexpensive and compact

motion controller. This integrated confi guration allows easy

USB connection and simplifi es remote control of repetitive

tasks in optical setups. Conex, the superior performance of

Newport motion products, at affordable prices.

Newport Corporation

www.newport.com • (800) 222-6440

6100 Combo Laser Diode

and Temperature Controller

Newport’s new Model 6100 Combo Laser Diode and

Temperature Controller is equipped with an impressive

software suite that will allow you to make serious

measurements in a matter of minutes. The suite consists of

a high speed LIV characterization and a temperature tuning

software for TEC with a full PID parameter control. For the

LIV characterization, also consider using Newport’s optical

power meters such as the 1936-C.

(Newport logo)

Newport Corporation

www.newport.com • (800) 222-6440

A New Way to Accurately Measure Color

TRICOR Systems Model 600 Non-Contact Imaging

Spectrophotometer will allow the user to capture image data

from any scene and provide CIE Chromaticity Coordinates

of each pixel located in that scene. Quantify spectral

transmittance, refl ectance and output from illumination and

or display systems. The Model 600 can be used to measure

radiated sources, refl ectance as well as transmittance from

380nm to 780nm. This spectral information can be used to

calculate various color coordinates of refl ectance colors

under various types of illuminants. Color units include: XYZ,

xyz, L*a*b*, Lab, u’v’, L*u*v* and CCT.

1650 Todd Farm Dr., Elgin, IL 60123 • 847-742-5542

www.tricor-systems.com • [email protected]


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Manufacturers’ Product Showcase

One-year subscription to LASER FOCUS WORLD FREE!

Visit us online at www.lfw-subscribe.com

or call Customer Service at 847.559.7500

New USB Control Interface

FEMTO Messtechnik GmbH just introduced the new USB

Control Interface LUCI-10 for the remote control of FEMTO

amplifi ers and

photoreceivers

directly from a

PC. The interface

supports opto-

isolation of the

PC USB port

from the signal

path of the

connected amplifi er module to guarantee signal integrity

and low noise performance. The LUCI-10 electronics is fully

integrated inside the D-Sub hood and bus-powered through

the USB port. It comes with an extensive software package

containing the necessary DLL driver and software examples

like Graphic User Interfaces (GUI’s), sample VI’s and a

FEMTO Library to help generate your own control software

in a LabVIEW™ environment.

FEMTO Messtechnik GmbH

Paul-Lincke-Ufer 34, 10999 Berlin, Germany

(p) +(49) 30-446 93 86, (f) +(49) 30-446 93 88

e-mail: [email protected], http://www.femto.de

NEW! Fiber Laser Focusing Lenses

from OPTOSIGMA Corp.

• High performance Multi-Element lenses, suitable for

focusing and collimating solid state lasers such as Yb

Fiber laser, YAG laser and YV04 laser

• Optimized AR coating from 1040nm – 1150nm; maintaining

Transmittance at 633nm for HeNe pointing lasers

• Corrected for spherical aberration and coma @1064 nm.

Lens is diffraction limited for f# >2 (NA < 0.25)

• Lens optimized to reduce the effect of thermal expansion

by using all fused silica elements

www.optosigma.com

OPTIMIZED TO REDUCE THERMAL LENSING


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Cargille Laboratories

Cargille Labs, started in 1924,

develops and manufactures

Optical Liquids calibrated

for Refractive Index for use

throughout many laboratory

disciplines involving microscopy

and/or optics, ex: aerospace,

telecommunications, particle

identifi cation, hematology,

geology, testing labs, art

conservation, etc. A Specialty

Optical liquids catalog is available

which includes typical optical & physical properties and

comparative diagrams of glasses and optical liquids.

Cargille’s other catalog includes data sheets on Disposable

Beakers, Heavy Liquids, Immersion Oils, Refractive Index

and Immersion Liquids, Plastic Boxes, Reference Sets,

Sample Storage Systems, Micro Slide and Tissue File

Boxes and Viscosity Tubes.

Cargille Laboratories

55 Commerce Road, Cedar Grove, NJ 07009 USA

Tel.: (973) 239-6633, Fax: (973) 239-6096

E-mail: [email protected], www.Cargille.com

FemtoFiber pro — versatile Erbium

doped ultrafast fi ber laser

TOPTICA’s new FemtoFiber

pro is an ultrafast laser featuring

high peak powers along with

completely hands-off operation

while offering excellent

performance. With a focus

on reliability and robustness,

new technologies have found

their way into the professional

graded product, including the

saturable absorber mirror (SAM)

and the use of only polarization

maintaining (PM) fi bers. The

device ensures self-starting

and stable mode-locking under all laboratory conditions.

The FemtoFiber pro is available with fundamental output

at 1560nm with a pulse width well below 100fs (FemtoFiber

pro IR) and also with second harmonic output at 780nm

(FemtoFiber pro NIR).

www.toptica.com

(585) 657-6663 • [email protected]

New Thermal Laser Power Sensors

For powers up to 400W

these high performance,

heat dissipation sensors

feature an array of pins

for cooling, unlike other

devices which rely on fl at

cooling fi ns that consume

signifi cantly more space.

As a result, they are the

most compact laser power

sensors on the market, half

the size of most devices.

www.ophiropt.com/laser-measurement

(866) 755-5499

Passive Q-Switched 1064 nm DPSS Laser

3 mJ, 1MW peak output

This very compact high-energy laser delivers 3 mJ pulses

with pulse durations of 3 ns. The side-pumped, self-aligning

monolithic design allows for high peak powers in a compact

size while providing stable and maintenance-free operation.

321 South Main Street, Suite 102,

Providence, RI 02903 USA

Tel.: (401) 274-4700, [email protected]


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Business Resource Center

Used Equipment

Laboratory EquipmentUsed and Refurbished

Lasers, microscopes, mounts, motorized

and manual stages, vibration tables,

clean room equipment and more!

‘Like new’ for less than half the cost!

www.photomachining.com/inventory/

[email protected]

603-882-9944

Laser Modules VCSEL / Transceivers

Lasermate Group, Inc. provides high quality and low cost of• 266nm–1625nm lasers including UV, blue, green,

red, & infrared laser diodes, modules & products.• 670nm–850 nm VCSEL chip, array, diode, transmitter

& transceivers• 405nm–1625nm laser diodes including fi ber

coupled pigtail & receptacle packages up to 25W• 1270nm–1610nm DFB lasers for CWDM 18 channels • Analog 1310nm & 1550nm FP & DFB lasers & Analog

InGaAs PIN Photodiode• Up to 10Gbps GaAs & InGaAs PIN photodiodes & arrays• 100M to 10G optical transceivers including 1×9, SFF,

SFP & GBIC with duplex & simplex connectors• 1W to 3W blue, green, red, yellow & white LED

modules• Laser safety goggles and laser accessories• Fiber Optic DVI Extender & HDMI Extender • Fiber Optic Test Tools including fi ber checker, fi ber

meter, fi ber optic light source

Call: (909) 623-4995 Fax: (909) 623-4915E-mail: [email protected]

www.lasermate.com

Optics / Polarizers Manufacturing

INFRARED OPTICSwindows • prisms • lenses • filters

AgBr CdTe KCI Sapphire

AgCl Csl KRS-5 Si

AMTIR GaAs LiF SiO2

BaF2 Ge MgF2 ZnS

CaF2 KBr NaCl ZnSe

CO2 LASER OPTICSlenses • mirrors • beamsplitters

reflectors • output couplers

POLARIZERSwire grid • free-standing • far IR

FIBER OPTICSUV-mid IR single or bundled assemblies

UV SiO2 • GeO • Sapphire • ZrFChalcogenide • Silver Halide

COATINGSanti-reflection • hard carbon

infrared • metalization

REFLEX Analytical Corporation“Serving you across the Spectrum”

PO Box 119 Ridgewood, New Jersey 07451Internet: www.reflexusa.com

E-mail: [email protected]: 201-444-8958 Fax: 201-670-6737

Request our FREE catalog

Used Equipment

ON A BUDGET? NEED EQUIPMENT?

Visit www.lasersurplus.com and discover hundreds of quality new and used items at a fraction of the original cost. All kinds of optical related items are listed with photos and prices.

Don’t hesitate,Have a look today!

Laser Surplus SalesYour optical lab outfitter

(214) 631-LASE (5273)www.lasersurplus.com

WANTEDUsed & Surplus Laser Equipment

FOR SALE

New and used lasers including:

Helium-Neon, Argon, Krypton, Ruby, He-Cd,

Nd:YAG, DPSS, diode laser modules, etc.

Midwest Laser Products, LLCP.O. Box 262, Frankfort, IL 60423

Ph. (815) 462-9500 FAX (815) 462-8955

Web: http://www.midwest-laser.com

email: [email protected]

Optics / Coatings Manufacturing

WAVEPLATES ON DEMANDOptiSource has made a personal commitment

to deliver value to our customers.

Value equals price plus convenience plus reliability.

We maintain a coated inventory of standard waveplate diameters, wavelengths and

retardations. WINDOWS, MIRRORS and LENSES are also available. Please call or email for our

NEW CATALOG or view the catalog and pricing matrix at www.optisourcellc.com

Prompt Response & ServiceCompare Delivery Quality and Pricing

Ph: 505.792.0277 / Fax: 505.792.0281www.optisourcellc.com / [email protected]

102 Mountain Park Pl. NW, Ste. #DAlbuquerque, New Mexico 87114, USA

Optics / Coatings Manufacturing

1324 E. Valencia Dr. Fullerton, CA 92831

www.latticeoptics.com

T: 714-449-0532, F: 714-449-0531

[email protected]

Need optics & coatings?

Quality, quick service & any quantity24 hrs turnaround on most optics & coatings

CUSTOM optics with a lightening quick delivery

One of the largest INVENTORIES in the industry

Then, challenge us!

High power ultrafast laser optics.

High damage threshold optics & coatings.

High damage PBS, high energy beam expanders.

Excimer, YAG, CO2 optics. OPO, crystal & laser rod

coatings, prisms mirrors, windows, beamsplitters,

polarizing optics, waveplates, filters spherical,

cylindrical & aspheric lenses, Etalons

(0.1mm-20mm thk).

Coating service (1 day)

AR, DAR, TAR, BBAR, PR, HR, Hybrid, Metallic

UV(from 157nm), VIS, NIR, Mid IR, Far IR

Catalog

Request our free catalog

Lattice Electro

Optics, Inc.

Put your products where your customers are looking to buy. Sign up today for

“Focus On Products”Contact Katrina Frazer at 603-891-9231

or [email protected]


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ADVERTISING SALES OFFICES

Advertiser&web index


MAIN OFFICE

98 Spit Brook Road, LL-1, Nashua, NH 03062-5737(603) 891-0123; fax (603) 891-0574

Senior Vice President & Group Publisher

Christine A. Shaw (603) 891-9178 [email protected]

Executive Assistant & Reprint Sales

Sharon A. MacLeod(603) 891-9224; [email protected]

Digital Media Sales Operations Manager

Tom Markley(603) 891-9307; [email protected]

Ad Services Manager Steve Archer(918) 831-9473; fax (918) [email protected]

Director, List Sales Bob Dromgoole(603) 891-9128; fax (603) [email protected]

NORTH AMERICA

New England, Eastern Canada & New Jersey

Diane Donnelly, (508) 668-1767: fax (508) 668-4767 [email protected]

Midwest, MidAtlantic, Southeast

Jeff Nichols, (413) 442-2526; fax (413) 442-2527 [email protected]

West and Western Canada

Paul Dudas, (949) 489-8015; fax (949) [email protected]

Inside Sales—Business Resource Center/Classifi ed,

Focus on Products, Product Showcase

Katrina Frazer, (603) 891-9231: fax (603) 891-0574 [email protected]

INTERNATIONAL

UK and Scandinavia Tony Hill44-1442-239547; fax [email protected]

France, Netherlands, Belgium, Spain, Greece,

Portugal, Southern Switzerland

Luis Matutano (Paris) 33-1 3076-5543; fax 33-1 [email protected]

Germany, Austria, Northern Switzerland, Eastern

Europe, Russian Federation

Holger Gerisch49-8801-302430; fax [email protected]

Hong Kong/China Adonis Mak852-2-838-6298; fax 852-2-838-2766 [email protected]

India Rajan Sharma91-11-686-1113; fax [email protected]

Israel (Tel Aviv) Dan Aronovic972-9-899-5813; [email protected]

Japan Manami Konishi81-3-5645-1271; fax [email protected]

Taiwan Cindy Yang886-2-2396-5128 #[email protected]

For all other international sales, please contact:Christine Shaw, Senior VP & Group Publisher (see contact info. above)

This ad index is published as a service. The publisher does not assume any liability for errors or omissions.

Send all orders & ad materials to: Ad Services Specialist, Laser Focus World, 1421 S. Sheridan, Tulsa OK 74112

Laser Focus World Copyright 2010 (ISSN 1043-8092) is published 12 times per year, monthly, by PennWell, 1421 S. Sheridan, Tulsa OK 74112. All rights reserved. Periodicals postage paid at Tulsa, OK 74101 and additional mailing offi ces. Subscription rate in the USA: 1 yr. $150, 2 yr. $275, 3 yr. $375; Canada: 1 yr. $200, 2 yr. $325, 3 yr. $425; International Air: 1 yr. $250, 2 yr. $375, 3 yr. $475. Single copy price: $15 in the USA, $20 in Canada and $25 via International Air. Single copy rate for March issue which contains a Buyers Guide Supplement: $125.00 USA, $155.00 Canada, $185.00 International Air. Digital edition $55.00 yr. Paid subscriptions are accepted prepaid and only in US currency. SUBSCRIPTION INQUIRIES: phone: (847) 559-7520, fax: (847) 291-4816. (POSTMASTER: Send change of address form to Laser Focus World, POB 3425, Northbrook, IL 60065-3293.) Return Undeliverable Canadian Addresses to: P.O. Box 122, Niagara Falls, ON L2E 6S4. We make portions of our subscriber list available to carefully screened companies that offer products and services that may be important for your work. If you do not want to receive those offers and/or information, please let us know by contacting us at List Services, Laser

Focus World, 98 Spit Brook Road, LL-1, Nashua, NH 03062.

GST No. 126813153 Publications Mail Agreement No. 40052420

Laser Focus World is a registered trademark. All rights reserved. No material may be reprinted.Bulk reprints can be ordered from Sharon MacLeod, PennWell, Laser Focus World,98 Spit Brook Road, LL-1, Nashua, NH 03062, tel. (603) 891-9224; FAX (603) 891-0574, Attn. Reprint Dept.; [email protected].

Amplifi cation Technologies ....................... 22

Apollo Instruments Inc. ............................. 34

Argyle International Inc. .............................37

Avantes BV ................................................. 59

B&W TEK .................................................... 58

BioPhotonic Solutions Inc. .........................18

Bristol Instruments .....................................10

BWT Beijing Ltd. ........................................ 36

Cambridge Technology ................................ 6

Cargille Laboratories ................................. 73

Castech Inc. ............................................... 38

Chunghwa Telecom Laboratories ............. 72

Coherent Inc. ............................................. 30

Continuum ................................................. 23

CVI Melles Griot ......................................... 29

Dilas Inc. .................................................... 25

Edmund Optics ........................................... 11

Electro Optical Products Corp. ............ 52, 54

Electro-Optics Technology ........................ 20

FEMTO Messtechnik GmbH ....................... 72

Fermionics Opto Technology ......................21

G-S Plastic Optics ...................................... 64

GSI Group Inc. .............................................47

Hellma USA .......................................... 24, 63

Laser Institute of America ......................... 44

Lee Laser Inc. .............................................14

Lightmachinery Inc. ..............................15, 37

Master Bond ...............................................67

Micro Laser Systems Inc. .......................... 34

Mightex Systems ....................................... 49

Nanoplus GmbH ......................................... 40

Newport Corp. ............ C2, 28, 43, 46, 71, C4

NM Laser Products Inc. ..............................24

Oclaro ..........................................................27

Ophir-Spiricon Inc. ......................... 19, 69, 73

Optical Building Blocks Corp. .................... C3

Optical Research Associates..................... 42

OptoSigma Corp................................... 12, 72

OSI Optoelectronics ....................................41

Photon Inc. ................................................. 53

PI (Physik Instrumente) L.P. ...................... 55

Pico Electronics ......................................... 60

Piezosystem Jena GmbH ............................67

Power Technology ........................................1

Precision Photonics ................................... 50

Qioptiq Imaging Solutions ........................... 8

RPMC ......................................................... 26

Spectra Systems ....................................... 73

SPIE Optics + Photonics ............................ 62

Stanford Research Systems ..................... 45

StockerYale Inc. ......................................... 43

Thermo Fisher Scientifi c ............................17

Thin Film Center Inc. .................................. 34

Toptica Photonics ................................. 71, 73

Tricor Systems ............................................71

Trumpf ...........................................................4

VLOC ............................................................16

Vuemetrix ....................................................21

Xi’an Focuslight Technologies Co., Ltd. .... 35

Zemax Development Corp. ........................ 32


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IN MY

VIEWB Y J E F F R E Y B A I R S T O W

Jeffrey Bairstow

Contributing Editor

[email protected]

The sayings of Rear Admiral Grace Murray Hopper, USNScanning the “New Arrivals”

shelf of my local library recently, I was

very pleasantly surprised to come across

an intriguing new book by Professor Kurt

Beyer: Grace Hopper and the Inven-

tion of the Information Age [MIT Press,

Cambridge, MA (2009)]. I fi rst met the

then-Commander Grace Hopper, USN,

in Seattle where she gave the keynote

address at the History of Programming

Languages conference in June of 1978.

As I recollect, the meeting was standing-

room only, particularly in the sessions

where Grace Hopper participated.

The conference attendees frequently

referred to Grace Hopper as “Amazing

Grace.” Indeed, the numerous achieve-

ments of Grace Hopper in computer pro-

gramming were nothing short of amazing.

She had an outstanding career that encom-

passed military research and development,

academic research and teaching, and busi-

ness software design and development.

Professor Beyer has written quite an

interesting biography of this leading pio-

neer in computers and programming. He

details Hopper’s World War II assignment

by the US Navy to the Harvard University

Computation Laboratory, the home of the

huge Mark 1 electromechanical calcula-

tor. At the end of the war, Hopper joined

Remington Rand, a typewriter company

that was developing computers for poten-

tial business use (the Univac series).

Despite the extensive male chauvin-

ism of that time, Hopper had unparalleled

opportunities to develop her own ideas

on computer programming. She also

honed her research and teaching skills.

Grace Hopper may not have been the

inventor of the Information Age, but she

certainly was a moving force in the rapid

development of computers and program-

ming languages for business applications.

Whenever Hopper “retired,” new

assignments were speedily offered and

were welcomed by Amazing Grace. She

was offi cially retired from the US Navy

in 1986 as the service’s oldest serv-

ing offi cer. She was promptly hired by

Digital Equipment Corporation, where

she worked until her death in 1992 at

the age of 86.

You’ll have to read the book to get

the full fl avor of the radical ideas and

machine-gun delivery of Grace Murray

Hopper. However, I thought I might

give you some of the observations that

poured forth from this diminutive Navy

person who always appeared in public in

her full dress Navy uniform.

(N.b. Grace Hopper’s original observa-

tions are in italics; the comments imme-

diately following each one are mine.)

On computing

Information is more valuable than the

hardware which processes it.

A situation that becomes even more

obvious as desktop and laptop comput-

ers become ever more ubiquitous.

Management versus leadership

You cannot manage men into battle.

You manage things; you lead people.

Both military forces and business

enterprises need strong leaders in

order to survive.

Getting things done

It is much easier to apologize

than it is to get permission.

Just as saying “No!” is much easier than

saying “Yes!” How often do we take the

easy route rather than the harder and

often riskier one?

Taking risks

A ship in port is safe but that is

not what ships are built for.

Spoken like the high-ranking naval

offi cer she was!

Pushing the envelope

At any moment there is always a line

representing what your boss will believe.

Go as close to that line as possible.

Defi nitely words to live your business

life by!

If you’d like to hear more wisdom

from Grace Hopper, try YouTube (www.

youtube.com), where you can fi nd sev-

eral videos featuring her. Look for a very

entertaining interview by Dave Letterman.Grace Hopper may not have

been the inventor of the

Information Age, but she

certainly was a moving force

in the rapid development of

computers and programming

languages.


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