Laser Source for the - Collider

Jim EarlyLawrence Livermore National LabLaser Science and Technology

SPLATShort Pulse Lasers,

Applications & Technology

Presented to: Snowmass 2001 July 6, 2001

Requirements for gamma-gamma laser LLNL

• Efficient conversion of electron energy to photons requires:

- laser wavelength near 1m

- laser pulse duration near 2ps to overlap electron pulse

- 1J per subpulse in high quality beam for adequate photon density in

conversion zone

- laser pulse format matching electron accelerator

• Low duty factor and short pulse duration requires use of “storage” laser

- solid state storage lasers used in laser fusion program give ns pulses

- thermal management of high average power a challenge in solid lasers

• Optical compression required to avoid damage in laser amplifier

- pulse must be stretched from several ps to several ns before amplifier

- chirp pulse stretching and compression technique required

Laser architecture driven by electron bunch format

96 pulses1J, 2ps, 1 m

3ns spacing

120 Hz macro-pulses

• 100 J macro-pulses require large “storage” laser amplifier

• Amplifier thermal design leads to low, 10 Hz, laser pulse rate

- 12 amplifiers use simple spatial combiner to achieve 120 Hz

• DOE Inertial Fusion Energy program developing “Mercury” laser that

meets requirements

• Optical design breaks 100 J macro-pulse into train of 1 J sub-pulses

laser system architecture: CPA front endseeds 12 Mercury power amplifiers

Mode-lockedoscillator

Spectral shaper

Stretcher OP-CPApreamp

Mercury power ampMercury power amp

Mercury power amp

Beamsplitters

12- 100 J power amplifiers

Optics:Combiner, splitters

Grating compressor 100 J macropulse:100X 2ps micropulses120 Hz

0.5 J3 ns120 Hz

Goals:• 100 J • 10 Hz• 10% electrical • 2-10 ns

The Mercury laser will utilize three key technologies: gas cooling, diodes, and Yb:S-FAP crystals

vacuum relay

gas-cooledamplifier head

Injection and reversor

Architecture: - 2 amplifier heads - angular multiplexing - 4 pass- relay imaging - wavefront correction

front end

DM

Pump delivery

Front end

Injection multi-pass spatial filter

Diode pulsers

Gas-cooled amplifier head

Milestone budget breakout:

1. $3030k Build two pump delivery systems

2. $1800k Fabricate Yb:S-FAP crystals

3. $825k Design and build wedged amplifier head

4. $1025k Build injection and reverser hardware

5. $1270k Integrated tests and code benchmarking

6. $300k Advanced Yb:S-FAP growth

7. $350k (LLE) Spectral sculpting experiments and evaluation of

average-power frequency conversion design

Mercury project FY01 funding from IFE program

We are on schedule to build half Mercury in FY01.FY02 funding will be slight increase.

We are on schedule to build half Mercury in FY01.FY02 funding will be slight increase.

Objective 1: Build two pump delivery systems

beam

diode package on split backplanes

gas-cooledamplifier head

vacuumenclosure

pump duct and homogenizer

Goal

Status

• 80 V-BASIS 23-bar 900 nm tiles fabricated

• Two functioning backplanes loaded with diodes

• Remaining power supplies/pulsers purchased

• Pump delivery hardware assembled, integrated, and currently being activated

The Mercury diodes deliver the pump light toYb:S-FAP crystals

Half array is madeof 5x7 =35 tiles

Full array 161 kW

4 pairs of half arrayslike these are requiredfor Mercury 644 kW

.

diode

v-sp

ring

Si submount

Mo block

Si lensframe

mic

role

ns

55°

Each tile is madeof 23 diode bars

2.3kW

Diode light distribution (green) obtained in a plane normal to the optical axis

7 tiles

5 tiles

The V-BASIS packaged diode bars meet the optical specifications of the Mercury Laser System

1 full backplane array (72Mounted tiles) complete

5% droop demonstrated

44% demonstrated

Completed Fabrication of 80 tiles

StatusRequirement

Demonstrated 3.7 nm FWHM on tiles for one split backplane

Pulse integratedLinewidth < 8.5 nm FWHM

Assemble tiles onsplit backplane

Power droop duringpulse < 15%

Testing is ongoing, butcurrently demonstrated1.4 x 108 shots without problems

Reliability of> 2 x 108 shots

45% electrical toOptical efficiency

115 W peak / 1 cm bar demonstrated with good lifetime

100 W peak /1 cm bar

104

103

102

101

1

0.1 88 90 92 94 96 98 00 02

Copper Heat Sinks

Microchannel Cooled Bars

Microchannel Cooled Monolithic Arrays

CW Bars

Peak Power Bars

Sources: L&O Market Survey 10/93L&O Market Survey 11/95LLNL/USEC Survey 96

Year

$ /W

att

Laser Focus World 2/98Purchase Order 99Quotation for 00 deliveryD. Scifres (SDL) CLEO ‘99

Similar to other integrated circuit technology, the cost of diode arrays has been dropping even while the performance has been increasing

Heliumgas

Slabmetalvanes

Channelsection

Diffusersection

Nozzlesection

Edge claddingWindow

Gas cooled head and vanes

1/8

0

0.1 Machgas flow

4 atmpressure

static

Pressure and gas flow contributes 1/16 wave to wavefront distortion

Fabrication of Yb:S-FAP crystals

Goal A full size 4x6 cm amplifier slab

Two 3x5 cm slabs Status

• One full size bonded amplifier slab completed - awaiting polish and AR coating

• Two smaller slabs (usable) also completed and await finishing

• Processes are not completely reproducible at this point

A axis

4 cm

6 cm

C axis

Crystals of Yb:S-FAP are grown by using theCzochralski (CZ) Method

Appropriate spectral sculpting of the input pulse can lead to a linearly chirped gaussian output pulse (2 psec stretched output pulse case)

RJB/VG 3-Oct-00 short Pulse Mercury Laser

Extraction Pulse Temporal Profile

0.0E+00

5.0E+09

1.0E+10

1.5E+10

2.0E+10

2.5E+10

3.0E+10

3.5E+10

4.0E+10

-8.E-09 -6.E-09 -4.E-09 -2.E-09 0.E+00 2.E-09 4.E-09 6.E-09 8.E-09

(sec)

(W)

Pass 4 (output)Pass 3Pass 2Pass 1Input Pulse

Normalized Emission Line and Saturated Gain for Yb:S-FAP

00.10.20.30.40.50.60.70.80.9

1

1035 1040 1045 1050 1055 1060

nm

Input Pulse Temporal Profile

0.0E+00

1.0E+06

2.0E+06

3.0E+06

4.0E+06

5.0E+06

6.0E+06

7.0E+06

8.0E+06

9.0E+06

-8.E-09 -6.E-09 -4.E-09 -2.E-09 0.E+00 2.E-09 4.E-09 6.E-09 8.E-09

(sec)

(W)

Telephoto ImagingSystem

LCM Light Valve

• Gratings: 1740 grooves/mm

• Telephoto imaging system EFL ~ 800 mm

A compact spectral sculptor using a liquid-crystal modulator light valve has been demonstrated

GratingGrating

Inte

nsi

ty

Original FM

Sculpted

0 100 200-100-200

Frequency (GHz)

Inte

nsi

ty

Original FM

Sculpted

0 100 200-100-200

Frequency (GHz)

0 100 200-100-200

Frequency (GHz)

8 May 1999

New technology enables production of Terawatt to Petawatt (1000 TW) pulses

Stretcher and compressor gratings LLNL

Stretcher CompressorSubstrate material silica silicaCoating material gold Multi-layerGrating size (cm) 4 x 15 30 x 84Roof mirror size (cm) 4 x 8 (flat) 30 x 40Grating separation (m) 5 15Lines per mm 1740 1740Laser beam diameter (cm) 1 10Cut bandwidth (nm) 2.0 2.0Exit sub-pulse duration (ps) 3000 2.2Efficiency-single bounce (%) 90. 96.0System efficiency (%) 60 80Laser macro-pulse fluence (J/cm2) 10-7 1.3Damage fluence (J/cm2) 0.4 2.0Approximate cost ($K) 20 1400

94 cm aperature gold coated diffraction Multilayer dielectric dielectric gratinggrating used for pulse compression designs of high-index (H) and low-index (L)on the Petawatt laser layers and groove corrugations (G).

1.00.80.60.40.20.0 -80 -40 0 40 8

0

Amplified pulseautocorrelation

44 fs = 31 fsdeconvolved

Time (fs)

=0.43

Vacuum compressor

0.6 J; 30 fs @ 1 Hz

20 fs Ti:sapphireoscillator

Pulsestretcher

regenerative amplifier: G=10 7

4-pass amplifier: G=40

4-pass amplifier: G=10

3-pass amplifier

45 mJ pump @ 10Hz

280 mJ pump@ 10Hz

1.5 J pump@ 10Hz

4 J pump@ 1Hz

Periscope tolinac caves

Planned upgradeto >7 J

Typical high-power CPA systems use multipleAmplifier stages to obtain gains of 1011

Optical parametric amplification is based on difference frequency generation

NONLINEAR CRYSTAL

signal

idler

PUMPLASER

short wavelength pump pulse

stretched long wavelengthseed pulse

p

s

i= p- s

ks ki

kp

k

pis kkk

pis

residual pump

600 mJ pump,532 nm, 8.5 ns

500 pJ seed,1054 nm, 3 ns BBO

preamplifier

vacuum relay telescope I

vacuum relay telescope II

15 %BS

90 mJ

420 mJ

BBO poweramp WP

WP

TFP

TFP

to compressor

31 mJ

0.1 TW-scale OPCPA was demonstrated as a full replacement for regenerative amplifier LLNL

beam splitter optical delay line

polarizerwave plate

• 100 J macro-pulse from laser converted to train of 1 J subpulses

• Combination of beam splitters and optical delay lines gives two beams

with string of pulses

• Two beams combined on polarizer to give single beam

- alternating linear polarization in pulses

- 96 pulses ( 3 x 25 )

Optical Pulse Train Generation LLNL

Gamma-gamma laser system cost estimate ($01) LLNL

• Capital costs $M

20 lasers

40 diodes (at $5/W)

10 optics system

20 building

20 development program

_40_ contingency

$150M total

• Operating costs $M/y

8 diodes at $5/W (5y or 109 shot lifetime)

4 labor

4 power

_4_ contingency

$20M/y

Gamma-gamma laser summary LLNL

• Pulse format of 1m - laser must match electron bunch format

• Mercury laser amplifier under development by DOE can serve as - laser

- laser under construction with single head to be completed in FY01

• New front end for Mercury laser will generate input pulse format needed

• Optical Compression Amplification and use of pulse string generation

optics can modify Mercury pulse format to - requirements

DOE Mercury laser project can serve as the demonstration prototype for the - laser project