prospects of thz pulse generation with mj- l l e d 100 mv

Department of ExperimentalPhysicsPhysics

http://physics.ttk.pte.hu

Prospects of THz Pulse Generation with mJ-L l E d 100 MV/ El t i Fi ldLevel Energy and 100 MV/cm Electric Field

J A Fülöp1,2,* Z Ollmann3 L Pálfalvi3 G Almási1,3J.A. Fülöp , , , Z. Ollmann , L. Pálfalvi , G. Almási , ,J. Hebling1,3

1High-Field THz Research Group HAS HungaryHigh Field THz Research Group, HAS, Hungary2Attosecond Light Pulse Source of the Extreme Light Infrastructure, Hungary

3Department of Experimental Physics, University of Pécs, Hungary

*e mail: fulop@fizika ttk pte hue-mail: [email protected]

Workshop on THz Sources for Time Resolved Studies of Matter, ANL, Argonne, July 30-31, 2012

Applications of High-Energy THz Pulses

0,6

0,8

1,01,0

ampl

itude

(a. u

.)

.)

Emax

0 1 2 30,0

0,2

0,4

0 0

0,5

Spe

ctra

l a

Frequency (THz)

tric

field

(a. u

.

-0,5

0,0El

ect

Linear THz spectroscopy (E ≈ 100 V/cm → 10 fJ pulse energy)

-2 0 2 4 6 8time (ps)

Linear THz spectroscopy (Emax ≈ 100 V/cm → 10 fJ pulse energy) graphene, nanotubes, molecular magnets, etc.

N li TH t (E 100 kV/ J l )Nonlinear THz spectroscopy (Emax ≈ 100 kV/cm → µJ pulse energy)THz pump – THz probe measurements of dynamics (Hoffmann et al., PRB, 2009)

Manipulation and acceleration of charged particlesManipulation and acceleration of charged particles(Emax ≈ 100 MV/cm → 10 mJ pulse energy)VUV–XUV pulse generation by Thomson-scattering, X-ray free electron laser, …

Optical Rectification

[ ][ ]2

THz2

232

22eff

2THz

THz 44sinh2

THz

LLeILd L α

εωη α ⋅⋅= −

Conversionefficiency

[ ]THz3

THz2

0 4Lcnnv αεdepends on:

THz frequency: 2THzTHz ωη ∝

h

Material parameters → FOM

THzTHzη

phTHz

grvis vv =Phase matching → velocity matching:

L << 12222 ILdeffω

η eff LdFOM

22

Figure of merit (FOM):

αTHzL << 1 320 cnn THzv

ffTHz ε

η =

228 Ideffω

THzv

ffNA nn

FOM 2=

24 ffdαTHzL >> 1 322

0

8cnn

d

THzTHzv

effTHz αε

ωη = 22

4

THzTHzv

effA nn

dFOM

α=

Materials for Optical Rectification

Material deff( /V) ( 1)

FOM*( 2 2/V2)

grnmn800 THn

grmn μ55.1

THzα(pm/V) (cm-1) (pm2cm2/V2)

CdTe 81.8 3.24 2.81 4.8 11.0

nm800 THzn μ

GaAs 65.6 4.18 3.59 3.56 0.5 4.21

G P 24 8 3 67 3 34 3 16 0 2 0 72GaP 24.8 3.67 3.34 3.16 0.2 0.72

ZnTe 68.5 3.13 3.17 2.81 1.3 7.27

GaSe 28.0 3.13 3.27 2.82 0.5 1.18

sLiNbO3sLN 100K

168 2.25 4.96 2.18 174.8

18.248.6sLN 100K 8 8 6

DAST 615 3.39 2.58 2.25 50 41.5

Velocity matching condition: THzgrNIR

phTHz

grNIR nnvv =⇒=

* for L = 2 mm

Tilted-Pulse-Front Pumping (TPFP)

phTHz

grvis cos vv =⋅ γ

~100 fs typicalHebling et al., Opt. Express, 2002

Tilted-Pulse-Front Pumping vs. Line Focusing

Stepanov et al., Opt. Express, 2005 Hoffmann & Fülöp, J. Phys. D, 2011

THz Pulse Generation by Optical Rectification in LiNbO Using Tilted Pulse Front Pumping

Large nonlinear coefficient (deff = 168 pm/V)

LiNbO3 Using Tilted Pulse Front Pumping

Velocity matching by tilting the pump pulse front

Hebling et al Opt E press 2002phgr Hebling et al., Opt. Express, 2002

Highest THz pulse energy from a table-top source0 25 μJ Stepanov et al Opt Express 2005

phTHz

grvis cos vv =⋅ γ

0.25 μJ Stepanov et al., Opt. Express, 200510 μJ Yeh et al., Appl. Phys. Lett., 200750 μJ Stepanov et al., Appl. Phys. B, 2010

125 J Fülö t l O t L tt 2012125 μJ Fülöp et al., Opt. Lett., 2012

Further increase of THz energy is in sightti l diti – optimal conditions

(pump pulse duration & wavelength, crystal temperature & length)Fülöp et al., Opt. Express, 2011

– by increasing the pumped area in optimized setupsPálfalvi et al., Appl. Phys. Lett., 2008Fülöp et al., Opt. Express, 2010

Effective Interaction Length

-20 -10 0 10 20

Pump propagation distance, ζ [mm]

ps]

εdnPulse front tilt:

2

dura

tion,

τ [p (a)

λελγddtan

gnn

−=

1

Pum

p pu

lse

d

2Ld

materialdispersion

angular dispersionLiNbO3

[%]

0 τ0 = 50 fsτ = 350 fs

P

GVD parameter:

dispersiondispersionLiNbO3λp = 800 nm

Fp = 5.1 mJ/cm2

Ωpm = 1 THz

( )⎥⎦

⎤⎢⎣

⎡−⎟

⎠⎞

⎜⎝⎛==

−

2

221

λλελ

λ dnd

ddn

cdvd

D g

4

(b) Ln ef

ficie

ncy

[ τ0 350 fs τ0 = 600 fs

⎦⎣ ⎠⎝ λλλ ddcd2

(b) Leff

Hz

gene

ratio

n

Martínez et al JOSA A 1984-5 0 5

0

THz propagation distance, z [mm]

TH

Martínez et al., JOSA A, 1984Hebling, Opt. Quantum Electron., 1996Fülöp et al., Opt. Express, 2010

Effective Interaction Length

Limiting effect Possible solution

Change of pump pulse duration insidethe medium

Use longer Fourier-limited pump pulsesUse materials requiring smaller pulse-front tiltfront tilt

Absorption at THz frequenciesCool the crystal to reduce α

Absorption coefficient αMulti-photon absorption (MPA) of thepump

Cool the crystal to reduce αUse longer pump wavelength tosuppress low-order MPA

Use materials requiring smaller pulse-

Walk-offfront tiltUse large pump beam (and energy):→ Optimized imiganig systemp g g y→ Contatc grating (no imaging)

Optimization of the Pump Pulse Length

3.0LiNbO3

Fülöp et al., Opt. Express, 20113.0

2.5 300 K

[MV

/cm

] LiNbO3L ≤ 10 mmIp, max = 40 GW/cm2

λp = 1064 nm2.5

300 K 100 K 10 K

2.8 MV/cm

[MV

/cm

]

1 5

2.0

ric fi

eld

[ p

absorption 1 5

2.0

ric fi

eld

[

2.3 MV/cm

1.0

1.5

eak

elec

tr absorption coefficient of

LiNbO3:1.0

1.5

eak

elec

tr

0.5

240 kV/cm

1.0 MV/cmpe T [K] α [1/cm]

10 0.350.5

240 kV/cm

1.0 MV/cmpe

0 500 1000 15000.0

pump pulse duration [fs]

100 2.1

300 160 500 1000 1500

0.0


experimental value: 110 kV/cm Hoffmann et. al., Phys. Rev. B., 2009


300 K100 K

25 300 K100 K

10

y [

%]

100 K 10 K

15

20

y [

mJ]

100 K 10 K

5

effic

ienc

y

2.0%5

10

THz

ener

g

0 500 1000 15000

pump pulse duration [fs]0 500 1000 1500

0

pump pulse duration [fs]p p p [ ] p p p [ ]

τp = 500 fsEp = 200 mJI 40 GW/cm2

THz energy ≈ 25 mJ

THz field = 2.8 MV/cm (unfocused)

10 MV/cm level using imagingIp, max = 40 GW/cm2 → 10 MV/cm level using imaging

→ 100 MV/cm level using focusing


Frequency at the spectral peak

1,5 LiNbO3

L ≤ 10 mm 300 K 100 K 10 K

0 [T

Hz] Ip, max = 40 GW/cm2

lp = 1064 nm1,0

uenc

y, Ω

0

Phase matching adjusted to the

0,5

peak

freq

u

spectral peak

0 200 400 600 800 1000

p


New Appilcation Possibilities for THz Pulses with High Electric Field

TH

High Electric Field

THz beam

AccelerationAccelerationPlettner et al., Phys. Rev. Spec. Top. – Accel. and Beams 9, 111301 (2006)

Beam deflection, focusingPl tt t l Ph R S T A l d B 12 101302 (2009)

1 GV/m = 10 MV/cm peak field strength is needed

Plettner et al., Phys. Rev. Spec. Top. – Accel. and Beams 12, 101302 (2009)

New Appilcation Possibilities for THz Pulses with High Electric Field High Electric Field

Enhancement of HHGEnhancement of HHGE. Balogh et al., PRB, 2011K. Kovács et al., PRL, 2012

Longitudinal compression of electron bunches→ single-cycle MIR…XUV pulse generationHebling et al., arXiv:1109.6852Hebling et al., presentation on Monday

Electron undulationH bli t l Xi 1109 6852Hebling et al., arXiv:1109.6852

Proton acceleration(40 → 100 MeV requires 30 mJ THz energy)(40 → 100 MeV requires 30 mJ THz energy)→ hadron therapyPálfalvi et al., in preparation

Towards mJ Level THz Pulses: Experiment

In collaboration with S. Klingebiel, F. Krausz, S.

1000 experiment 1.6 power fitcalculation

KarschMPQ, Garching

100

calculation square law

y [

μJ]

Further possibilities:

• Optimal pump duration10

THz

ener

gy

T =300 K Optimal pump duration• Cooling the LiNbO3• Contact grating

1

T T =300 Klp = 1030 nm

tp = 1.3 ps (not Fourier-limited)1 10 100

1

pump pulse energy [mJ]

Fülöp et al., Opt. Lett. 2012:125 J

Comparison with earlier results:

Stepanov et. al., Appl. Phys. B, 2010:E 50 J 125 µJ

0.25%ETHz = 50 µJ η = 0.05%

×2.5

×5

THz Beam Profiles

1.0(a)

1.0(a)

Contact gratingNo limit for lateral

THzLNcrystal

4

0

2

-2

x [mm]

( )1.0

(a)

0 5

(a)

y[a

rb.u

.]

0 5

(a) (b)

y[a

rb.u

.]size

No imaging optics

Pálf l i t l APL 2008

-4

2

(c)pump

0 5

(a) (b) (c)

y[a

rb.u

.]

THzLNcrystal

pump

0.5

THz

inte

nsity

THzLNcrystal

pump

0.5

THz

inte

nsityPálfalvi et al., APL, 2008

Ollmann et al., APB,submitted

THzLNcrystal

pump

0.5

THz

inte

nsity

(a) -8-40480.0

T

x [mm]THz

(a) -8-40480.0

T

x [mm]

Non-optimized

Optimized THz

(a) -8-40480.0

T

x [mm]

pump

THz

2

m] 8E-4

1E-3

THz generation efficiency [arb. u.]

4

02

x [mm]Optimized

Grating image is tangential to pump

THz

2

m] 8E-4

1E-3

THz generation efficiency [arb. u.]

4

02

x [mm]

-2

0

ξ [m

m

0

2E-44E-4

6E-4

-4

0-2

pulse front

Longer focal length lens

-2

0

ξ [m

m

0

2E-44E-4

6E-4

-4

0-2

LN crystal-2 0 2

ζ [mm]4-4(b)

length lens

Fülöp et al., Opt. Express, 2010

LN crystal-2 0 2

ζ [mm]4-4(b)

Optimizing the TPFP Setup Containing Imaging

LiNbO3, λp = 800 nm

Fülöp et al Opt Express 2010

90 θi optimal angle of incidence

Fülöp et al., Opt. Express, 2010

60

ncid

ence

θLittrow

θLittrow+10θLittrow-10o

30

angl

e of

in

1200 1600 2000 24000

2200 1/mm

1/d (1/mm)

1800 1/mm

1/d (1/mm)

1 MV/cm field and 0 1% efficiency reached by applying our above results1 MV/cm field and 0.1% efficiency reached by applying our above resultsHirori et al., Appl. Phys. Lett., 2011

Design of Contact Grating on LiNbO3

Contact grating for THz generation proposed:

Index matching by glass:

R f ti i d t hi li id (RIML)

Pálfalvi et al., APL, 2008

Nagashima et al., Japan J. Appl. Phys., 2010

Oll t l APB b itt dRefractive index matching liquid (RIML):

Diffraction efficiency for order -1

Ollmann et al., APB, submitted

RIML for BK7, d = 350 nm pitch grating

THz Energy vs. Pump Energy

105

103

104

J)

LN (tilted pulse front)

101

102

LN (Yeh, 2008)ergy

(n

1

100

10 ( ) LN (Yeh, 2007) LN (Stepanov, 2005) LN (Stepanov, 2008)ul

se e

ne

10-2

10-1( p )

LN (Fülöp, 2012) ZnTe (Blanchard, 2007) ZnTe (Löffler, 2005)TH

z pu

10-4

10-3

( , )

ZnTe (collinear)

10 100 1000 10000 10000010

pump pulse energy (μJ)

Reconsidering Semiconductors for THz Generation

Materi-al

λp = 800 nm λp = 1064 nm λp = 1560 nmMPA γ MPA γ MPA γ MPA: lowest-order

ZnTe 2PA collinear 2PA 22.4° 3PA 28.6°

GaSe 2PA 16.5° 2PA 25.9° 3PA 30.2°

multi-photon pumpabsorptionγ : pulse-front tilt angle

1 Ω0 = 1 THz

LiNbO3 3PA 62.7° 4PA 63.4° 5PA 63.8°γ : pulse-front tilt angle

Fülöp et al

100

101]

Ω0 1 THzFülöp et al.,Opt. Express, 2010

Advantages:

10-2

10-1

cien

cy [%

Saturation in LiNbO :

Advantages:Pump spot diameter can be increased

4

10-3

Effi

c

ZnTe, 1560 nm, 80 K (β3 = 3.99x10-4 cm3 GW-2)

ZnTe, 1064 nmGaSe 1560 nm

in LiNbO3:Hoffmann et al., Opt. Express,

increased

Smaller tilt angle, resulting in longer

0,1 1 10 100

10-4

Pump intensity [GW cm-2]

GaSe, 1560 nm LN, 1064 nm

p2007effective length

Design of Contact Grating on ZnTe

Ollmann et al., in preparation

0.8sinusoidal profile 1 4

0.7pump wavelength:

1460 nm

sinusoidal profile

1.3

1.4

μm]

0.5

0.6 1560 nm 1700 nm

ffici

ency

1.2

g pe

riod

[μ

0.4E

f1.1 G

ratin

g

0 10 20 30 40 50 60

0.3

Angle of incidence AOI [°]

1.0

Angle of incidence, AOI [ ]

Pump: 1.5 µm wavelength, 5 cm beam diameter→ THz energy = 2.2 mJgy→ THz intensity = 630 GW/cm2 (focused)→ THz field ≈ 20 MV/cm (focused)

Summary

Single-cycle THz pulse generation with 100 MV/cm field and ~10 mJ energy is feasible around ~1 THzf b OR d b ffi i t DPSS lfrequency by OR pumped by efficient DPSS lasers

Optimization of the TPFP technique2.0

2.5

3.0

300 K 100 K 10 K

2.8 MV/cm

ld

[MV/

cm]

2.3 MV/cm

→ pump pulse duration: 500 fs optimal for LN→ low crystal temperature→ optimal crystal length

0 0

0.5

1.0

1.5

240 kV/cm

1.0 MV/cmpeak

ele

ctric

fie

p y g→ contact grating setup for LN and ZnTe

(extension of beam size)

P li i i t l lt

0 500 1000 15000.0


100

1000 experiment 1.6 power fit calculation square law

J]Preliminary experimental results:125 μJ energy, 0.25% efficiency (non optimised!)

New application possibilities: 1

10

100

THz

ener

gy

[μJ

New application possibilities:

→ nonlinear THz spectroscopy→ manipulation of electrons and ions

1 10 1001

pump pulse energy [mJ]

p

Acknowledgement: Hungarian Scientific Research Fund (OTKA), grant numbers 78262 and 101846, SROP-4.2.1.B-10/2/KONV-2010-0002, and hELIos ELI_09-01-2010-0013.

prospects of thz pulse generation with mj- l l e d 100 mv

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