GARPUNGARPUN--MTW: A Combined MTW: A Combined SubpicosecondSubpicosecond/Nanosecond /Nanosecond Ti:SapphireTi:Sapphire/KrF /KrF

Laser FacilityLaser FacilityPresented by: Vladimir D. Zvorykin1

Participants: S.V. Arlantsev2, N.V. Didenko3, A.A. Ionin1, A.V. Konyashchenko1,A.O. Levchenko1, O.N. Krokhin1, G.A. Mesyats1, A.O. Mavritskii3,A.G. Molchanov1, M.A. Rogulev1, L.V. Seleznev1, D.V. Sinitsyn1, S.Y. Tenyakov3,N.N. Ustinovskii1

1P.N. Lebedev Physical Institute of Russian Academy of Sciences, Leninsky pr. 53, 119991 Moscow, Russia2OKB “Granat”, Volokolamskoe sh. 95, 123424 Moscow, Russia

3Avesta Project Ltd., Solnechnaya st. 12, 142190 Troitsk, Moscow region, Russia

3rd Int. Conf. on the Frontiers of Plasma Physics and Technology FFPT-3, March 5-9, 2007. Bangkok, Thailand

ContentsContents

• Historical notes and motivation• Ti:Sapphire front-end• GARPUN e-beam-pumped facility • Numerical simulations and predictions• Conclusions

Historical notes and motivationHistorical notes and motivationNon-linear processes is the main restriction in MOPA schemes with direct amplification of short

pulses. In the 80-90-s KrF lasers had an advantage over solid-state amplifiers. The shortest pulses amplified in KrF laser were 60 fs [S. Szatmári & F.P. Schafer, Opt. Comm., 68, 196 (1988)] and the highest power up to 10 TW was achieved in RAL with KrF large-aperture e-beam-pumped amplifier with expected focused intensities as high as 1020 W/cm2 [E.J. Divall, et al., J. Mod. Opt., 43, 1025 (1996)].

A rapid progress in CPA technique in combination with OPA in non-linear crystals by today provides most experimental needs. PW laser channels are constructed and projected at the biggest ICF glass facilities NIF (LLNL, USA), Omega (UR LLE, USA), Vulcan (RAL, UK), GekkoXII (ILE, Japan), LMJ (France), ISKRA-6 (Russia) etc. to ignite thermonuclear fuel preliminary compressed by nanosecond pulses. 1000x increased neutron yields and >20% energy coupling to the cone target design was demonstrated.

Investigations of both laser physics and laser-plasma interaction during two past decades at 0.1-10.0 kJ-class single-shot KrF facilities Aurora (LANL, USA), Nike (NRL, USA), Sprite (RAL, UK), ASHURA (AIS&T, Japan) and GARPUN (LPI, Russia) and especially at rep-rate Electra laser (NRL, USA) have proved that e-beam-pumped KrF laser might be the best challenge for the direct-drive ICF power plant. Only DPSS laser could compete with KrF laser as a future reactor driver.

We are going to regenerate an interest to short-pulse amplification in large-aperture e-beam-pumped KrF amplifiers and to verify the fast-ignition ICF concept utilizing KrF drivers that could simultaneously amplify both long laser pulses for pellet compression and short pulses for ignition [V.D. Zvorykin, et al., Bull. of Lebedev Phys. Inst., No. 9-10, 20 (1997)]. The reported work is a first step of Petawatt Excimer Laser Project started at Lebedev Institute.

MainAmplifier(s)

(30-60 kJ) each 50 m

Driver Amp(2000 J)

Multiplexing optics TurningArrays

Chamber

Targetinjector

Front End(100 J) 100 m

Long optical paths enclosed in He or vacuum

Inertial Fusion Energy power plant with KrF laser driverInertial Fusion Energy power plant with KrF laser driver

Requirements for laser: total energy - 2.4 MJ; rep rate– 5 Hz; efficiency- 7.5 % Intrinsic efficiency of energy extraction should be about 12 %

Designed by the NRLDesigned by the NRL

UV laserUV laser--target interactiontarget interaction

1 mm1 mm

Shock waveShock wave

CraterCrater

Laser BeamLaser Beamqq=5=5*10*101212W/cmW/cm22

ττpp=100 ns=100 ns

0.5 mm0.5 mm

Properties of KrF moleculeProperties of KrF molecule

Potential-energy diagram of KrF molecule

Wavelength λ = 248 nmBandwidth ∆ν ≈ 200 cm-1

Radiation lifetime τr = 6.5 nsCollisional lifetime τc = 2 nsGain cross section σ= 2.5 10-16 см2

Saturation intensity Is = hν/στ ≈1 MW/cm2

Saturation energy Qs = hν/σ ≈ 2 mJ/ cm2

Intrinsic efficiency η ≈ 10%

ASE and shortASE and short--pulse amplificationpulse amplification

For long pulses τp ≥ τcand ASE:

⎥⎦

⎤⎢⎣

⎡−⎟

⎠⎞

⎜⎝⎛==

Ω+−

+= 1,/,

4/1

2/10

00

ασ

πτνα gIIgNNhI

IIgI

dxdI

soptrs

( )LgGAfAGIIS

ASE

r

cs

tASE 0

2# exp,41,/ =⎟⎟

⎠

⎞⎜⎜⎝

⎛∆∆

⎟⎟⎠

⎞⎜⎜⎝

⎛==

νν

ττ

π

For short pulses τp<< τc: ( )[ ]α

εαεεε 00 ln,/,exp1 gQQQQg

dxd

sopts ==−−−=

( ) ,/ 2#θτ fBQI pstp =

5410927

4#40

1010,1010,/10~:500100,100

,10,1,10~,42,006.0,24.0,2010

÷=÷=−==

==÷===∆

∆÷= −

QItASEppump

S

ASE

CRCRcmWIfsns

radfGBAg

ττ

θνα

Contrast ratio (intensity):2

/θττ

GABCR pc

I = Contrast ratio (energy):2

/θττ

GABCR pumpc

Q =

Intensity on target:

Intensity on target:

To keep the ASE and CR at a suitable level one should increase a seed pulse and restrict a total gain in KrF amplifier chain. To reduce g0 it is possible to work at low gas pressure (≤ 1 atm) or to load amplifiers by a continuous train of ns pulses.

Layout of short & long pulses amplification in KrF Layout of short & long pulses amplification in KrF amplifiersamplifiers

EMG 150 master oscillator: 0.2J, 20 ns, 80 Hz, 0.2 mradGeneral view

GARPUN e-beam-pumped amplifier: 16*18*100 cm, 100J, 100 ns, ~0.1mrad

Berdysh e-beam-pumped preamplifier: 10*10*100 cm, 25J, 100 ns, 0.1 mrad

GARPUN KrF GARPUN KrF LaserLaser FacilityFacility

EMG 150 master oscillator: 0.2J, 20 ns, 80 Hz, 0.2 mradGeneral view

GARPUN e-beam-pumped amplifier: 16*18*100 cm, 100J, 100 ns, ~0.1mrad

Berdysh e-beam-pumped preamplifier: 10*10*100 cm, 25J, 100 ns, 0.1 mrad

GARPUN KrF GARPUN KrF LaserLaser FacilityFacility

FINAL KrF LASER AMPLIFIERFINAL KrF LASER AMPLIFIERFront view of DM 60Front view of DM 60--cm diameter and 200cm diameter and 200--cmcm--longlong amplified amplified pumped pumped byby radiallyradially convergent econvergent e--beamsbeams

HighHigh--voltage power supply and synchronization voltage power supply and synchronization scheme of GARPUN facilityscheme of GARPUN facility

PFLs produce 350-kV, 100-ns accelerating pulses applied to cathodes in vacuum diodes

Laser pulses of master oscillator synchronize switches of all PFLs

Monte Carlo Algorithm for eMonte Carlo Algorithm for e--beam transport through beam transport through the matterthe matter

'

0

( '') ''

0

, ,2 21 /

' ( ') ,

(0,1);

S

S Q s ds

t

md eedt v cddt

ds Q s e

Q N

ξ

ξ σ

⎡ ⎤⎢ ⎥− ⋅⎢ ⎥⎣ ⎦

⎡ ⎤= ⋅ ⋅ =⎣ ⎦−

=

∫⋅ ⋅ =

∈ =

∫

vP v B P

S v

rurr ur ur

rr

(1)

(2)

e-beam e-beam

1

2

3

4

5

6

7

8

9

Cross section of GARPUN laser

22

2 2 2 2 2

1 1 (2 1) 12 (1 ) ( 1) (1 ) ( 1)

ine

d Z T Trd T T Tσ πε β ε ε ε ε

⎡ ⎤+= − ⋅ + +⎢ ⎥− + − +⎣ ⎦

22

2 2 2

22

21/ 3

(1 2 cos )

( 1)1.13 3.76 ( /137)( 2)

137 0.885 4 ( 2)

el e

e

d rZd p

TZZ T T

T T

σβ η θ

η

=Ω + −

++ ⋅ ⋅⎛ ⎞ += ⋅⎜ ⎟⋅ +⎝ ⎠

2 2

2 2 2

( 2) / 8 1 (2 1) ln 20.3056 ln[ ]2 ( 1)

dT Z T T T TdS A I T

ρβ

⎧ ⎫+ + − += ⋅ ⋅ +⎨ ⎬+⎩ ⎭

Moliere expression

Rutherford expression

Bethe-Bloch equation

(4)

(5)

(3)

Monte Carlo code calculating eMonte Carlo code calculating e--beam transportbeam transport

Simulation of energy deposition in GARPUN laser chamber

Energy deposition vs gas pressure (Garpun, Ar)

0

500

1000

1500

2000

2500

0 0,5 1 1,5 2 2,5 3

Pressure, atm

Ener

gy, J

with reflections from diodes(Transp=1)without reflections (Transp=0)

with reflections (Transp=0.6)

experimental data (Ar)

Distribution of specific pumping energy over GARPUN laser chamber filled with Ar at 1.75-atm pressure

0,95-10,9-0,950,85-0,90,8-0,850,75-0,80,7-0,750,65-0,70,6-0,650,55-0,60,5-0,550,45-0,50,4-0,450,35-0,40,3-0,350,25-0,30,2-0,250,15-0,20,1-0,150,05-0,10-0,05

1

10

19Р1 Р5 Р9

Р13

Р17

Распределение энерговклада в сечении камеры (Гарпун) 0.95-1

0.9-0.950.85-0.90.8-0.850.75-0.80.7-0.750.65-0.70.6-0.650.55-0.60.5-0.550.45-0.50.4-0.450.35-0.40.3-0.350.25-0.30.2-0.250.15-0.20.1-0.150.05-0.10-0.05

Quasistationary KrF laser codeQuasistationary KrF laser code

NonNon--stationary Monte Carlo codestationary Monte Carlo code)()( *

212122

22 ρτ

⋅+⋅−−= BANN

tPdt

dN)( 21212 ρνρ

⋅⋅+⋅= hfBANdtd

( ) 1

62542

322

12

−+++++= KrFeKrArKrAr NkNkNkNkNNkNkτ

Comparison of experiments and simulationsComparison of experiments and simulations

Calculation of ASE in GARPUN amplifierCalculation of ASE in GARPUN amplifier

ASE measurements in GARPUN amplifierASE measurements in GARPUN amplifier

1

72 3

4

9

6 5

810

11

12

Experimentalconditions:pumping &

configuration

Measured values Values recalculated tothe boundary

Simulatedvalues

Energydensity,mJ/cm2

Intensity

MW/cm2

Energydensity, mJ/cm2

Intensity

MW/cm2

Intensity

MW/cm2

Full pumping &single-pass 6.5 0.16 22.8 0.56 0.63

Full pumping &double-pass 66.4 1.64 188 4.64 5.2

Half pumping &single-pass 2.0 0.05 7.0 0.18 -

Half pumping &double-pass 3.5 0.086 9.9 0.24 -

= 1.4×102 J/srΩd

dEASE

= 3.5×109 W/srΩd

dWASE

0 20 40 60 80 100 120 140 160 180 200 220Time, ns

Inte

nsity

, rel

. uni

ts

1

0.5

0

Ti:Sapphire frontTi:Sapphire front--end end ““StartStart--248M248M””

Facility occupies standard 1200*3000 mm2 lab table. Ti:Sapphire oscillator with pumping laser (λ=532 nm), all-reflected-optics grating stretcher and compressor, regenerative amplifier are all enclosed in a common 600*1100 mm2 box.

Block diagram of Ti:SapphireBlock diagram of Ti:Sapphire laser systemlaser system

“Start-248M” consists of Ti:Sapphire oscillator TiS-20 with 4-W CW Finesse 532 DPSS pumping laser (λ=532 nm), grating stretcher and compressor, regenerative amplifier and multi-pass amplifiers pumped by pulsed Nd:YAG LS-2134 laser (2*100 mJ@532 nm), 3-ωfrequency converter, 1-ω and 3-ω spectrometers ASP.

Optical Scheme of “Start-248 M”

PR

Pm1

OC

L

M1

M3

M2

M6 M5

M4

P1

P2 S A2

TiS

M7

A3

A1

TISTIS--20 master oscillator20 master oscillatorf =80 MHz, W = 0.2-0.3 W,∆λ~30 nm, τp=30 fs

Regenerative amplifier Regenerative amplifier

CompressorCompressor

Optical scheme of 5Optical scheme of 5--pass amplifierpass amplifier

Output energy ≥15 mJ

Ti:Sapphire frontTi:Sapphire front--end end ““StartStart--248 M248 M”” was was installed and characterizedinstalled and characterized

SYSTEM PARAMETERS

Repetition rate 0-10 HzPulse width at λ=744 nm < 50 fsPulse width at λ=248 nm < 60 fsPulse energy (@ 10 Hz) at λ=744 nm > 8 mJPulse energy (@ 10 Hz) at λ=248 nm > 0.5 mJBeam diameter at λ=744 nm 10 mmBeam diameter at λ=248 nm 8 mmStability of energy at λ=744 nm < 3%Stability of energy at λ=248 nm < 5%

Fs pulse of Ti:Sapphire frontFs pulse of Ti:Sapphire front--end was synchronized end was synchronized and amplified in the dischargeand amplified in the discharge--pumped pumped KrFKrF amplifieramplifier

In pilot experiments fs pulse was amplified in double-pass discharge-pumped KrF amplifier with a gain factor of 5 with output energy of ~1.5 mJ and Q= 6.5 J/cm2, which is 3.25 times more than saturation energy density Qs.

Long & short pulses amplification in Long & short pulses amplification in BerdyshBerdysh

0 0( )(1 ) ( ) , 0fdf g x e a x f x Ldx

= − − < <

Long & short pulses amplification in GARPUNLong & short pulses amplification in GARPUN

0 0( )(1 ) ( ) , 0fdf g x e a x f x Ldx

= − − < <

Long & short pulses amplification in DMLong & short pulses amplification in DM

With the projected 60-cm-aperture, 200-cm-long DM amplifier 18 J energy in a single short pulse is expected on a par with 4 kJ in 250-ns train of long pulses amplified with a stage gain M≈ 20 and intrinsic efficiency η eff ≈10%. The contrast ratio of short-pulse intensity on a target to the ASE is expected in the range 2⋅108÷3⋅109.

Parameters of Parameters of excimerexcimer moleculesmolecules

0.0020.20.04Qsat, J/cm2

2.5×10-162.3×10-1810-17σ, cm2

6 180100 τr, ns

40712.5τ lim, fs

5 80 60 ∆λ, nm

248 405 474 λmax, nm

KrF (B→X)Kr2F(4 2Γ→1,2 2Γ)XeF(C→A)Transition

Layout of fluorescence and absorption Layout of fluorescence and absorption measurements at measurements at BerdyshBerdysh laser modulelaser module

CapillaryCapillary--discharge discharge light source for absorption light source for absorption measurements and calibration of wavelength responsemeasurements and calibration of wavelength response

( ) 12

5

2

−=

bTkhchcBλλλ /exp

Tb = 39±2 kK

Spectral brightness of light source:

Fluorescence spectra of Ar/Kr/FFluorescence spectra of Ar/Kr/F22 mixturesmixtures

Gas mixture Ar/Kr/F2 = 0.3/8.9/91.8% at p = 1.8 atm under e-beam excitation presents fluorescence bands of KrF (B→X), KrF (C→A), and Kr2F(42Γ→1,2 2Γ).Using these spectra small-signal gain coefficient g0Kr2F ~0,002 cm-1 was found.

Transient absorption spectra ofTransient absorption spectra of Ar/Kr/FAr/Kr/F22mixturesmixtures

Absorption spectrum of Ar/Kr/F2 = 0.3/8.9/91.8% gas mixture at p = 1.8 atmdemonstrates bond-bond transitions by transient species and broad continues band of photodissociation of Kr2F (42Γ) molecule. Dashed line is the spectrum measured by Schloss et al, J. Chem. Phys., 106 (13), 5423, (1997).

SUMMARYSUMMARYThe first step of Petawatt Excimer Laser Program was

started at P.N. Lebedev Physical Institute. Multi-terawatt hybrid Ti:Sapphire/KrF laser system is currently under development for combined laser-plasma interaction studies and verification of the fast-ignition KrF laser scheme utilizing simultaneous amplification of both short (ps) and long (ns) laser pulses in the same e-beam-pumped modules.

ACKNOWLEDGMENTS

This research was implemented within the Programs of the Russian Academy of Sciences “Fundamental problems of relativistic pulsed and stationary high-power electronics” and “Femtosecond optics and new optical materials”. It was supported also by Russian Ministry of Science and Education, and US Naval Research Laboratory.