1. Palaiseau - FRANCE
Spatio-Temporal Chirped Pulse Amplification for Avoiding Spectral Modifications in Ultra-Short Petawatt Lasers
C. Radier1,2, F. Giambruno1,3, C. Simon-Boisson2, V. Moro2, G. Chériaux1
1 LOA, Chemin de la Hunière, Palaiseau Cedex, France
2 TOSA-DSL, 2 Avenue Gay Lussac, Elancourt, France
3 ILE, CNRS, Ecole Polytechnique, ENSTA, Institut d’optique, Palaiseau Cedex, France

2. Context (1/2)
Generation of multi-tens of joules energy and several tens of femtoseconds duration pulses leading to petawatt peak power levels
Extremely high peak power pulses (10 PW) :
=> Vulcan laser 300 J / 30 fs (OPCPA) in LBO and KDP
=> Apollon-10P 150 J / 15 fs (CPA) in Ti:Sa
Management of the spectral energy distribution in terms of shape and bandwidth during their amplification process :
=> Temporal profile adapted to the high intensity interaction
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3. Context (2/2) OPCPA configuration in LBO / BBO / KDP :
Control of the spectrum (width and shape) by the angles in the non-linear crystal and by the pump (temporal profile and intensity)
CPA configuration in Ti:Sa :
Amplification of temporally chirped pulses
=> Gain narrowing (inhomogeneous spectral gain )
Input : Δλ½ = 85 nm
Pass 6 : Δλ½ = 62 nm
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Frantz et Nodvik model : « Gain regime : J0(t) ~ Jsat / 1000 & G = 100 » 

4. Context (2/2) OPCPA configuration in LBO / BBO / KDP :
Control of the spectrum (width and shape) by the angles in the non-linear crystal and by the pump (temporal profile and intensity)
CPA configuration in Ti:Sa :
Amplification of temporally chirped pulses
= Gain shifting (amplification saturation )
Input : λc = 794 nm
Pass 6 : λc = 808 nm
Duration (ps)
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Frantz et Nodvik model : « Saturation regime : J0(t) ~ Jsat / G = 1,8 » 

5. Existing solutions
Different relevant active and passive solutions to overcome the gain narrowing issue (mJ-level pulses in the 10 fs regime)
Acousto-optic programmable dispersive filter1
Multilayer Gain Narrowing compensators2,3,4
Negatively and Positively Chirped Pulsed Amplification5
No solution to suppress the spectral shape modifications due to saturation effects at moderate or high level energy (> 1J).
F. Verluise et al., “Amplitude and phase control of ultrashort pulses by use of an acousto-optic programmable dispersive filter: pulse compression and shaping”, Opt. Lett. 25, 575–577 (2000).
A. Amani Eilanlou et al., “Direct amplification of terawatt sub-10-fs pulses in a CPA system of Ti:sapphire laser,” Opt. Express 16, 13431–13438 (2008).
H. Takada, et al., “High-repetition-rate 12fs pulse amplification by a Ti:sapphire regenerative amplifier system,” Opt. Lett. 31, 1145–1147 (2006).
L. Antonucci, et al., “14 fs high temporal quality injector for ultra-high intensity laser,” Opt. Commun. 282, 1374–1379 (2009).
5.  M. P. Kalashnikov et al., “Suppression of gain narrowing in multi-TW lasers with negatively and positively chirped pulse amplification,” Appl. Phys. B 81, 1059 (2005).
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6. Spatio-Temporal Chirped Pulse Amplification
(STCPA) (1/2)
Principle :
Combination of temporal and spatial dispersion enable amplified spectra to be unaffected by saturation effect.
i.e. spatially spreading spectral components to separately amplify them and thus deleting the gain competition
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7. Spatio-Temporal Chirped Pulse Amplification
(STCPA) (1/2)
Principle :
Combination of temporal and spatial dispersion enable amplified spectra to be unaffected by saturation effect.
Oscillator
Stretcher
Power amplifier
Compressor
Classical CPA scheme
Ti:Sa Crystal
Pump Beam
IR Beam
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8. Spatio-Temporal Chirped Pulse Amplification
(STCPA) (1/2)
Principle :
Combination of temporal and spatial dispersion enable amplified spectra to be unaffected by saturation effect.
Ti:Sa Crystal
Pump Beam
IR Beam
STCPA scheme
Spatial spreading
Spatial compression
Oscillator
Stretcher
Power amplifier
Compressor
Gain zone shape adaptation
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9. Spatio-Temporal Chirped Pulse Amplification
(STCPA) (2/2)
Advantages :
No spectral shifting while preserving energy extraction in saturation regime i.e. saturation effect is equally distributed on all the spectral range instead of only the infrared edge.
Conditions :
Input pulse has to be collimated
Spatial spreading law has to be inverse of that of spatial compression
Pump beam has to be matched to the oblong seeded beam
Inconvenient :
Gain narrowing not avoided in this configuration
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10. Experiment Set Up Frequency doubled Nd:YVO4 3,7 W Ti:Sa Oscillator
3,8 nJ / 80 MHz
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11. Öffner triplet Stretcher
Experiment Set Up
Frequency doubled
Nd:YVO4
3,7 W
Öffner triplet Stretcher
Ti:Sa Oscillator
250 ps
3,8 nJ / 80 MHz
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12. Regenerative Amplifier Öffner triplet Stretcher
Experiment Set Up
Frequency doubled
Nd:YVO4
1,5 mJ
1 kHz
3,7 W
Regenerative Amplifier
Öffner triplet Stretcher
Ti:Sa Oscillator
7,1 mJ / 1 kHz
250 ps
3,8 nJ / 80 MHz
Q-switched Nd:YLF
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13. Regenerative Amplifier Öffner triplet Stretcher
Experiment Set Up
Frequency doubled
Nd:YVO4
500 µJ
1 kHz
+ Birefringent Plate
3,7 W
Regenerative Amplifier
Öffner triplet Stretcher
Ti:Sa Oscillator
7,1 mJ / 1 kHz
250 ps
3,8 nJ / 80 MHz
Q-switched Nd:YLF
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14. Regenerative Amplifier Öffner triplet Stretcher
Experiment Set Up
Cylindric lenses
180 mJ / 10 Hz
Nd:YAG
LaK8
Prisms
Multipass amplifier
6 passes
Ti:Sa Absorption : 90%
Output
Ø = 15 mm
40 µJ
10 Hz
Frequency doubled
Nd:YVO4
Pockels Cell
500 µJ
1 kHz
+ Birefringent Plate
3,7 W
Regenerative Amplifier
Öffner triplet Stretcher
Ti:Sa Oscillator
7,1 mJ / 1 kHz
250 ps
3,8 nJ / 80 MHz
Q-switched Nd:YLF
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15. Experiment Set Up Cylindric lenses 180 mJ / 10 Hz Nd:YAG LaK8 Prisms
Multipass amplifier
6 passes
Ti:Sa Absorption : 90%
Output
Ø = 15 mm
40 µJ
10 Hz
IR Beam Before Prisms
IR Beam After Prisms
Øy,FWHM = 1900 µm
Øx,FWHM = 3000 µm
Øx,y,FWHM = 1900 µm
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Aspect Ratio of 1,6

16. Experiment Set Up Cylindric lenses 180 mJ / 10 Hz Nd:YAG LaK8
Prisms
Multipass amplifier
6 passes
Ti:Sa Absorption : 90%
Output
Ø = 15 mm
40 µJ
10 Hz
IR Beam After Prisms
Wavelength spreading
19 nm/mm
Øy,FWHM = 1900 µm
Øx,FWHM = 3000 µm
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17. Experiment Set Up Cylindric lenses 180 mJ / 10 Hz Nd:YAG LaK8 Prisms
Multipass amplifier
6 passes
Ti:Sa Absorption : 90%
Output
Ø = 15 mm
40 µJ
10 Hz
Left Side
Øy,FWHM = 600 µm
Øx,FWHM = 4000 µm
Output Beam Pump
Øx,y,FWHM = 10 mm
Right Side
Øy,FWHM = 600 µm
Øx,FWHM = 4000 µm
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18. Experiment Set Up Output 28 mJ ~ 1,8 J/cm² Cylindric lenses
180 mJ / 10 Hz
Nd:YAG
LaK8
Prisms
Multipass amplifier
6 passes
Output
28 mJ
~ 1,8 J/cm²
Ti:Sa Absorption : 90%
Ø = 15 mm
40 µJ
10 Hz
FFT Calculation
Simulation
CPA
Experiment STCPA
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19. No angular and transverse chirp
Experiment Set Up
Cylindric lenses
180 mJ / 10 Hz
Nd:YAG
LaK8
Prisms
Multipass amplifier
6 passes
Output
28 mJ
~ 1,8 J/cm²
Ti:Sa Absorption : 90%
Ø = 15 mm
40 µJ
10 Hz
Far field
Near field
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No angular and transverse chirp

20. Conclusion
First amplification scheme in Ti:Sa using a combination of spatial and temporal chirp
STCPA concept avoids effects of saturation / enables a control of the amplified spectrum at high energy
Using appropriate chirp tool : output beam free of angular and transverse chirp
Fully relevant technique for obtaining very intense and short laser pulses (energy in excess of 10’s of Joules) with good temporal quality
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21. Thank you !
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