1. Workshop for advanced THz and Compton X-ray generation
Report on Ti:Sa Laser system for LUCX RF gun
K. Lekomtsev on behalf of FSTB collaboration

2. Outline General layout of the fs laser. Oscillator. Stretcher.
Regenerative amplifier and multi – pass amplifier.
Compressor.
Longitudinal diagnostics (Bonsai).
Integration of Ti:Sa laser system into LUCX infrustructure.
Third harmonic generation.
Pulse splitting scheme.
Autocorrelation technique for intra-train measurements.
Weekly LUCX meeting

3. General layout Longitudinal diagnostics Compressor Multi-pass
amplifier
Stretcher
RGA
Oscillator
Weekly LUCX meeting

4. Performance Performance Measured Specified Repetition rate 10 Hz
Central wavelength
805 nm
795 – 815 nm
Pulse energy before compression
22 mJ
> 20 mJ
Pulse energy after compression
16 mJ
> 12 mJ
Pulse duration
without dazzler:
with dazzler:
39 fs
35 fs
< 40 fs
< 35 fs
Energy stability 22 mJ at 800 nm
1.4 %
< 2 %
Contrast ns
1x 10 −3.47
< 1x 10 −3
Weekly LUCX meeting

5. Oscillator
beam
blocker M2
Ti:Sa M1
532 nm M6 M5 M7
800 nm OC
M4 – mode-locking mirror M4 M3
The pump laser (CW diode – pumped solid state laser) seeds the oscillator with 532 nm light.
The output beam of the pump laser is S polarised.
Compensation plate (CP) directs the beam after the output coupler (OC) and adjusts
the dispersion for short pulses.
Extra – cavity dispersion compensation (ECDC) controls the dispersion of the OC and CP
to get the shortest pulse.
Weekly LUCX meeting

6. Oscillator Oscillator type Synergy Pro Rep. rate 71.4 MHz Cooling
temp.
19 ℃
Mode lock
power
485 mW
Pump laser
3.6 W
Spectrum
width
110 nm
Central
wavelength
797 nm
Pulse
length (spec)
~10 fs
energy
~ 6.8 nJ
Weekly LUCX meeting

7. Stretcher Parameter Value Input power 430mW Output 150mW Transmission
35 %
Pulse
duration
~ 1 ps
8 passes on the stretcher
grating with the reference
to the input beam:
Weekly LUCX meeting

8. RGA and multi-pass amplifier
Weekly LUCX meeting

9. RGA and multi-pass amplifier
Seeded RGA spectrum (30 nm FWHM)
Pockels Cell 1 Trig
Photo diode 1
free running build up time
Beam profile at the output of the multi-pass amplifier
FWHM ~ 2.5 mm
Pockels Cell 1 Trig
Photo diode 1
seeded build up time
Weekly LUCX meeting

10. RGA and multi-pass amplifier
RGA output beam profile
Weekly LUCX meeting

11. Compressor
30 nm FWHM
Compressor compensates for the group delay dispersion introduced
by the stretcher and the amplifiers.
Compressor efficiency – 75 %
16 mJ at 39 fs pulse length yields
410 GW peak power
Weekly LUCX meeting

12. Compressor
Compressor output beam profile
Weekly LUCX meeting

13. Longitudinal diagnostics (Bonsai)
Parameter
Value
Spectral
range
720–880 nm
Temporal fs
Input
polarisation P
Pulse
energy
required
> 0.8 nJ at 70 MHz rep.
>1𝞵J at
1-10 Hz rep.
Crystal
0.3 mm KDP
KDP
(Potassium Dihydrogen Phosphate)
Weekly LUCX meeting

14. Longitudinal diagnostics (Bonsai)
Cross size of SH beam:
𝐷 𝑧 = 𝑡𝑐 𝑠𝑖𝑛 𝜑 2
𝑡 – pulse duration, 𝜑 – the angle between
the combined beams in the crystal, c – light
velocity of the base frequency in the crystal.
Time delay ∆𝑡 causes the SH cross distribution
to shift by an amount of 𝑍 0 :
𝑍 0 = ∆𝑡𝑐 2𝑠𝑖𝑛 𝜑 2
From the above expressions the pulse duration:
𝑡= 𝐷 𝑧 ∆𝑡 𝑍 0
Weekly LUCX meeting

15. Longitudinal diagnostics (Bonsai)
Weekly LUCX meeting

16. Nd:YAG laser system
Weekly LUCX meeting

17. FSTB - LUCX integration
LUCX beam line
FSTB
LUCX
Nd:YAG
Weekly LUCX meeting

18. Laser Transport Line construction
LUCX beam line
Weekly LUCX meeting

19. THG kit
Weekly LUCX meeting

20. Pulse splitter GVD plate might be cut in a wrong way
Weekly LUCX meeting

21. Pulse splitter (transverse profile)
GVD plate might
be cut in a wrong way
Weekly LUCX meeting

22. Pulse splitter (transverse profile)
Fixed arm:
Adjustable arm:
GVD plate might
be cut in a wrong way
Weekly LUCX meeting

23. Pulse splitter (Bonsai)
Adjustable arm:
Bonsai was used to measure
consecutive pulses coming
from the fixed and adjustable
arms of the pulse splitter.
Fixed arm:
Weekly LUCX meeting

24. Visible single-shot autocorrelator based on the two-photon fluorescence.
Y.M. Li and R. Fedsojevs,
APPLIED OPTICS, 15, N15, 1996.
GVD plate might
be cut in a wrong way
The time resolution is limited only by the imaging system for given crystal properties.
Weekly LUCX meeting

25. Plans and outlook. Successful strat-up of the laser system.
Necessary infrastructure almost completed.
Third harmonic generation (april 2013).
Laser transport line completion (april – may 2013).
Pulse splitting scheme (summer 2013).
Pointing stability, long term power stability, laser diagnostics, micro-bunch beam generation, laser beam focusing.
GVD plate might
be cut in a wrong way
Weekly LUCX meeting