1. history, status and upgrade
Photo-injector laser
history, status and upgrade
Massimo Petrarca

2. Laser overview 1.5 GHz Nd:YLF Oscillator + Preamplifier 1047nm
Micro pulses at 1.5 GHz
~666ps; 10W;~8psFWHM
3-pass Nd:YLF
Amplifier; 5-50 Hz
2 pass Nd:YLF
Amplifier
5-50Hz
Drive Beam (PHIN); Probe beam
~600ps=<Dt=<DtPC UV Dt Dt
Green Dt IR
Optical gate
(Pockels cell) PC 4
BBO 2
KTP
Pulse
picker

3. … Events Chronology January 08…. Major issues
Amp2 Problems (energy)
Synch. Problem (to 1.5 GHz clock)
January 08…. Major issues
Harmonic Generation Scheme
Beam line down to the Gun
Amplifier drivers
Harmonic Conversion
Efficiency & Stability
studies
Jan ->May 08…. Just Amp1
New problems:
Amp1
June-July 08…
Amp1 investigation:
pulse train instabilities (ASE, parasitic lasing) …

4. Beam size almost constant throughout all the passages
Summer 08…
Amp1 investigation:
pulse train instabilities (ASE, parasitic lasing)
Amp1 has been modified according to 3 different scheme:
Small beam size in 1st passage while it grows in the 2nd and 3rd filling up even more the rod
Beam size that fills the rod in the 1st passage while in the 3rd it is small
Beam size almost constant throughout all the passages

5. . August 08… Power Measurements Amp1: Unamplified  ~ 5.6 W @ 80a
1st pass
2nd pass
3rd pass
F1 = +1146mm
Preamp. beam
58cm
54cm
21cm
3.5cm
2.5cm
5cm
Power Measurements Amp1:
Unamplified  ~ 5.6 W
@ 50 amps  ~ 6.7 W
@ 60 amps  ~ 7.4 W
@ 70 amps  ~ 8.1 W
@ 80 amps  ~ 8.8 W
@ 90 amps  ~ 9.7 W  ~3.0 KW
@ 80a
Rod image
X=5.04 mm
Y=4.72 mm
-Final configuration: 3passages trough the rod with F1 to ~ compensate
for the beam divergence: X(3rd pass)-X(1st pass)~1.2mm; Y(3rd pass)-Y(1st pass)~1mm .
Nominal power ~3KW reached
Satisfactory trace pulse stability achieved .
August 08…
Amp1 problems have been solved:
Second check: Harmonic Generation

6. Laser overview 1.5 GHz Nd:YLF Oscillator + Preamplifier 1047nm
Micro pulses at 1.5 GHz
~666ps; 10W;~8psFWHM
3-pass Nd:YLF
amplifier
2 pass Nd:YLF
amplifier
Drive Beam (PHIN); Probe beam
~600ps=<Dt=<DtPC UV Dt Dt
Green Dt IR
Optical gate
(Pockels cell) PC 4 2
Pulse
picker

7. IR energy within 2ms gate GREEN energy within 2ms gate
Harmonic Conversion
Efficiency & Stability
studies
August/Sept 08…. Just Amp1
IR energy within 2ms gate
GREEN energy within 2ms gate UV
Energy within
2ms gate
PC on 2ms
( Best Result )
( )mJ
std=0.02mJ
1.170 mJ
Std=0.16mJ
~44 % efficiency
0.398 mJ Std=0.012
~34 % efficiency
133.3 nJ in a micro pulse
NO problems at all :
confirmation Amp1 prob. have been solved !!!
Harmonic Conversion
Efficiency & Stability
studies
August/Sept 08…. Just Amp1 .

8. September 08…. Status: .
Amp driver (1 month investigation & company visit) .
Harmonic Generation Scheme
with Amp1 .
Beam line down to the Gun
In collaboration with Guy Cheymol “CEA Saclay”
Synch. Problems (Laser -> Gun)
Had to be resolved before Amp2 investigations:
due to achieved UV energy (~130nJ)
it was worthwhile to try e- generation with just Amp1
Amp2 Problems (for energy)

9. . Jreal ~ 634 fs rms jitter required <1ps
Synch. Problems (Laser -> Gun)
HighQ expert came:
settings of the oscillator end-cavity mirror restored
(semiconductor saturable absorber mirror “SESAM”):
50C Degree
Problem has been resolved
After on site investigation,
oscillator cavity perturbations due to thermal effects were suspected
Lecroy SDA (16GHz, 60GS/s+ NewFocus Photodetector25GHz)
JNF: jitter noise floor ~ 350 fs
Jmeas: 724fs
Jreal ~ 634 fs
rms jitter required <1ps
Synch. Problems (Laser -> Gun) .

10. Amp2 changes & results September / October 08 M12 M11 1st pass
2nd pass
F2 = +300mm M6
Nd:Ylf rod
Periscope + Farady
F3 = -114mm
Amp1 3rd pass. M7 M8 M9
M10
94cm
57.5cm
20.5cm
122cm
2.5cm
29.5cm
22cm
75cm
156cm
Tot:48cm
Pockels
Cell
20cm
25cm
26cm
7cm
F4 = +802mm
F5 = +402mm
14.5cm
-Present configuration:
2passages trough the rod with F3 and F2 for the matching: “beam size rod size”
Satisfactory trace pulse stability has been achieved
Uncoupling system between Amp1 & Amp2 “Periscope + Faraday isolator” installed

11. Laser overview 1.5 GHz Nd:YLF Oscillator + Preamplifier 1047nm
Micro pulses at 1.5 GHz
~666ps; 10W;~8psFWHM
3-pass Nd:YLF
amplifier
2 pass Nd:YLF
amplifier
Drive Beam (PHIN); Probe beam
~600ps=<Dt=<DtPC UV Dt Dt
Green Dt IR
Optical gate
(Pockels cell) PC 4 2
Pulse
picker

12. Power Measurements Amp1 @90A
Amp2 changes & results
Power Measurements
+Amp2 ..:
@ 50 amps  ~ 10.0W
@ 60 amps  ~ W
@ 70 amps  ~ 11.2 W
@ 80 amps  ~ 11.6 W
@ 90 amps  ~ 12.3 W  ~6.3 KW
Final check:
Harmonic generation

13. Achieved UV energy 234nJ with 2%=<jitter<3% during run
Harmonic Conversion
Efficiency & Stability
studies
Amp1+Amp2
=>Satisfactory
Sept/Oct 08…. Just Amp1 IR
energy within 2ms gate
GREEN UV
Energy within
2ms gate
PC on 2ms
( )mJ
std=0.26mJ
3.23 mJ
Std=0.07mJ
40% efficiency
0.692 mJ
Std=0.024
~234 nJ in a micro pulse
22% efficiency
Achieved UV energy 234nJ with 2%=<jitter<3% during run
Expected UV energy ~370 nJ
Obtained results can be improved….

14. Dt Dt Dt Optical gate (Pockels cell) PC 2 Pulse picker
Drive Beam (PHIN); Probe beam
~600ps=<Dt=<DtPC UV Dt Dt
Green UV Dt
Optical gate
(Pockels cell) PC 4 2
Pulse
picker

15. . . . Summary: …. Beam line down to the Gun
Synch. Problems (Laser -> Gun) .
Harmonic Generation Scheme
GREEN UV
~44 % eff
133.3 nJ
~34 % eff
40% eff
~234 nJ
22% eff
But it can be improved with both Amp working:
Better determination of the beam size and properties onto the crystals,
Institute Applied Physics ( IAP, Russia) collaboration proposal
(KDP instead of BBO, beam profile)
With the above laser characteristics
We have been able to run both the two photo injector lines
PHIN & CALIFES
See talks: R. Losito O. Mete, S. Doebert,
W. Farabolini ….

16. Laser is now working again….
Amp2 energy ~7KW (about half of the design project )
It can be improved:
Add 3rd passage & matching beam size rod.
IAP (Russia) collaboration proposal:
layout modification, input profile modification…
Remark:
Unfortunately the oscillator broke the last week of CALIFES run…..the investigation and reparation took 2.5week.
Laser is now working again
!!!!
A solution has to be seek out not to be cast out for such a long time :
Spares...a hole system? Just drivers & diodes ? Insurance agreement with the company for a faster help ?

17. Upgrade the laser Second Amp:
It has to be studied and characterize to improve its performances and push it to its limit!
Time and manpower help is needed on site!!
Institute Applied Physics (Russia) collaboration:
Proposing interesting changes in the Amp set up but the improvement is not guarantee; nevertheless it is worthwhile to try.
The possibility to buy a second oscillator
as a test bench for Phase coding & as spare part has to be studied as well as a new scheme to substitute the fiber phase coding.

18. The end Special thanks:
Marta Divall & C. Vicario: laser chain main modification
Guy Cheymol: beamline, harmonic generation
V. Fedosseev: laser
E. Chevallay, K. Elsener ,N. Lebas, A. Masi and all his crew: electronic, technical etc…support
R. Losito
The end

19. Not acceptable for the laser system
Phase Coding Phase Coding University of Milan With 100MHz lser beam
Power test of full system: Pin = 300 mW Pout = 2 mW measured
Not acceptable for the laser system
S. Cialdi, I. Boscolo University of Milan

20. Phase Coding With 100MHz laser beam Modulator performances S. Cialdi,
I. Boscolo University of Milan