CTF3 photo injector laser status

1. CTF3 photo injector laserstatus CERN 17 July 2009 CLIC meeting

2. Laser Chain Micro pulses at 1.5 GHz ~666ps ~8ps 400ms Seed beam: 1.5GHz repetition rate (~666ps) ; 10 W avg power 7 nJ energy 2 Nd:Ylf multi passages amplification stages: (1-50)Hz Gating system: 1ns -> 10ms Harmonics: SHG+FHG IR ->Green->UV Electron Gun CALIFES / PHIN

3. AMP2 2-pass Nd:YLF amplifier Nd:Ylf rod 1cm diameter; 12 cm length From AMP1 83cm 80cm M1 Nd:Ylf rod M2 Faraday rotator out f1=+206 mm f1= + 458mm isolator l/2 36cm f2= -206mm 2nd pass out 395 mm 400 mm 1st pass • ~8.5KW peak power • (pumping diodes @90amps) • ~6mJ micro pulse energy • (4mJ old value)

4. In theory... M. Petrarca CERN et M. Martyano Institute of Applied Physics, Nizhny Novgorod, Russia, work in progress Considering G0=863 Output power [KW] Input power [KW] fig. 2 • It is extremely important: • to reduce losses in between AMP1 and AMP2 (Pin ~ 1.5KW now) • to fill up all the rod

5. Transverse beam profile: 1st passage amplification ……non satisfactory matching ……beam transverse profile must be studied form the beginning of the laser chain ……elliptical shape must be converted in circular one

6. Harmonic Conversion (overcoming pulse pickers ) FHG now!: For 500 ns macro pulse duration; rms UV energy fluctuaction (1-2)%: KDP 7.5 mm: Eg=1.45mJ EUV =0.44mJ  ~580nJ micro bunch KDP 10 mm: Eg=1.45mJ EUV =0.54mJ BBO 11 mm: Eg=1.45mJ EUV =0.47mJ ADP 20 mm: Eg=1.49mJ EUV =0.61mJ ADP 7.5 mm: Eg=1.45mJ EUV =0.60mJ  ~800nJ micro bunch For 1300ns macro pulse duration rms UV energy fluctuations (1-2)% : ADP 15 mm: Eg=3.6mJ EUV =1.3mJ  ~666nJ micro bunch ADP 20 mm: Eg=3.6mJ EUV =1.29mJ PHIN Considering the losses (10% beam line + 8% window + 20% metallic mirror =38%) The ~360nJ energy required is now available from the laser Note that with ~340nJ on laser table = ~235nJ estimated on cathode we obtain ~1.6nC stable charge (and 2.3 nC with a new cathode)

7. CALIFESPulse picker Pulse pickers + wave plate and polarizer 8.7mJ 5.6mJ T=64% • Pulse Picker system  loss = > Transmittivity ~64% • Total losses CALIFES transport line: 43% (transport ~21% + Coupling ~22%) •  Now! UV energy KDP(15mm) ~500nJ on laser table  290nJ on cathode (~200 Before) •  Available! UV energy KDP(20mm) ~640nJ on laser table  364nJ on cathode

8. Phase Coding 140ns 666ps 666ps 666ps 666ps 666ps 666ps 666ps 666ps 666ps 666ps 666ps 666ps 666ps 666ps 666ps 333ps 666ps 666ps 333ps 333ps 999ps 999ps 333ps 666ps 666ps Phase Codinginvestigation and prospective Phase coding has been tested at the university of Milan on a different laser. It has been shown that it introduces too high losses (300mW-> ~7mW) but the output time structure is satisfactory Proposal; 1) Take the phase coding system back @ CERN as soon as possible. 2) Repeat the test which has been done in Milan: control the generated time structure and power losses on our laser system 3) Investigate possible new hardware with better performances 4) Study the possibility to have a more compact fiber system (osc+phase coding + preamplifier)

9. Manpower -> Marta Divall is going to join the laser group + Stable Laser -> The laser is now working in stable condition = Dedicated time for phase coding development on site. Time schedule -> dedicated “laser time” is required If the phase coding system will introduce such high losses also in this laser system, a booster amplifier must be bought. An estimation for a fiber amplifier from Keopsys is ~43KEuro (10W output) The major problem is that Keopsys, like other companies don’t have a seed with the same characteristics we have so all what they can guarantee must then be tested on site on the real laser. We are investigating about some technical details with Keopsys. If their amplifier will be feasible then the laser scheme will be slightly simplify since we will not need the preamplifier. If fiber amplifier will not be a feasible solution then a conventional amplifier similar to the preamplifier we are using will be required.

10. Conclusions and prospective • 1) The second amplifier configuration has been modified: • 2 collinear passages Now! • 2 cross passages Before! • losses are reduced, final peak power ~8.5KW, ~6mJ in micro pulse [~4mJ before] • Future improvement: • 1) Investigation of the beam profile changes through all the laser chain. • 2) better matching of the beam profileand intensity distribution into the amplifier • (re-design of beam line) • 3) different principles of operation (seeding of the already pumped amplifier)… • 2) Different harmonic generation crystals tried: • ADP, KDP - look promising : • high efficiency, satisfactory transverse beam quality • BBO – lowest conversion efficiency and bad transverse beam quality due to walk off • Further studies on harmonic conversion: temperature stabilization, longer KDP crystals; DKDP in non-critical phase matching • 3) Phase coding analysis on the “real” low power laser part must be done to get all the required information about the implementation of the device in the whole laser chain. • Laser group is growing: Marta Dival will join us from September-> dedicated time on the phase coding is under organization. • Priority: measure the performance of the phase coding on this laser. Laser time is required