CTF 3 lasers Marta Csatari Divall Eric Chevallay

CTF 3 lasers Marta Csatari Divall Eric Chevallay, Valentine Fedosseev, Nathalie Lebas, Roberto Losito, Massimo Petrarca, CERN, EN-STI CTF 3 Collaboration meeting 6 th May 2010

Outline • Photo-injectors for CTF 3 • Current laser setup • Results on PHIN • Feedback stabilization • Phase coding • Laser for CLIC • Future plans Marta Csatari Divall CTF 3 Collaboration meeting 6 th May 2010 Photo-injector laser for CTF 3

Photo-injectors for CTF 3 Drive Beam Injector thermionic gun Possible change over in next few years Delay Loop: 2 Combiner Ring: x 4 Drive Beam Accelerator PHIN CLEX 2 beams test area CALIFES Probe beam photo-injector Electrons PHIN Drive beam photo-injector test stand UV laser beam Marta Csatari Divall CTF 3 Collaboration meeting 6 th May 2010 http: //clic-study. web. cern. ch/clic-study/ charge/bunch (n. C) gate (ns) bunch spacing(ns) bunch length (ps) Rf reprate (GHz) number of bunches machine reprate (Hz) margine for the laser charge stability QE(%) of Cs 2 Te cathode DRIVE beam PROBE beam PHIN CALIFES 2. 3 0. 6 1200 19. 2 0. 666 10 10 1. 5 1802 32 5 5 1. 5 <0. 25% <3% 3 0. 3 Machine parameters set the requirement for the laser Photo-injector laser for CTF 3

Laser requirements Laser in IR Laser in UV PARAMETERS PHIN laser wavelegth (nm) energy/micropulse on cathode (n. J) energy/micropulse laserroom (n. J) energy/macrop. laserroom (u. J) mean power (k. W) average power at cathode wavelength(W) micro/macropulse stability conversion efficiency energy/macropulse in IR (m. J) energy/micropulse in IR (u. J) mean power in IR (k. W) average power on second harmonic (W) average power in final amplifier (W) CALIFES 262 >363 544 9. 8 E+02 0. 8 262 947 1420 4. 1 E+01 2. 1 0. 005 <0. 25% 0. 1 9. 8 5. 4 8. 2 0. 49 9 2. E-04 <3% 0. 15 0. 3 9. 5 14. 2 1. E-03 15 Achieved Not available yet The laser was not designed for CALIFES parameters Feedback stab. Phasecoding test 1. 5 GHz Synched oscillator Cw preamplifier 10 W 3 -pass amplifier 3. 5 k. W 2 -pass amplifier 8. 3 k. W 7. 8 k. W 14. 8 m. J in 1. 2μs 2ω 3. 6 k. W 4. 67 m. J in 1. 2μs 4ω 1. 25 k. W 1. 5 m. J in 1. 2μs Feedback stab. Marta Csatari Divall CTF 3 Collaboration meeting 6 th May 2010 Photo-injector laser for CTF 3

Outline • Photo-injectors for CTF 3 • Current laser setup • Results on PHIN • Feedback stabilization • Phase coding • Laser for CLIC • Future plans Marta Csatari Divall CTF 3 Collaboration meeting 6 th May 2010 Photo-injector laser for CTF 3

Contributions Harmonics Phase-coding test Phasecoding test 1. 5 GHz Synched oscillator Cw preamplifier 10 W Cooling 3 -pass amplifier 3. 5 k. W 2 -pass amplifier 8. 3 k. W 7. 8 k. W 14. 8 m. J in 1. 2μs 2ω 3. 6 k. W 4. 67 m. J in 1. 2μs 4ω 1. 25 k. W 1. 5 m. J in 1. 2μs AMP 1 head assembly High. Q front end AMP 1 and AMP 2 Marta Csatari Divall Photonics Europe April 14, 2010 Stability of a high power diode-pumped Nd: YLF laser system for photo-injector applications at CERN

Amplifiers NE W AMP 1 AMP 2 Pumping power 15. 5 k. W 18. 8 k. W Rod length x diameter 8 cm x 0. 7 cm (7 cm pumped) 12 cm x 1 cm (11 cm pumped) Number of passes 3 non-collinear 2 collinear Small signal gain coeff. (1/cm) 1. 162 0. 253 Steady-state gain 580 4. 1 Power output 3. 2 k. W 8. 3 k. W Extractable from pump 53% 49% Marta Csatari Divall CTF 3 Collaboration meeting 6 th May 2010 ! Photo-injector laser for CTF 3

Harmonic stages 1047 nm 523 nm 262 nm RMS stab. (train) 0. 23% 0. 8% (0. 45%) 1. 3% (1. 6%) Energy/pulse (μJ) 5. 37 2. 5 0. 87 Pulse length (ps) 7 7 ~5 ps Beamsize (μm. Xμm) 418 X 372 370 X 224 Conversion efficiency (T=89% to harmonics) 47% (best 50%) 35% (best 47%) Crystal - KTP 11 mm ADP 20 mm @23. 60 C Preliminary measurement on response to long train 1. 2 μs Amp 2 as in table Amp 1 only X 4 less intensity Marta Csatari Divall CTF 3 Collaboration meeting 6 th May 2010 • 1 cm KDP • 18% efficiency • Flat response • Beam size/ shape to be optimized Photo-injector laser for CTF 3

Outline • Photo-injectors for CTF 3 • Current laser setup • Phase coding • Diagnostics/Results on PHIN • Feedback stabilization • Laser for CLIC Marta Csatari Divall CTF 3 Collaboration meeting 6 th May 2010 Photo-injector laser for CTF 3

Laser diagnostics CALIFES PHIN ~70 m 64% to cathode under vacuum Beam transport am radius (mm) ~11 m 71% to cathode Distance from 4 th harmonic crystal (mm) Marta Csatari Divall CTF 3 Collaboration meeting 6 th May 2010 • Transmission is low for CALIFES line • Pointing instabilities are high due to long distances • Closer to the gun would be better • Automated measurement system needed Photo-injector laser for CTF 3

Current status on PHIN pointing Laser position/size worst best Size (mm) Taken with virtual cathode camera and OTR screen camera Electron beam position/size Movement (mm) Size (mm) Movement (mm) x y δx δy 0. 74 0. 64 0. 15 20% 0. 13 20% 1. 46 1. 76 0. 6 41% 0. 65 37% 0. 71 0. 67 0. 24 34% 0. 27 40% 1. 55 2. 86 0. 71 46% 0. 67 23% Marta Csatari Divall CTF 3 Collaboration meeting 6 th May 2010 Photo-injector laser for CTF 3

Current status on PHIN amplitude In laser room Measured (no sat. exp. ) 0. 23% In PHIN Green 0. 8% (0. 45%) UV 1. 3% (1. 6%) best IR worst Macropulse stability Amplitude stability Train length Laser energy (n. J) Current/ bunch (n. C) (ns) 369 1. 3% RMS 1. 5 0. 8% RMS 1250 330 2. 6% 1 2. 4% 1300 Thanks to PHIN team Current: sigma =0. 8 % Marta Csatari Divall CTF 3 Collaboration meeting 6 th May 2010 • Exceptional stability without feedback stabilization! • Pointing instabilities can be improved by better airflow control • Amplitude feedback system is necessary Photo-injector laser for CTF 3

Outline • Photo-injectors for CTF 3 • Current laser setup • Results on PHIN • Feedback stabilization • Phase coding • Laser for CLIC • Future plans Marta Csatari Divall CTF 3 Collaboration meeting 6 th May 2010 Photo-injector laser for CTF 3

Sources of instabilities Amplitude Pointing • Electrical noise/power supplier noise • Water cooling system • Pumping diodes • Seed source (osc+preamp) • Phase coding • Pointing (amplification + harmonic stages) • Air conditioning (temperature variation+ airflow) • Vibration • Airflow in beam transport • Lack of relay imaging • Thermal drifts • Mechanical vibration • Some also affecting the measurement system! Marta Csatari Divall CTF 3 Collaboration meeting 6 th May 2010 Photo-injector laser for CTF 3

Sources of instabilities Mirror inside the gun Improving the environment for the laser is necessary: • Better temperature stabilization • Less airflow, better enclosure (planned for May 2010) • Move the laser closer to the gun • Change to solid metal mirror Marta Csatari Divall CTF 3 Collaboration meeting 6 th May 2010 UV train RMS energy amplitude Reflectivity (m. J) stability 0. 264 4. 56% 69% 1: on small crack 0. 334 2. 69% 87. 4% 2: on reflective surface 0. 167 10. 26% 43. 7% 3: on big crack Photo-injector laser for CTF 3

Scheme to improve stability • Similar system tested at RAL with 4 μs speed → 0. 25%RMS over 140 μs in the UV • Commercial LASS-II by Conoptics at green wavelength 1/1@ 500 k. Hz (Int. Ref. Mode) 5/1 @ 100 k. Hz 18/1 @50 k. Hz 100/1 @10 k. Hz Noise measured on PILOT system 200/1 @1 k. Hz 250/1 @200 hz Could be reversed for feed forward option In TESLA this system was invented by I. Will and his group 0. 7% rms stability was achieved from 3% with 70% transmission Custom design for quasi-cw available • EO modulators ordered for in house tests • System specifications by spring 2011 HOW to measure? • Development of a measurement system with >104 dynamic range is necessary • Challenging task with the phase-coded short train • More detailed fast noise measurements planned for 2010 Marta Csatari Divall CTF 3 Collaboration meeting 6 th May 2010 Photo-injector laser for CTF 3

Outline • Photo-injectors for CTF 3 • Current laser setup • Results on PHIN • Feedback stabilization • Phase coding • Laser for CLIC • Future plans Marta Csatari Divall CTF 3 Collaboration meeting 6 th May 2010 Photo-injector laser for CTF 3

Phase-coding üSlow switching demonstrated üRecombination and delay measured • Damage due to the high input power, only 10 m. W output • RF driver is not up to our specification(see picture) NEW scheme Losses in % waveplate 20% Oscillator 320 m. W 82% 11% 2% Fiber splitter coupler Alternative scheme Losses in % waveplate 2% Full power train from 2% Lens system amplifiers Marta Csatari Divall CTF 3 Collaboration meeting 6 th May 2010 20% 333 ps delay EO modulator T=9% Variable attenuator EO modulator 2% 2% Polarizer Booster amplifier 300 m. W Fiber outcoupler 11% 20% 82% 5% Driver response to square input (voltage applied to modulator) 2% 55% waveplate T=38% Pockels cell Polarizer With type 2 crystal we could get T=80% • Components in purchasing • Booster amplifier ordered in Feb/2010 • Planned commissioning on PHIN autumn/2010 • Driver specification is very demanding (3. 6 MHz, fast rise time , high average power) • Monitor latest status for available drivers on the market Photo-injector laser for CTF 3

Laser driven photo-injector option ADVANTAGES To demonstrate Proven capability to synchronize to external RF source Amplitude stability <0. 25% RMS for PHIN <0. 1% RMS for CLIC Flexibility for timing structure, single pulse operation Working phase-coding system Size, shape, pulselength, energy can be optimized for machine Reliable long term operation (~1000 hour running time during 2009 is already good) Can produce polarized electrons High charge Gives smaller transverse emittance No energy tails (from the laser) No satellites Marta Csatari Divall CTF 3 Collaboration meeting 6 th May 2010 Photo-injector laser for CTF 3

Outline • Photo-injectors for CTF 3 • Current laser setup • Results on PHIN • Phase coding • Feedback stabilization • Lasers for CLIC • Future plans Marta Csatari Divall CTF 3 Collaboration meeting 6 th May 2010 Photo-injector laser for CTF 3

Lasers for CLIC Marta Csatari Divall CTF 3 Collaboration meeting 6 th May 2010 Photo-injector laser for CTF 3

Main challenges identified • Lack of laser time for research development on the laser • Long train operation for CLIC (140 μs) • High average power operation (100 Hz) • Stability and stabilization • (Phase coding on the way independently from operation until installation on PHIN ~October 2010) Marta Csatari Divall CTF 3 Collaboration meeting 6 th May 2010 Photo-injector laser for CTF 3

Modifications to the setup • Using ‘leakage’ wherever we can • No interruption to operation • High repetition rate test are risky and still cannot be performed Marta Csatari Divall CTF 3 Collaboration meeting 6 th May 2010 Photo-injector laser for CTF 3

Independent laser system for CALIFES • • Laser design was for long trains of the CLIC drive beam CALIFES requires only up to 226 pulses (160 ns) 1μJ in the UV is necessary for short train, which have not been delivered yet CALIFES will be used as a diagnostic test bench until 2015 at least PILOT laser tested on CTF 2 This is how long the CALIFES train is Allow the amplifier to store the energy before pulses arrive Higher energy can be reached Stability needs to be investigated For <1% change at the output the switch on time has to be <350 ns accurate <1% variation over the train at nominal energy Marta Csatari Divall CTF 3 Collaboration meeting 6 th May 2010 • ~60 k. Euro for replacing old parts • The footprint is 60 cm X 150 cm + the oscillator • Deliverable by Spring 2011 • In collaboration with IAP for amplification • Rest of the system needs new oscillator Photo-injector laser for CTF 3

New source for PHIN laser and CLIC • • • 500 MHz front end and the existing amplifiers could be used for tests for CLIC With reprate tripling configuration PHIN could still be used as it is High repetition rate operation/fracture/thermal lensing to be studied Non steady-state operation and pre-pumping to be tested It would also be a useful source for cathode studies Commercial oscillator+ pre-amplifier+ harmonic stages is available (up to 30 W in the IR ~15 W in green without amplification) • ~200 k. Euro • 4 months from order • 3 months for tender • After proof of new configuration for CALIFES laser Marta Csatari Divall CTF 3 Collaboration meeting 6 th May 2010 Photo-injector laser for CTF 3

Feasibility for CLIC laser Current amplifiers in a pre-pumped mode with a pre-shaped pulse Pre-shaped input pulse Steady state operation with an additional amplifier After 1 st amplifier After 2 nd amplifier By Mikhail Martyanov from IAP • ~20 k. Euro • 3 -4 months development for driver electronics • 5 weeks testing • In collaboration with IAP • Stability can be an issue • We are working well above saturation fluence • We are close to fracture limit • Slab amplifier might be better solution • Further feasibility is required in 2010/2011 • 1 year for tender for diodes/drivers and chiller • With original design 600 k. Euro • STFC doing feasibility for SLAB geometry Marta Csatari Divall CTF 3 Collaboration meeting 6 th May 2010 Photo-injector laser for CTF 3

Future plans 2010 • Detailed noise measurements (laser and PHIN) • Improved laser environment by autumn • Implementation and test of phase-coding 2011 • Implementation and test of feedback stabilization system • Noise measurements on the machine • Long train harmonics stages • Design studies for CLIC laser Marta Csatari Divall CTF 3 Collaboration meeting 6 th May 2010 Photo-injector laser for CTF 3

Thanks for all, who contributed ! CTF 3 Collaboration meeting 6 th May 2010

Harmonic stages Mikhail Martyanov, Grigory Luchinin, Vladimir Lozhkarev IAP KDP-I, 82 10 mm 7. 5 mm ADP-I, 90 20 mm 50% conversion efficiency 4 th harm. efficiency 0. 24 0. 23 0. 21 0. 39 40% conversion efficiency G. CHEYMOL- M. GILBERT CEA Pulse Picker bypass for PHIN Marta Csatari Divall CTF 3 Collaboration meeting 6 th May 2010 Photo-injector laser for CTF 3

Noise response Effect of 100 k. Hz seed modulation on the output (PILOT laser 2004 ) • Response time of the amplifier will depend on the gain and the relaxation time and output fluence • Fast input variations will not be damped Marta Csatari Divall CTF 3 Collaboration meeting 6 th May 2010 Photo-injector laser for CTF 3

Steady-state MOPA How is the output power affected by the input parameters? Pumping diodes Current overshoot <1% Ripples <1% Temperature Oscillator and preamp from High. Q < 0. 2 % rms above the 100 k. Hz noise region <1% rms below the 100 k. Hz noise region Interlinked with all the others • The best technology for the time was bought • We are more sensitive to pump variation • Stabilized diode technology should be investigated • 0. 33% RMS stability is measured in the IR Marta Csatari Divall CTF 3 Collaboration meeting 6 th May 2010 Photo-injector laser for CTF 3

Photo-injectors around the world Marta Csatari Divall CTF 3 Collaboration meeting 6 th May 2010 Photo-injector laser for CTF 3

Long train test bench • Using the rejected beam after 1 st Pockels-cell • This would allow us to do independent tests during CALIFES operation • Long train studies on the harmonic stages should be done with existing amplifiers • Feedback stabilization and stability measurements could be carried out at different wavelengths ~30 k. Euro for hardware 2 -3 months for stability measurements (starting summer 2010) Specification of feedback stabilization system (by end of 2010) 4 -6 weeks harmonics studies and fracture limit test (September 2010) 2 -3 months crystal temperature stabilizer development 2 months feedback stabilization with new electronics (by spring 2011) Starting summer 2010