-Care CERN 2-5 December 2008 Giancarlo Gatti Phin activities at LNF

-Care CERN 2-5 December 2008 Outline SPARC project overview SPARC drive laser system IR shaper comparison for flat top laser pulse IR/UV-pulse shaping Laser to RF synchronization schemes Trasverse shaping considerations Conclusive remarks 2

-Care CERN 2-5 December 2008 : MiUR Strategic Research Programs Goals: High brightness linac to drive advanced FEL experiments And further experiments

-Care CERN 2-5 December 2008 SPARC commissioning phase 1: low energy e-beam characterization 4

-Care CERN 2-5 December 2008 Sparc phase 2 After gun commissioning in 2006: -Commissioning of downstream linac in progress. -Variable gap undulators installed and ready..... Last minute breaking news: First beam inside undulators

-Care CERN 2-5 December 2008 Photocathode drive laser Demands: Solutions: Emittance minimization Flexibility (Long./Trasv.) Stable reliable operation High current (100 A) from Cu cathode Synchronization rf laser < 1ps rms stable laser performance 6 High energy laser ( uJ) pulses at 266 nm Uniform time and and transverse laser profile: 6-12 ps duration, rise time, 2 mm hard edge

-Care CERN 2-5 December 2008 SPARC laser system: topology Ti:Sa laser composed by: 12 nm bandwidth oscillator IR pulse shaper CPA amplifiers third harmonic generator UV stretcher (used as shaper) Transport to the cathode 7 Proc. PAC 2007 TUPMN040 time shaper

-Care CERN 2-5 December 2008 SPARC laser system oscillator pumps amplifiers Harmonics generator UV stretcher Pulse shaper 8 The laser delivers 5-12 ps, 100  J pulses at 266 nm with a rep. rate of 10 Hz. Energy jitter (5% rms), pointing stability (<50  m) and synchronization respect to the RF (<2ps rms) Several subsystems have been integrated: IR pulse shaper, tranverse unifom pulse selection and imaging system to the cathode.

-Care CERN 2-5 December 2008 Laser temporal pulse shaping M. Petrarca S. Cialdi C. Vicario Outline: -IR shaper comparison (a.o. Filter, LCM) -Overall system performances -UV shaper

-Care CERN 2-5 December 2008 Tests of two IR pulse shapers 10 Dazzler Half-waveplate Dazzler Half - wave plate From oscillator Into amplifier Telescopes Phase mask Lens Gratin g From oscillator Into amplifier 60 cm 15 cm DAZZLER LC-SLM

-Care CERN 2-5 December 2008 IR programmable pulse shapers 11 DAZZLER LC-SLM Fast mode Slow mode Acoustic grating Acousto-optic interaction in a TeO 2 crystal

-Care CERN 2-5 December 2008 The UV time profiles the two shapers: DAZZLER LC-SLM 12 Rise and fall time ~ 2.6 psRise and fall time ~ 2.1 ps Opt. Lett. 31, 19 (2006) LC-SLMDAZZLER The spectral shape after the UV stretcher is very similar to the temporal profile

-Care CERN 2-5 December 2008 IR shapers Features: DAZZLER LC-SLM Compact Easy alignment Simultaneously phase & amplitude modulation Losses within 50% Resolution = 0.3 nm Slow optimization Not-compact Not easy alignment Phase only modulation Losses within 50% Resolution<0.1 nm Fast optimization 13

-Care CERN 2-5 December 2008 THG distortions: main limitation for fast rise time A large enough pulse width (≥0.6 ps) is needed to preserve the square spectrum throughout the THG IR pulse length [ps] Measured (solid) and simulated (dots) harmonics spectra C. Vicario et al, Opt. Lett, 31,2006, 2885 The UV spectral shape as function of the input IR pulse length

-Care CERN 2-5 December 2008 UV pulse shaper The UV stretcher was designed to perform several tasks 1. Lengthen the laser pulse proportional to bandwith up to 20 ps. 2. In the Fourier plane an amplitude filter, such as an iris, can be applied to cut the tails of an almost square spectrum produced bu the DAZZLER or LC-SLM, the obtained spectrum profile is transferred into the time profile by the stretcher 3. A on-line spectrometer is integrated Appl. Opt. 46, 22 (2007) 4959

-Care CERN 2-5 December 2008 Picture of the UV shaper 16 Spectrom CCD Focusing lenses Filter plane input output Grating pair

-Care CERN 2-5 December 2008 Cross-correlated UV profile 1 17 Simulation experiment Simulation experiment FWHM 10 ps: experim. vs simulation FWHM 15 ps rise time 1.5 ps

-Care CERN 2-5 December 2008 Measured UV profile 2 for several pulse length 18 UV shaper allows for fast rise time despite of different chirp factors in the stretcher

-Care CERN 2-5 December 2008 Shaping without the IR filter  When a proper sharp cut is applied to the natural UV Gaussian laser spectrum, a flat top profile in time can be produced.  Results are comparable to the two stages pulse shaping.  Price to pay 20% higher energy losses  Cheaper and simpler respect to the other IR pulse shapers  The rise and fall time are reduced to ~1.5 ps (limited by the bandwidth) 19

-Care CERN 2-5 December 2008 No IR shapers: simulations 20 spectra Time shape IR shapeNo IR shape

-Care CERN 2-5 December 2008 Experimental results 21 Appl. Opt. 46, 22 (2007) Spectra No-cut Time Measured (red) and Simulated (black) Cut applied

-Care CERN 2-5 December 2008 Exotic applications: UV multipeaks generation With a grid in the fourier plane we obtained 4 peaks pulse (FEL microbunching enhancement) 22

-Care CERN 2-5 December 2008 Laser to RF synchronization M. Bellaveglia, S. Gallo, C. Vicario

-Care CERN 2-5 December 2008 Synchronize the laser and RF Laser to RF synchronization is needed to have photoinjector optimal and stable operation Photoelectron gun phase < 1 deg rms for emittance compensation Velocity bunching, pulse compression and laser acceleration demands for a tighter specification (100 fs) Laser oscillator Cavity length control Pulse selection amplification THG+ stretcher Laser to the cathode Measure Δf Master clock RF chain

-Care CERN 2-5 December 2008 Phase noise at oscillator level Measurements set up and results 350 fs rms

-Care CERN 2-5 December 2008 UV time jitter: measure at 10 Hz  wave reference Active feedback RF phase shifter Time of arrival jitter estimated with the RF deflector is 390 fs 0.67 ps rms over 6 hours Pill box cavity HV Photo diode mixer Laser Phase noise detection acquisition

-Care CERN 2-5 December 2008 Toward next step: Laser-driven RF To reduce the time jitter we can synthesize the RF frequency from a photodiode excited by the oscillator pulses.To reduce the time jitter we can synthesize the RF frequency from a photodiode excited by the oscillator pulses. The value measured can be affected by the apparatus resolution, shortly more detailed characterizationThe value measured can be affected by the apparatus resolution, shortly more detailed characterization This technique is applicable to lock for 1 laser systemThis technique is applicable to lock for 1 laser system All-optical synchronization system and clock distribution to go at sub 100 fs levelAll-optical synchronization system and clock distribution to go at sub 100 fs level

-Care CERN 2-5 December 2008 Sparc P1 highlights B=6*10 13 A/m*rad First ever emittance oscillation Square laser at the cathode PRL 99, (2007) Opt. Lett. 31, (2006) 2885 Appl. Opt. 46, 22 (2007) 4959 REV. SC. INSTR. 77, PRST- AB 11, (2008)

-Care CERN 2-5 December 2008 E:beam experimental results The flat top pulse shape allowed the observation of the double- minimum emittance evolution at SPARC (only predicted by the theory) °RF phase 0.45 mmrms spot size 5, 1.5 psDuration, rise time 5.5 MeVenergy‏ 100 Acurrent PRL 99, (2007) UV LASER

-Care CERN 2-5 December 2008 Gaussian vs flat beam:comparison 30

-Care CERN 2-5 December 2008 Recent advances: Trasverse shaping Main demands: -Squared beam -Power efficiency Final choice: Telescope system to map Gaussian into flat top Pros: above 70% efficiency (up to 95%) Cons: exact matching of TEM 00 gaussian alignment stability filtering cuts real efficiency 2 kinds of commercial refractive Systems probed.

-Care CERN 2-5 December 2008 OUTPUT BEAM INPUT BEAM Our choice: No spatial filter

-Care CERN 2-5 December 2008 Trasportation up to cathode Shape is preserved through relay imaging trasport (10 mt.)

-Care CERN 2-5 December 2008 Conclusions Extensive development on laser pulse shaping has been done at LNF-SPARC within the PHIN collaborationExtensive development on laser pulse shaping has been done at LNF-SPARC within the PHIN collaboration ▫The two stages pulse shaping for 1.5 ps rise time ▫Demonstration of UV-only pulse shaping ▫Work on faster rise time and reduced losses Sub ps synchronization with upgrade at < 200 fs has been demonstratedSub ps synchronization with upgrade at < 200 fs has been demonstrated E-beam results encouraging the search of flat top pulse, definitive comparison at higher energyE-beam results encouraging the search of flat top pulse, definitive comparison at higher energy Complete shaping in the next future when charge issues will be overcome.Complete shaping in the next future when charge issues will be overcome. 34