Plans for the laser system of the SPARC

Plans for the laser system of the SPARC Frascati test photoinjector SPARC Laser group C. Vicario, A. Ghigo, F. Tazzioli, I. Boscolo, S. Cialdi

Laser performances

Laser layout

Laser pulse simulation -Charge 2 n. C -Peak field in gun 140 MV/m -Pulse shape Flat top -Injection phase 35 deg -Bunch lenght 10 ps -Solenoid field booster 5. 00 k. G -Bunch radius 1. 4 mm -Linac field 25. 25 MV/m -Solenoid field 3. 1 k. G -Energy 155 Me. V -Rms energy spread 0. 16 % -Peak current 185 A en is 1. 3 mm, and does not degrade for: • Phase jitter=one degree RF rms • Emitted charge variation 1% rms (0. 3% IR energy) • Rise-Fall time 1 ps rms

Effect of cathode spot ellipticity on emittance 95% circularity can be obtain with conventional optics (cylindrical lens) enx, eny V. Fusco – Homdyn sim. Ellipticity

Time pulse shaper Phase only modulation preserves optical band To perform pulse stretching!! Specified flat top can be obtained by phase only Modulation (see fig. of non amplified pulse) D. Meshulach, D. Yelin, Y. Silberberge J. Opt. Soc. Am. , B 15 (1998) 1615

Liquid crystal spatial light phase modulator in Fourier plane

Collinear Acousto-Optic modulator (AOM) F. Verluise and al, Opt. Lett. 25, 8 (2000)

Comparison between optical modulators Collinear AOM LC-SLM Variable mask Continuos modulation Discrete, interpixel gaps No critical alignment Crucial LC position 200 nm bandwidth 15 nm bandwidth Not tested for shaping Results (Sumitomo, amplified pulse )

Energy budget Losses: Pinhole flattener 62% Optics 38% 3 th harmonic generation 90% 20 m. J in IR needed to obtain 500 m. J on cathode @ 266 nm and so 1 n. C • Stability of high energy amplified pulses is an issue. • Improvements in cathodes quantum efficiency simplifies the problem.