<title>Production of temporally flat top UV laser pulses for SPARC photo-injector</title>

In the SPARC photoinjector, the amplified Ti:Sa laser system is conceived to produce an UV flat top pulse pro- file required to reduce the beam emittance by minimizing the non-linear space charge effects in the photoelectrons pulse. Beam dynamic simulations indicate that the opti- mal pulse distribution must be flat top in space and time with 10 ps FWHM duration, 1 ps of rise and fall time and a limited ripple on the plateau. In a previous work (1) it was demonstrated the possibility to use a programmable dispersive acousto-optics (AO) filter to achieve pulse pro- file close to the optimal one. In this paper we report the characterization of the effects of harmonics conversion on the pulse temporal profile. A technique to overcome the harmonics conversion distortions on the laser pulses at the fundamental wavelength in order to obtain the target pulse profile is explained too. Measurements and simulations in the temporal and spectral domain at the fundamental laser wavelength and at the second and third harmonics are pre- sented in order to validate our work. It is also described a time diagnostic device for the UV pulses.