A laser pulse shaper for the low-emittance radiofrequency SPARC electron gun

To generate a very low emittance electron beam in a 3-GHz radiofrequency gun, the photocathode has to be driven by a powerful 10-ps light pulse with a rise time of less than 1 ps: This target pulse can be generated from a subpicosecond laser pulse by inserting an appropriate shaping device. We discuss a programmable 4f grating-lensshaper configured so as to transform a 100-fs pulse emitted by a Ti:Sa laser into a rectangular pulse with a fast rise time. We analyze the sensitivity of the system to perturbations of the optical-component alignment and input-signal characteristics. We then briefly discuss the acousto-optic programmable dispersive filter shaping system.