DEPENDENCE OF PHOTOEMISSION EFFICIENCY ON THE PULSED-LASER CLEANING OF TUNGSTEN PHOTOCATHODES .1. EXPERIMENTAL

This work is related to the study of high density ultrashort electron pulses from metallic photocathodes. This paper deals with the laser cl eaning of a tungsten polycrystalline photocathode. In order to control the surface state of the photocathode, the evolution of the photocurr ent during the cleaning is measured. The experimental set-up comprises a picosecond Nd3+:YAG laser with 5(th) harmonic generator, generating 16 ps duration pulses at 213 nm, with energies up to 0.5 mJ. Experime ntal results concerning the action of laser pulses, as well as the eff ects of residual pressure on the cleanliness of the photocathodes surf ace are presented and discussed. Influence of laser pulses and residua l pressure on the work function of the metal are also investigated.