ULTRASHORT ELECTRON-EMISSION IMPROVED BY ALKALI IONS IMPLANTATION INTO METALLIC PHOTOCATHODES

The photocathodes we are studying combine the high laser damage thresh old and the long lifetime of metallic photocathodes with the high phot oelectric sensitivity and the low work function of semiconductor ones. They consisted of alkali ion implantation into the metal surface, in particularly tungsten, implanted by potassium ions in 40 nm thickness surface layer. The photoelectric performances at p-polarization and at various angles of incidence using a picosecond Nd YAG laser with tau = 16 ps and lambda = 213 nm. A significant improvement of the photoele ctric sensitivity of K+-implanted W photocathodes have been demonstrat ed, as well as a good stability of the performances during more than 1 00 h irradiation.