Y thin films by ultra-short pulsed laser deposition for photocathode application

In this work, the deposition of Y thin films by laser beams with 0.5 ps and 5 ps pulse durations at different laser fluences (1.2-6.4 J/cm(2)) is reported. The morphology of the deposited films and of the ablated target surface is investigated by scanning electron microscopy analyses. The present results show that the films, well adherent to the substrates, are characterized by a high abundance of sub-micrometric particulates with average size less than 0.3 mu m, whose density decreases with increasing laser fluence. The formation of columnar structures observed on the target surface seems to be responsible of the poor film homogeneity. Acceptable deposition rate in the range of 0.08-0.16 A/pulse with 5 ps pulse duration is found; on the contrary with 0.5 ps pulse duration, it is not possible to get information on deposition rate as a function of the laser fluence due to the high non-uniformity of the films. A comparison with the results previously obtained in ns regime is presented and discussed. The achievements of our investigation will be useful to optimize the synthesis of photocathodes based on Y films for the production of bright electron beams in radio-frequency photoinjectors.