Advanced electron injectors of last generation are based on photocathode electron guns. These guns can produce electron beams with short pulses and high brightness. Initially the interest in photo-injector development has been mainly driven by Free Electron Laser (FEL) applications, due to the high peak current needed in such systems. But now photo-injectors are also the electron source of choice for next generation accelerator installations. Among the different photo-injector systems the photocathodes play a key role. In strong relation with the laser system the choice of the optimum cathode type and its further improvement is a main issue for the progress in photo-injectors.
We present the results of our investigation of metallic films as suitable materials for the production of intense electron beams. Thin films of Y prepared by pulsed laser deposition on Si and Cu substrates have been investigated and then tested as photocathodes in an ultra high vacuum photodiode chamber at 10-9 mbar. High quantum efficiencies have been obtained for the deposited films, comparable to those of corresponding bulks. The rule of the adsorbed gases on the emission performance has been studied. Systematic laser cleaning treatments improved the quantum efficiency from 10-6 to 4.5 10-4.
The samples could stay for several months in open air before being tested in a photodiode cell. The deposition process and the tests are presented.