Ablated Mg films with a graphite cover as photocathodes

Mg films deposited by pulsed laser ablation on a Cu substrate were tested as photocathodes in a DC diode. They showed features of robustness and a quantum efficiency of 3 10 4 at low accelerating field when illuminated by 266nm light at normal incidence. A graphite protective layer of about 20nm thickness deposited by laser ablation just after the Mg deposition made the cathode stable and of easy handling. The cathodes could stay for several weeks in air before being inserted in the test chamber. The preparation procedure and the tests are presented.