P. Miglietta

Photoemission characteristics of PLD grown Mg films under UV laser irradiation

In this paper we report a detailed description of the laser cleaning procedure and emission performance measurement on a pulsed laser deposited Mg film. During the tests performed after the end of each cleaning operation we have observed an increase in quantum efficiency (QE) in time. Then the QE apparently stabilizes at a remarkably higher value. The study of this phenomenon and its relation to chemical composition of the residual gases of vacuum environment is important because it determines both the achievable QE value and the lifetime of the Mg film based cathode. Moreover, the stability of the QE at remarkably high values has been revealed for a time scale of several days after each laser cleaning process, in our vacuum conditions. The adsorption of reactive chemical species leading to the lowering of the Mg work function is discussed.

Photoelectron performance of Y thin films and Y smooth bulk cathodes

New photo-injector sources having fast response time, long lifetime and relatively high-quantum efficiency (QE) are very needed for many applications. Metallic cathodes are promising candidates to supply high-intensity and good quality electron beams. We carried out measurements utilising thin films and a smooth bulk made of yttrium (Y). The Y thin films were produced by pulsed laser deposition (PLD, using a XeCl excimer laser) in high vacuum. It was covered, in situ, by a gold film to avoid oxidation. The Y smooth bulk was mechanically processed in air. The laser used to get experimental values of photoemission was a KrF excimer laser of 5 eV photon energy and 23 ns pulse duration. The maximum accelerating voltage applied to the photodiode (the anode) was+25 kV. The measurements of photocurrent were performed at different laser energies. We found that the output current was depended on the cathode surface. The higher QE values were obtained for the smooth cathode. It provided a maximum output current of 8.4 A, at 25 kV and 12 mJ laser energy. The maximum QE was 7.0×10−5.