Quantum Efficiencies of Mg Photocathode under Illumination with 3rd and 4th Harmonics Nd: LiYF4 Laser Light in RF Gun

A Mg photocathode for use in a radio-frequency gun was manufactured by a technique of hot isostatic pressing with diamond polishing and tested under a peak electric field of 57 MV/m. A laser cleaning process for the Mg cathode was developed. The quantum efficiency (QE) of the Mg cathode before and after the laser cleaning was measured under illumination with 262 nm and 349 nm laser light. A high QE of up to 1.0×10-3 was achieved under the 262 nm laser-light illumination. The QE of the Mg cathode under the 349 nm laser-light illumination was measured to be 2.2×10-5. The dependence of the QE on the electric field was measured and compared with a theoretical analysis including the Schottky effect.