Enhanced quantum efficiency of metal/metal compound photocathode irradiated by two wavelengths of Nd:YAG laser

Abstract Metals or metal compounds as photocathodes provide high current density and have high damage threshold for laser irradiation. In addition, the quantum efficiency of these cathodes are enhanced by heating up [1]. The tungsten photocathode heated up to 1400 K and irradiated by 2ω (532 nm) of Nd:YAG laser produced the electron beam with high current density (∼1 kA/cm 2 ) and quantum efficiency was about 10 −5 . In order to further improve the quantum efficiency of the tungsten, it is necessary to instantly increase the temperature above 1400 K without thermal damage of RF gun. Fundamental (1064 nm) of Nd:YAG laser that is uncoverted portion of the laser pulse can heat up the cathode instantly. When the fundamental of 20 ps pulse length irradiates the cathode, peaked temperature is estimated to be after 11 ps of the peak of laser pulse. We irradiated the tungsten photocathode by two wavelengths with time interval between ω and 2ω.