Plasmon-enhanced photoemission from Au nanoparticles covered with cesiated film

Abstract

The quantum efficiency (QE) and thermal emittance are two main parameters for photocathode, especially for the emission source of free electron laser (FEL) accelerator. It is in challenge how to reduce the rigorous fabrication of cathode and how to enhance the quantum efficiency for photocathode. Facing to the issues in our case, we have investigated plasmon-enhanced photoemission from Au nanoparticles (NPs) covered with Cs film in the microwave electron gun of free electron laser. The large-area preparation and low-cost photocathode are formed by rapid thermal annealing of thin Au films. Cs film covered is found to effectively excite photoelectrons from Au NPs under the visible light (at the 532 nm). The quantum efficiency (QE) of the Au NPs-Cs increases to 2.3 × 10−4 with the pico-second pulsed laser irradiation, and the normalized root mean square (RMS) thermal emittance of the electron beam is about 1.89 mm mrad. It confirms the feasibility for the proposed metallic nanoparticles to be applied to the high brightness electron sources.