Enhancement of photoemission from and postprocessing of K_{2}CsSb photocathode using excimer laser

Abstract

The high quantum efficiency at visible wavelengths of alkali-antimonide photoemissive materials, such as K_{2}CsSb, makes them excellent potential photocathodes for high-current applications. We have developed a technique of using an ultraviolet laser to clean the cathode’s substrate and thus enhance the photoyield of a K_{2}CsSb photocathode subsequently deposited on the substrate. We have shown that the quantum efficiency of the cathode from the laser-exposed substrate can be at least 50% higher than that of an unexposed surface. We have also formulated a nonthermal technique for completely removing the cathode from the substrate while preserving an ultrahigh vacuum to assure the regrowth of the cathode. The bialkali cathode is dissociated and then removed completely upon 10 s exposure to a 248 nm laser beam with 3.5 mJ/mm^{2} of energy density at a 30 Hz repetition frequency. Here, we discuss these experimental results and their potential applications. We also describe applications of this technique to reduce the beam’s halo and its emittance.