Temporal behaviour of photoemission for yttrium cathodes

Abstract

In this work, the photoemission performance of rough and smooth cathodes is presented. The cathodes were made up of pure yttrium metal bulk. For evaluation of the photocathodes, a KrF excimer laser, operating at 248 nm wavelength, 5 eV photon energy and 23 ns full width at half maximum (FWHM) was used. The targets were tested in a vacuum photodiode cell at 10−7 mbar; they were irradiated at normal incidence and the anode–cathode distance was set to 5 mm. The measurements were performed after a series of electric breakdowns between anode and cathode, induced under high laser energy and high accelerating voltage. This operation was performed in order to restore/increase the surface roughness. For the rough cathode, the maximum output current was 10.5 A, reached at 25 kV and 12 mJ laser energy; the maximum quantum efficiency (QE) value was 1.3×10−4, whereas for the smooth cathode, the maximum output current was 8.4 A and the maximum QE value was 7.0×10−5, calculated in the same experimental conditions. The temporal behavior of photoemission from these cathodes was studied. Plasma production and Schottky effect played a fundamental role in this process.