Thermal Emittance and Lifetime of Alkali-Antimonide Photocathodes Grown on GaAs and Molybdenum Substrates Evaluated in a -300 Kv Dc Photogun

CsxKySb photocathodes grown on GaAs and molybdenum substrates were evaluated using a -300 kV dc high voltage photogun and diagnostic beam line. Photocathodes grown on GaAs substrates, with varying antimony layer thickness (estimated range from <20 nm to >1 um), yielded similar thermal emittance per rms laser spot size values (similar to 0.4 mm mrad/frun) but very different operating lifetime. Similar thermal emittance was obtained for a photocathode grown on a molybdenum substrate but with markedly improved lifetime. For this photocathode, no decay in quantum efficiency was measured at 4.5 mA average current and with peak current 0.55 A at the photocathode.