Thermal emittance and lifetime of alkali-antimonide photocathodes grown on GaAs and molybdenum substrates evaluated in a -300 kV dc photogun

Cs_{x}K_{y}Sb 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 1 um), yielded similar thermal emittance per rms laser spot size values (∼0.4 mm mrad/mm) 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.