Thermal emittance and lifetime of alkali-antimonide photocathodes grown on GaAs and molybdenum substrates evaluated in a <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mo>−</mml:mo><mml:mn>300</mml:mn><mml:mtext> </mml:mtext><mml:mi>kV</mml:mi></mml:mrow></mml:math> dc photogun
Y. Wang, M. A. Mamun, P. Adderley, B. A. Bullard, Joseph Grames, J. Hansknecht, C. Hernandez-Garcia, R. Kazimi, G. Krafft, G. Palacios-Serrano, M. Poelker, Marcy Stutzman, R. Suleiman, Michael Tiefenback, Sajini Wijethunga, Joshua Yoskowitz, S. Zhang
Abstract
${\mathrm{Cs}}_{x}{\mathrm{K}}_{y}\mathrm{Sb}$ photocathodes grown on GaAs and molybdenum substrates were evaluated using a $\ensuremath{-}300\text{ }\text{ }\mathrm{kV}$ dc high voltage photogun and diagnostic beam line. Photocathodes grown on GaAs substrates, with varying antimony layer thickness (estimated range from $<20\text{ }\text{ }\mathrm{nm}$ to $>1\text{ }\text{ }\mathrm{um}$), yielded similar thermal emittance per rms laser spot size values ($\ensuremath{\sim}0.4\text{ }\text{ }\mathrm{mm}\text{ }\mathrm{mrad}/\mathrm{mm}$) 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.