Temporal Response Measurements of GaAs-Based Photocathodes

It is well known that a negative electron affinity GaAs photocathode shows a moderate temporal response when excited by a laser pulse of wavelength close to its band gap energy. We show here that the temporal response can be estimated using a diffusion model that describes the internal transport of the conduction electrons. Using a transverse deflection cavity system, we measured the temporal profile of the electron bunch generated by a DC photocathode gun illuminated by a ps pulsed laser. A systematic set of measurements of GaAs cathodes with various active layer thicknesses and boundary conditions confirmed that the observed temporal response is well understood by the diffusion model calculation.