Transient processes in photocathodes at high laser intensities

The transient characteristics of a photocathode observed following the inst antaneous onset and termination of optical excitation in one- and two-pulse excitation regimes are considered within a nonlinear diffusion model. The critical values of the illumination intensity corresponding to the manifest ation of charge-confinement effects and to the cessation of photoelectron e mission are determined. It is shown that the emission charge in a pulse is a nonmonotonic function of the excitation intensity and depends strongly on the values of the negative electron affinity and the effective transparenc y of the barrier in the activation layer. In the charge-confinement regime the time for establishing a stationary photovoltage and emission current fo llowing the onset of excitation is determined mainly by the establishment o f equilibrium between the electron and hole fluxes reaching the surface and is inversely proportional to the illumination intensity. The time for rest oration of the photocathode characteristics following the termination of il lumination is inversely proportional to the trapping rate of holes on deep neutral centers during their tunneling to the surface through the barrier i n the space-charge region and can be as large as several microseconds. (C) 1998 American Institute of Physics. [S1063-7826(98)01112- 0].