A diffusion model for picosecond electron bunches from negative electron affinity GaAs photocathodes

Even though theoretical estimates predict response times for the photoemiss ion process of electrons from a negative electron affinity GaAs photoemitte r in excess of hundreds of picoseconds, recent measurements found electron bunch durations of 40 ps or less. This work presents precise measurements o f picosecond electron bunches from a negative affinity bulk GaAs photocatho de and develops a model which explains the measured bunch durations as well as the observed bunch shapes. The bunch shape turns out to be independent from the quantum efficiency of the photoemitter. (C) 1999 American Institut e of Physics. [S0021-8979(99)04616-2].