SIMPLE ONE-DIMENSIONAL SIMULATION OF A LASER PHOTOEMITTED ELECTRON BUNCH

The dynamics of a photoemitted charged pulse in a one dimensional photocathode is investigated. At a very short pulse duration, on the order of a few picoseconds, short with respect to the transit time, interesting features are revealed. After a transient period, the charged pulse spreads and becomes uniformly distributed. The pulse spreads approximately to the extent of the transit time in the gap. This behavior is the result of the self-action electric field and depends on the total charge emitted under the laser power, on the pulse length and on the electric field. A one dimensional simulation and an analytic model describe the pulse propagation and are in excellent agreement. At high acceleration fields, in the relativistic regime, different time evolutions result. In the present simulation we make the simplified assumption that the relativistic effect only changes the electron mass. The result is that the self-field is overcome by the relativistic dynamics, and the electron pulse steepens.