Analysis of the laser-produced current impulse below the breakdown threshold in a homogeneous field

It is shown that a laser beam ( , ) of 17 ns pulse duration transversely directed on the axis of a parallel-plates device far below the breakdown threshold produces a current impulse in the external circuit. The analysis of the electrical signals, based on the Ramo - Shockley theorem, allows one to estimate the number of electrons moving in the gap and their velocity. It is shown that this velocity is characterized by two components: the drift velocity depending on the reduced electrostatic field and the other resulting from the spatial distribution of electrons. Even if is estimated, experiments show that, for pressures lying in the range 100 - 600 Torr, the physical processes responsible for the production of electrons when the laser beam crosses the gap are not only multiphoton transitions.