ANALYSIS OF THE LASER-PRODUCED CURRENT IMPULSE BELOW THE BREAKDOWN THRESHOLD IN A HOMOGENEOUS FIELD

It is shown that a laser beam (lambda = 308 nm, h nu = 4.00 eV) of 17 ns pulse duration transversely directed on the axis of a parallel-plat es device far below the breakdown threshold produces a current impulse in the external circuit. The analysis of the electrical signals, base d on the Ramo-Shockley theorem, allows one to estimate the number N-0 of electrons moving in the gap and their velocity. It is shown that th is velocity is characterized by two components: the drift velocity dep ending on the reduced electrostatic field (E(0)/p) and the other resul ting from the spatial distribution of electrons. Even if N-0 is estima ted, experiments show that, for pressures lying in the range 100-600 T orr, the physical processes responsible for the production of electron s when the laser beam crosses the gap are not only multiphoton transit ions.