THE INVESTIGATION OF DC ELECTRICAL DISCHARGES BY THE LASER-GAS INTERACTION

It is shown that the production of electrons by the laser-gas interact ion, described in a previous paper [1], at a given position in the int erelectrode gap of a DC electrical discharge, is responsible for a tra nsient current associated to the displacement of the running point on the current-voltage characteristic. A theoretical model of the laser-i nduced current impulse, in good agreement with experiments, is propose d in the case of homogeneous field. Some macroscopic coefficients, lik e first and second ionization coefficients; or electrons and ions velo cities, are examined. The estimated values are compared with ones foun d in the literature. The theory in homogeneous field, well supported b y the experiments, allows to give a qualitative interpretation to the laser-induced current impulse in inhomogeneous field (point-to-plane g eometry). As a result, depending on the location of the running point on the I-V characteristic and on the laser energy available for photon -ionization, it is shows that the laser-gas interaction is an accurate and effective technique for the investigation of the fundamental proc esses involved in each electrical state of the discharge (townsend dis charge, self-sustained discharge, glow discharge) and in the transitio n from a state to another (for example, avalanche-to-streamer transiti on).