The investigation of DC electrical discharges by the laser-gas interaction

Laboratoire d'Électronique des Gaz et des Plasmas, Université de Pau, 64000 Pau, France

Received: 26 September 1997
Revised: 31 March 1998
Accepted: 31 March 1998
Published online: 15 August 1998

Abstract

It is shown that the production of electrons by the laser-gas interaction, described in a previous paper [1], at a given position in the interelectrode gap of a DC electrical discharge, is responsible for a transient current associated to the displacement of the running point on the current-voltage characteristic. A theoretical model of the laser-induced current impulse, in good agreement with experiments, is proposed in the case of homogeneous field. Some macroscopic coefficients, like first and second ionization coefficients, or electrons and ions velocities, are examined. The estimated values are compared with ones found in the literature. The theory in homogeneous field, well supported by the experiments, allows to give a qualitative interpretation to the laser-induced current impulse in inhomogeneous field (point-to-plane geometry). 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 shown that the laser-gas interaction is an accurate and effective technique for the investigation of the fundamental processes involved in each electrical state of the discharge (townsend discharge, self-sustained discharge, glow discharge) and in the transition from a state to another (for example, avalanche-to-streamer transition).