Driving circuits for copper halide lasers-a parametric study

Abstract

The influence of circuit inductance and current rise-time on the performance of a longitudinally excited copper halide laser was investigated for (a) double spark gap and (b) thyratron burst-mode driver circuits with low inductance configurations. The inductance of the circuit of the dissociation spark gap was not critical and the output of the laser increased as the inductance of the laser-pulse spark gap circuit was decreased to its minimum value. The effectiveness of the driver circuit was limited principally by the long extinction time of the dissociation spark gap, which restricted the interpulse delay time to values considerably in excess of the intrinsic delay for the laser itself. For the lowest inductance (about 65 nH) of the thyratron burst-mode circuit, the duration of the current pulse is limited by the finite speed of propagation of ionisation waves in the laser discharge tube rather than the inductance and the rate of rise of current in the thyratron significantly exceeds the tube rating. An L-C inverter circuit is described which removes the thyratron from the laser discharge circuit but it is found that the inversion time must be matched to the current growth in the laser tube and this requires the addition of inductance to the thyratron circuit. The most critical factor in determining the pulse energy available from the laser is the restriction on the rate of current rise for presently available thyratrons.