CO2 laser-induced gas breakdown in hydrogen

Abstract

A single-mode CO2 laser pulse of approximately 10 MW peak power has been used to induce breakdown at pressures from 50 to 700 Torr in hydrogen. Measurements of the reflected and transmitted laser intensity were obtained and the properties of the resulting spark were studied by means of image converter camera and spectroscopic techniques. At pressures in excess of 100 Torr the spark was observed to grow preferentially towards the focusing lens, while at lower pressures a symmetric expansion was observed. The observed motion was consistent with the existence of a breakdown wave during the rising portion of the laser pulse followed by a laser-supported detonation. At pressures greater than 100 Torr, significant reflection (> 2%) was observed during the detonation phase.