7A8 - Spectroscopic studies of laser-produced hydrogen plasma

Abstract

Time-resolved spectroscopic measurements were made of the decay of a laser-produced discharge in hydrogen over a range of pressures from one to 70 atmospheres. The plasma temperature, which ranged from about 10⁵to10^{4}\degK during theQ-switched laser pulse to several microseconds afterward, was obtained from the ratio of the intensity of Hαto that of nearby continuum radiation. The electron density, which ranged from about 10¹⁹to 10¹⁷per cm³was obtained from the time history of the Stark linewidths of HαSince the high collision rates ensure approximate local thermodynamic equilibrium, several important characteristics of the plasma could be calculated from the measured temperature and density, such as optical absorption at the laser frequency due to inverse bremsstrahlung and photoionization. The energy deposited by the laser was measured from the decrease of the transmitted laser beam. Scattered radiation seemed small. The observed laser absorption is about two orders of magnitude larger than that calculated for a Maxwellian electron distribution. The calculated line absorption for Hαwas consistent with self-absorption observed in the Hαspectral profile. The ratio of the measured watts of Hαto the calculated watts/cm³yielded values for the volume of the luminous region which generally decreased with gas pressure from 10^-3to 10^-4cm³, as observed.