Energy deposition of pulsed one micron laser radiation in H2 and AR

In RP (repetitively-pulsed) laser propulsion the propellant energy is supplied by the absorption of short, repetitive laser pulses beamed to the thruster from a remote laser power station. The four principal stages in the operation of the pulsed laser-heated thruster are as follows: (1) ignition/breakdown, (2) post-breakdown plasma absorption and growth under the influence of the laser radiation field, (3) blast wave propagation into the surrounding gas, and (4) late-time expansion and cooling of the laser-heated gas. In a previous study at PSI experimental and theoretical investigations of laser-induced gas breakdown at short laser wavelengths ( 1 micrometer) were carried out for a variety of propellant gas candidates. The results of those studies have helped to establish the threshold irradiances required to initiate an optically absorbing plasma. Experiments were performed to investigate the degree of laser optical absorption and the resulting plasma-dynamics which occurs when high energy pulses of 1.05 micrometer laser radiation are focused into various gases at focal intensities above the breakdown threshold (10 to the 10th power 10 to the 13th power w/sq cm).