Shock-Wave Generation in Rarefied Gases by Laser Impact on Beryllium Targets

Abstract

Shock waves in argon and in air have been observed when focusing a 0.8 J, 40 nsec, Q-switched ruby laser beam onto a beryllium target in the presence of gas at various pressures ranging fron 2×10−1 to 3 Torr. High-speed streak and framing camera as well as a prism spectrograph have been used as diagnostic tools. Space-resolved spectra show, besides an intense continuum, Stark-broadened lines from Be I and Be II. The reinforced argon lines when moving off the Be target surface are probably due to a shock wave driven by the Be plasma acting as a piston. A simple theoretical model taking this mechanism into account is proposed. Calculated curves for the outer radius variations of the shock front fit closely the experimental results.