Anomalous Absorption in CO2-Laser-Target Interactions

Efficient absorption of long-pulse C${\mathrm{O}}_2$-laser radiation is observed to follow a transient phase of stimulated Brillouin backscatter in critical density, laminar oxygen gas target irradiation experiments. Nearly complete energy absorption occurs for ≲ 10 nsec following stimulated Brillouin backscatter after which target burnthrough and refraction dominate. Inverse bremsstrahlung and resonance absorption cannot account for the general features observed. Anomalous collisions due to strong ion turbulence produced by the incident laser radiation are postulated to account for the efficient absorption.