Interaction of CO2 laser radiation with a shock-heated hydrogen plasma

The interaction of a short pulse (1 Joule, 80 nsec FWHM) CO2 laser beam with a dense (n /sub e/ approx. = 1017cm-3), low temperature (T /sub e/ approx. = 1 eV) hydrogen plasma has been investigated. The plasma was produced in an electromagnetic shock tube and lasted for several microseconds. Spectroscopic techniques were used to obtain time resolved electron density and electron temperature measurements. Absorption of the laser beam by inverse Bremsstrahlung was observed for several microseconds after the arrival of the plasma in the interaction area. Partial absorption was observed for many microseconds in the decaying plasma. The electron temperature was observed to increase by amounts up to 0.25 T /sub e/ after absorption of the laser beam. Calculations of plasma heating by inverse Bremsstrahlung indicate that only a small percentage of the absorbed laser energy goes into heating the electrons. The bulk of the absorbed laser energy goes into expansion of the plasma