DYNAMICS OF LASER-PRODUCED CARBON PLASMA

Carbon plasmas produced by radiation from a ruby laser (wavelength 694 .3 nm) focussed onto a carbon target in vacuum are studied spectrescop ically with a time resolution of 40 ns. Measured line profiles of seve ral ionic species (CI-CIV) were used to infer electron density and tem perature at several positions above the target surface as function of time elapsed after the beginning of the laser pulse. The particle dens ity at several positions above the target surface as function of time was judged from corrected line intensities. Experimental data are comp ared with theoretical predictions made with the effusion model of plas ma expansion [Kelly, R. and Braren, B., Appl. Phys. B53, 160 (1991)]. The effusion model provided the relative particle density in the expan ding plasma cloud as a function of initial target temperature. By comp aring predicted and measured time evolution of particle density, an in itial target temperature of about 125 eV was inferred. The coupling of the laser beam energy to the plasma itself was inferred from the fail ure of the model of the direct target surface heating [Andreic, Z., He nc-Bartolic, V. and Kunze, H.-J., Physica Scripta 48, 331 (1993)] to p roduce the required target temperature.