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 spectrescopically with a time resolution of 40 ns. Measured line profiles of several ionic species (CI-CIV) were used to infer electron density and temperature at several positions above the target surface as function of time elapsed after the beginning of the laser pulse. The particle density at several positions above the target surface as function of time was judged from corrected line intensities. Experimental data are compared with theoretical predictions made with the effusion model of plasma expansion [Kelly, R. and Braren, B., Appl. Phys. B53, 160 (1991)]. The effusion model provided the relative particle density in the expanding plasma cloud as a function of initial target temperature. By comparing predicted and measured time evolution of particle density, an initial target temperature of about 125 eV was inferred. The coupling of the laser beam energy to the plasma itself was inferred from the failure of the model of the direct target surface heating [Andreic, Z., Henc-Bartolic, V. and Kunze, H.-J., Physica Scripta 48, 331 (1993)] to produce the required target temperature.