Time- and space-resolved diagnosis of laser ablation plasma probed by optical transmittance

Time- and space-resolved optical transmittance has been observed for the plasma generated by pulsed laser ablation of Ca, Sr and Ba targets. A Gaussian distribution dynamic model including center-of-mass motion has been proposed to simulate the process of plasma expansion. The simulation shows that ratios of specific heat capacities at constant pressure and volume γ are 1.05, 1.10 and 1.15 for the ablation plasmas of Ca, Sr and Ba, respectively. These values are much smaller than that of an ideal gas. It is ascribed to the recombination and de-excitation processes taking place in the plasma.