Time-resolved spectroscopic diagnostic of laser-induced plasma on germanium targets

Time-resolved optical emission measurements have been made in laser-induced plasma plumes following CO2 pulsed-laser (10.591 μm, 64 ns and intensity from 0.27 to 4.9 GW cm−2) irradiation of germanium targets. The temporal behavior of Ge atoms and ionized excited species Ge3+, Ge2+, and Ge+ is reported. The results show a faster decay of the continuum emission and Ge3+, Ge2+ ionic species than in the case of Ge+ and neutral Ge atoms. The velocity distributions for Ge3+, Ge2+, Ge+, and Ge species are obtained from time-of-flight measurements. Electron density in the laser-induced plasma was estimated from the analysis of spectral data at various times from the CO2 laser pulse incidence. From the intensity decay with the delay time for Ge+, Ge2+, and Ge3+, we estimated the three-body electron-ion recombination rate constants for these species.