Time- and space-resolved emission spectroscopy measurements were performed to investigate plasma dynamics during laser evaporation of a graphite target. The evolution of the velocity and the emission intensity of the excited species versus the distance and the pressure of the foreign gas are studied. The time-resolved emission intensity of C II* transition at 426.7 nm shows a double-peak structure, resulting from the stratification of the plasma into fast and slow components. Intense molecular emission is found to occur behind a front separating the plasma from the foreign gas. Two stages of expansion are found in the generated plume, the first one starting just after the laser irradiation, the second beginning some time later depending on the nature and the pressure of the foreign gas. The two stages are well described, using a viscous drag force model for the first one and a delayed ideal blast wave model for the second.

Two kinds of experimental results obtained from time-resolved second-harmonic spectra for 1.06 μm laser-produced plasma are presented. At moderate laser intensities (≤2×1014 W/cm2) the results are explained with parametric and electron decay instabilities. Whereas, at high laser intensities (≥6×1014 W/cm2) the Langmuir strong turbulence is used to explain experimental results. In addition to results obtained by Briand et al. [Phys. Fluids B 2, 160 (1990)], a second sequence of collapses is observed.

An experimental analysis is conducted to visualize sidescattered second harmonic spectra originating from the critical surface of a plasma produced from a 1,064-nm laser beam. It is shown that longitudinal and transverse wave-scattering mechanisms producing the second harmonic may also alter the local plasma parameters. These irregular plasma parameter variations and the perturbed spatial uniformity of the incident laser beam can, in turn, be visualized through the second harmonic behavior. This work confirms the origin of the second harmonic production in an inhomogeneous plasma. Time evolution of the optical density of this harmonic showed spectral shifts due to the Doppler effect related to the critical surface dynamics. On the time-integrated spectra, shifted secondary peaks have been observed, indicating that the second harmonic takes its origin also from parametric decay as well as electron decay instability. Other properties of the interaction physics are deduced from the present second harmonic study.

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Time and space-.resolved emission spectroscopy measurements were performed to investigate plasma dynamics during laser evaporation of a graphite target in an ambient inert atmosphere. Intense molecular emission is found to occur behind a front separating the plasma from the .foreign gas. Two stages of expansion are found and are well described, using a viscous drag force model for the first one and a delayed ideal blast wave model for the second. The vibrational temperature estimated using the Swan band in helium at different pressures is presented.