TIME-RESOLVED EMISSION-SPECTRA FROM LASER-INDUCED PLASMA IN SODIUM-CHLORIDE

Spectroscopic investigations are carried out on the radiation emitted from laser-induced plasma on a NaCl crystal surface. It is found that all atomic lines emitted from plasma produced by laser irradiation in air are broadened and some of them are self-reversed, while the self-r eversal is not observed for plasma induced in vacuum. Self-reversal oc curs for the pressure of ambient gas above 1.3 kPa. It is found from l ine broadening, mainly caused by resonance and the Stark effect, that the Na atom concentration in the plasma is 5.3 x 10(24) m-3. Observed time-resolved spectra agree with a model that the plasma generated by laser irradiation is composed of a hot core and a low-temperature peri phery, both behaving, respectively, as emission and reabsorption cente rs and expanding at a speed determined by the ambient gas pressure.