Kinetics of excited ion levels population in the expanding laser plasma. Comparison between the CARS and spontaneous light data

The kinetics of the spontaneous light and the anti-Stokes signal ωa = 2ω1- ω2 (ω1 is the frequency of the second harmonic of Nd:YAG laser, ω2 is the dye laser frequency), generated in the region of optical discharge plasma produced on the metal target surface by Nd:YAG laser is investigated. The strong lines in the spectra of anti-Stokes emission conditioned by ion resonances of N (II) are registered. Dependence between the CARS signal intensity and the spontaneous plasma light upon the delay in time of the optical spark beginning and the sounding impulses is obtained. An independent laser system of ND:YAG synchronized in time with the sounding radiation is used. The correlation between the moment of the maximum CARS signal and the energy of the impulses provoking optical spark is observed. It is established that the time kinetics of the spontaneous light and the CARS signal intensity are qualitatively different. The obtained results are reproduced by simple quasiequilibrium collisional-radiative model of expanding plasma. 1 ref. (author)