[Self-absorption of NO fluorescence induced by two-photon]

The two-photon LIDFS of NO excited with 452.4 nm output of an optical parameter generator and optical parameter amplifier pumped by a Nd: YAG laser was obtained. The vibration frequency and the inharmonic coefficients of the ground electronic state of NO were calculated from the results of the spectral ascription. They are omega"e = (1 904. 7 +/- 7. 3) cm(-1), omega"e chi"e = (14.2 +/- 1.2) cm(-1), and omega"e y"e = -(0.021 8 +/- 0.009 1) cm(-1) respectively. It was found for the first time that the intensity of the spectral lines departs from the Frank-Condon principle due to the self-absorption of NO molecules. The spectral line of A 2sigma (v' = 0) --X 2 II (v" = 0) transition disappears in the fluorescence spectra. But it appears gradually with decreasing the sample pressure and the distance from the laser-gas interaction volume to the receiving window. All of these provide an important reference for monitoring NO by the technique of laser-induced fluorescence.