Abstract：Two-photon fluorescence excited spectrum of NO induced by Nd:YAG laser pumped optical parameter generator/amplifier as excitation source was obtained in the range of 420-472 nm. With this technique, the structure of the energy levels of NO molecule in A2Σ electronic state was investigated. The peaks of the spectrum were attributed to A2Σ(v′=0,1)←X2Π(v″=0) transition. The near square dependence of fluorescence signal on the laser intensity indicates a two-photon process. The ground-vibrational-state oscillation frequency and the force constant of A2Σ state were calculated. The fluorescence lifetime of A2Σ(v′=0) state under the pressure of 266 Pa was also obtained by measuring fluorescence decay curve of A2Σ(v′=0) states. It is about 53.76 ns. Fitting the curve of the fluorescence radiant lifetime versus pressure, the spontaneous radiant lifetimes and the rate coefficient of nonradiative transition relaxation of A2Σ(v′=0, 1) states were deduced.
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