强激光诱导NO分子的多光子光声光谱

以Nd∶YAG激光器抽运的光学参量发生/放大器为激发源,采用脉冲光声（PA）光谱技术,获得了NO分子在420.0～470.0 nm波长区间的激光诱导光声光谱,光谱由规则的振动序列组成。通过测量光声信号随激光强度的变化,确定了光声信号产生于NO分子经X^2Π（v″=0）→A^2Σ（v′=0,1）的双光子激发跃迁及X^2Π（v″=0）→E^2Σ（v′=2,3,4）,F^2Σ（v′=1,2,3）,R^2Σ（v′=0,1）的三光子激发跃迁,对应于双光子激发跃迁的光声信号比通过三光子激发跃迁产生的光声信号强,由此确定了以可见光作激发光源,采用光声技术对NO分子进行探测的最佳激发波长为452.4 nm或429.6 nm。以实验结果为基础,获得了NO分子A^2Σ,E^2Σ,F^2Σ,R^2Σ激发电子态的振动常数分别为2346 cm^-1,2342 cm^-1,2397 cm^-1,2381 cm^-1,与采用其他方法测量的结果符合得较好。

Intense Laser Induced Multiphoton Photo-Acoustic Spectrum of NO

The laser-induced photo-acoustic (PA) spectrum of NO molecule in the wavelength region of 420.0～470.0 nm is collected with an optical parametric generator and amplifier pumped by an Nd:YAG laser as excitation source. The spectrum is composed of regular progression that comes from the excitation of X2Π(v″=0)→A2Σ(v′=0,1) and X2Π(v″=0)→E2Σ(v′=2,3,4), F2Σ(v′=1,2,3), R2Σ(v′=0,1). The variation of PA signal versus laser intensity indicates that these transitions are realized via two- or three-photon process. The signal corresponding to the two-photon process is stronger than that of three-photon process. So the optimum excitation wavelengths are 452.4 nm or 429.6 nm to detect NO with the technique of PA and with visible light as excitation source. Based on experimental data, the vibration constants of NO A2Σ, E2Σ, F2Σ and R2Σ excited electronic states are calculated from the wavelength of the spectral peaks. They are 2346 cm-1, 2342 cm-1, 2397 cm-1 and 2381 cm-1 respectively, and agree well with results by other methods.