光学厚Rb蒸气界面附近后向荧光光谱研究

在存在表面耗散层的纯Rb光学厚蒸气中，利用小功率可调谐半导体激光器泵浦Rb(5P_3/2)的超精细结构能级，测量和分析了780 nm(5P_3/2→5S_1/2)和795 nm(5P_1/2→5S_1/2)后向荧光的强度和线形，耗散层(近区)起光谱滤波器的作用。有两种可能产生5P_1/2态原子的机制，第一种机制是Rb(5P_3/2)+Rb(5S_1/2)→Rb(5P_1/2)+Rb(5S_1/2);第二种机制是Rb(5D)+Rb(5S)→Rb(5P)+Rb(5P)，对于每一种机制，给出了后向敏化荧光的理论公式。研究后向荧光时，必须要确定荧光强度与激光功率的关系和荧光线形。激光频率扫描超精细结构共振线，得到的敏化后向荧光795 nm线形与共振荧光780 nm线形相似，其荧光强度与荧光功率有线性关系。因此，基本上可以用第一种机制解释5P_1/2态布居机制。理论证明了，第二种机制产生的敏化后向荧光强度应与激光功率平方成比例，这与实验结果是不同的，第二种机制不能解释耗散层界面后向敏化荧光的产生。

Spectroscopic Investigation of Retrofluorescence in a Pure Optically Thick Rb Vapour Near the Surface

A low-power tunable laser was used to populate the Rb(5P3/2)hyperfine-structure levels in a pure optically thick vapour in the presence of a dissipative surface. The retrofluorescence intensities and spectrum profile for the 780 nm (5P3/2→5S1/2)and 795 nm (5P1/2→5S1/2)lines were measured and analyzed. The glass-vapor interface was considered as two distinct regions, a wavelength-thickness vapor layer adjacent to the surface and a more remote vapor region. The first region was analyzed as a spectral filter that annihilated the absorbed photons and the second one as a rich spectral light source. The authors discussed two possible mechanisms for the 5P1/2 population in the cell［i.e., mechanism(1):collisions Rb(5P3/2)+Rb(5S1/2)→Rb(5P1/2)+Rb(5S1/2); mechanism(2): collisions Rb(5D)+Rb(5S)→Rb(5P)+Rb(5P)］. For each one of the possible mechanisms considered, the authors gave the theoretical formulation of the retrofluorescence integrated signal associated with 795 nm(5P1/2→5S1/2), which was compared with experiment. Two important characteristic aspects of retrofluorescence spectra must be taken into account when dealing with retrofluorescence signals for atomic process investigation: the retrofluorescence intensity dependence on laser power and sensitized laser retrofluorescence line shapes. When the laser frequency is scanned through the hyperfine resonance line, the sensitized retrofluorescence spectra signal corresponding to the 795 nm line has a profile similar to the profile of the retrofluorescence signal at the 780 nm. The authors have pointed out that mechanism(1)gives the linear dependence of the trtrofluorescence as a function of laser power and the spectrum profile. The population of the 5P1/2 atomic level in an optically thick vapour can be principally explained by the fine-structure excitation transfer process ［mechanism(1)］. It appears from our experimental and theoretical investigations that, the spectral properties of the laser-induced Rb 795 nm sensitized retrofluorescence in a pure optically thick vapour near a dissipative surface cannot be explained by the mechanism(2).