Cs-Ar混合蒸气中6S1/2→6P3/2激光激发的速度选择粒子数密度和饱和效应

Effect of Saturation and Velocity Selective Population in 6S_(1/2)→6P_(3/2) Laser Excitation in Cs Vapor Mixed with Ar

利用一步激发的饱和吸收光谱技术测量了激发态Cs(6P3/2)态的原子密度。室温下的Cs-Ar混合蒸气被852nm激光激发,在6S1/2→6P3/2跃迁线轮廓接近纯Doppler增宽线型、激光线宽远小于非均匀的Doppler线宽而与均匀Lorentz线宽相比的条件下,可以确定基态Cs原子中可能被激光吸收的具有速度分量vz的粒子数密度N(vz)。在激光功率20μW至2.5mW的范围内,测量了吸收系数,得到了6P3/2态的速度选择布居数密度。利用从Cs空心阴极灯发出的8S1/2→6P3/2窄谱线的吸收测量,也可以测得6P3/2态的原子密度,两种测量方法所得结果符合得很好。Cs-Ar碰撞的谱线增宽增加了有效泵浦率,有5%的基态原子被单模半导体激光器激发到6P3/2态。由测量不同6P3/2态原子密度时的共振852nm荧光,也证实了饱和吸收测量激发态原子密度方法的可靠性。

The excited state population distribution created by 6S1/2→6P3/2 laser excitation in room temperature cesium vapor mixed with Ar was quantitatively analyzed applying absorption and saturation spectroscopy. A simple method for the determination of the excited state population in a single excitation step based on the measurements of the saturated and unsaturated absorption coefficients was tested. When the line profile is nearly pure Doppler and the laser linewidth is much smaller than the inhomogeneous linewidth but comparable with homogeneous linewidth, the fraction N（vz） of the atoms in the ground state that are able to absorb under inhomogeneous broadening conditions can be determined. The transmission of the medium in the center of the Doppler envelope of the strong h. f. component of the CsD2 line due to hyperfine pumping alone amounts to ≈5%. The assumption that has been made is that the lower-state hyperfine levels are populated in a statistical ratio. The absorption coefficients were measured for a series of P852 powers between 20 μW and 2.5 mW. The velocity selective population density in the 6P3/2 state was obtained. The population in the 6P3/2 level obtained from the saturation measurements was also determined by the absorption measurement of narrow spectral line from a Cs hollow cathode lamp. The agreement between the results obtained in these two ways is very good. It was shown that 5% of the ground state population could be transferred to the first excited state by pumping the Doppler broadened line with a single-mode narrow-band laser. The argon caused line broadening and therefore increased the effective pumping rate in the first excitation step. The dependence of the 852 nm line fluorescence intensity was plotted against the population in the 6P3/2 level determined from the saturation absorption. This can serve as confirmation of the reliability of the method used for the determination of the excited state population.