Fluorescence Spectroscopy Of Excited Alkali Atoms By Laser Resonant Exciation

The collisional energy transfer process Rb(5 PJ )+ M under gas cell conditions has been investigated, where M is He, N2. The Rb (5 P3 /2)state was excited by a diode laser. And applying the CW laser absorption and fluorescence method, the cross sections for the fine structure mixing and quenching of the Cs(6P) state, induced by collision with N2 molecules, have been measured.(1) The direct fluorescence and the sensitized fluorescence as a function of quenching gas pressure had been measured. For quenching by He where only electronic to translational energy transfer is possible. However, in the N2 case, electronics to vibrational or rotational transfer is important. Using a two-state rate equation model, the transfer rate coefficients from Rb(5 PJ ) had been obtained. The rate coefficient ( k 2H1e) for 5 P3 2→5P12 transfer in collision with He is 2.61×10-12 cm3s-1. By comparing the direct and sensitized fluorescence intensities for He and N2 case, and fitting the experimental results to the rate equation analysis, we estimate that the rate coefficient (2k 2N1) for 5 P3 2→5P1 2transfer in collision with N2 is 1.38×10-12 cm3s-1. The quenching rate coefficient (k N2) out of the 5PJ state is 5.23×10-12 cm3s-1.We find that the rate coefficient k N2 is∽4 times larger than the 2k 2N1. The assumption that the Cs-N2 energy transfer occurs primarily in collinear collision geometry is supported.(2) Cesium atoms are optically excited to the 6P3/2 state. The excited atom density and spatial distribution are mapped by monitoring the absorption of a counterpro- pagating single mode laser beam that tuned to the 6PJ→8S1/2 transitions. The effective radiative rates are calculated for the 6PJ→6S transitions. The fluorescence intensity I895 of the sensitized 6P1/2→6S1/2 emission is measured as a function of N2 density in the range 2×10163/2→1/2 = (0.42±0.17)×10^-16cm² andσ_D= (1.31±0.52)×10^-16cm² for the 6PJ fine-structure mixing and quenching, respectively, due to collision with N2 molecules. Our values for these cross sections are in agreement, within combined error bars, with values we have recently obtained under different experimental conditions.