Fluorescence monitoring of laser induced population changes of 6P and 6D levels in cesium vapor

Observations of enhancement and reduction of the fluorescence intensity in the continuous-wave excitation of Cs atomic vapor is reported. The reduction is due to a depopulation of the 6²p_3/2^o state upon illumination of a Cs vapor cell with light corresponding to the 6²P_3/2^o→6²D_5/2 transition (917.23 nm). Collisional relaxation of the 6²D_5/2 atoms to the 6²D_3/2 state, followed by radiative decay to the 6²P_1/2^o state (876.14 nm), creates an increase in the population of the 6²P_1/2^o state. The increase in the excited state population results in an increase in the fluorescence intensity of the 6²P_1/2^o→6²S_1/2 transition (894.35 nm). These laser induced population changes, monitored by the decrease or increase of the corresponding fluorescence signals, were modeled using a simplified density matrix formalism, which allowed an order of magnitude estimate of the rates of level mixing between 6²D states and 6²P states.