Population Loss in Closed Optical Transitions οf Rb and Cs Atoms Confined in Micrometric Thin Cells

We present the first experimental observation of narrow dips in the fluorescence profiles of completely closed hyperfine transitions in Rb vapor at high atomic density, which is attributed to the depolarization of the excited state. Moreover, at low atomic density, a narrow peak on the top of the fluorescence profile is demonstrated, centered at the completely closed transition within the $D_{2}$ line of Cs. Experiments are performed in thin (700 μm) alkali cell by single light beam spectroscopy. The cell is filled with Cs containing a small portion of Rb.