Peculiarities of Fluorescence of Rb Atomic Vapors Contained in a cell with an anti-relaxation coating

The features of the fluorescence spectra of Rb D$_1$-line vapors were studied for the first time using a cell with anti-relaxation PolyDiMethylSiloxane (PDMS) coating. At high intensities ($>$ 200 mW/cm$^2$) of a cw narrow-band diode laser in the transmission spectra due to the effect of optical pumping, there are no absorption lines at atomic transitions, while in the fluorescence spectrum, all 8 atomic transitions of the D$_1$ line are pronounced. A strong redistribution of fluorescence intensity is registered for atomic transitions of $^{85}$Rb and $^{87}$Rb: in particular, the ratio of fluorescence amplitudes for transitions of $^{87}$Rb $F_g =1\to F_e$ = 1, 2 in a regular cell is 5, while for a PDMS cell it is equal to 1.5. A physical explanation of the observed features of fluorescence in a PDMS cell is given. A significant increase of fluorescence intensity and a change in redistribution at the transitions with increasing of the PDMS cell temperature is demonstrated. It is noted that at large intensities of laser radiation (when there are no peaks on the transmission/absorption spectra of atomic transitions), fluorescence spectra remain the only convenient and informative tool for studying the behavior of atoms.