Saturated absorption spectroscopy: elimination of crossover resonances by use of a nanocell

Abstract

It is demonstrated that velocity selective optical pumping/saturation resonances of reduced absorption in a Rb vapor nanocell with thickness \textit{L=} $\hat{I}»$, 2$\hat{I}»$, and 3$\hat{I}»$ (resonant wavelength $\hat{I}»$ = 780 nm) allow the complete elimination of crossover (CO) resonances. We observe well pronounced resonances corresponding to the F${}_g=3$ $\to$ F${}_e=2,3,4$ hyperfine transitions of the ${}^{85}$Rb D${}_2$ line with linewidths close to the natural width. A small CO resonance located midway between F${}_g=3$ $\to$ F${}_e=3$ and F${}_g=3$ $\to$ F${}_e=4$ transitions appears only for \textit{L} = 4$\hat{I}»$. The D${}_2$ line ($\hat{I}»$ = 852 nm) in a Cs nanocell exhibits a similar behavior. From the amplitude ratio of the CO and VSOP resonances it is possible to determine the thickness of the column of alkali vapor in the range of 1 - 1000 $\hat{I}¼$m. The absence of CO resonances for nanocells with $L\sim \hat{I}»$ is attractive for frequency reference application and for studying transitions between Zeeman sublevels in external magnetic fields.

8 pages