Saturated absorption spectroscopy: elimination of crossover resonances with the use of a nanocell

It is demonstrated that the velocity-selective optical pumping/saturation resonances of the reduced absorption in a Rb vapor nanocell with thickness L = λ, 2λ, and 3λ (resonant wavelength λ = 780 nm) allow for the complete elimination of crossover (CO) resonances. We observe well-pronounced resonances corresponding to the F g = 3 → F e = 2, 3, and 4 hyperfine transitions of the 85Rb D 2 line with line widths close to the natural width. A small CO resonance located midway between F g = 3 → F e = 3 and F g = 3 → F e = 4 transitions appears only for L 4λ. The D2 line (λ = 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 μm. The absence of the CO resonances for nanocells with L λ is attractive for the frequency reference application and for studying the transitions between the Zeeman sublevels in external magnetic fields. © 2008 Pleiades Publishing, Ltd.