We compare the behavior of absorption and of resonance fluorescence spectra in an extremely thin Rb vapor cell as a function of the ratio of L / , with L the cell thickness ͑L ϳ 150-1800 nm͒ and the wavelength of the Rb D 2 line ͑ = 780 mn͒. The Dicke-type coherent narrowing [G. Dutier et al., Europhys. Lett. 63, 35 (2003)] is observed only in transmission measurements, in the linear regime, with its typical collapse and revival, which reaches a maximum for L = ͑2n +1͒ /2 (n integer). It is shown not to appear in fluorescence, whose behavior-amplitude, and spectral width, is more monotonic with L. Conversely, at high-intensity, the sub-Doppler saturation effects are shown to be the most visible in transmission around L = n.
Saturation effects affecting absorption and fluorescence spectra of an atomic vapor confined in an Extremely Thin Cell (cell thickness L < 1µm) are investigated experimentally and theoretically. The study is performed on the D2 line (λ = 852nm) of Cs and concentrates on the two situations L = λ/2 and L = λ, the most contrasted ones with respect to the length dependence of the coherent Dicke narrowing. For L = λ/2, the Dicke-narrowed absorption profile simply broadens and saturates in amplitude when increasing the light intensity, while for L = λ, sub-Doppler dips of reduced absorption at line-center appear on the broad absorption profile. For a fluorescence detection at L = λ, saturation induces narrow dips, but only for hyperfine components undergoing a population loss through optical pumping. These experimental results are interpreted with the help of the various existing models, and are compared with numerical calculations based upon a two-level modelling that considers both a closed and an open system.
It is experimentally demonstrated that use of an extremely thin cell (ETC) with the thickness of a Rb atomic vapor column of ϳ400 nm allows one to resolve a large number of individual transitions between Zeeman sublevels of the D 1 line of 87 Rb and 85 Rb in the sub-Doppler fluorescence excitation spectra in an external magnetic field of ϳ200 G. It is revealed that due to the peculiarities of the Zeeman effect for different hyperfine levels of Rb, all allowed transitions between magnetic sublevels can be clearly resolved for 87 Rb F g ϭ 1 → F e ϭ 1, 2 and F g ϭ 2 → F e ϭ 1, 2 fluorescence excitation. Also, relatively good spectral resolution can be achieved for 85 Rb F g ϭ 2 → F e ϭ 2, 3 fluorescence excitation. Some partial resolution of transitions between magnetic sublevels is achieved for 85 Rb F g ϭ 3 → F e ϭ 2, 3 fluorescence excitation. The spectral resolution of individual transitions allows one to easily observe both linear and nonlinear Zeeman effects in the fluorescence excitation spectra obtained with the help of the ETC. In the fluorescence spectra of a cell of usual length there is no evidence of a spectral resolution of individual transitions at B ϳ 200 G. A simple magnetometer based on ETC with Rb with a submicrometer spatial resolution is described.
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