Spectroscopy in an extremely thin vapor cell: Comparing the cell-length dependence in fluorescence and in absorption techniques

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/lambda, with L the cell thickness (Lsimilar to150-1800 nm) and lambda the wavelength of the Rb D-2 line (lambda=780 mn). The Dicke-type coherent narrowing [ G. Dutier , 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+1)lambda/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=nlambda.