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

Abstract

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 $L∕\ensuremath{\lambda}$, with $L$ the cell thickness $(L\ensuremath{\sim}150--1800\phantom{\rule{0.3em}{0ex}}\mathrm{nm})$ and $\ensuremath{\lambda}$ the wavelength of the Rb ${D}_{2}$ line $(\ensuremath{\lambda}=780\phantom{\rule{0.3em}{0ex}}\mathrm{mn})$. 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 $L=(2n+1)\ensuremath{\lambda}∕2$ ($n$ 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 $L=n\ensuremath{\lambda}$.