Sub-Doppler resonances in the backscattered light from random porous media infused with Rb vapor

We report on the observation of sub-Doppler resonances on the backscattered light from a random porous glass medium with rubidium vapor filling its interstices. The sub-Doppler spectral lines are the consequence of saturated absorption where the incident laser beam saturates the atomic medium and the backscattered light probes it. Some specificities of the observed spectra reflect the transient atomic evolution under confinement inside the pores. Simplicity, robustness, and potential miniaturization are appealing features of this system as a spectroscopic reference.

Figure 1

(a) Scheme of the experimental setup. Only the light scattered towards the photodetector is represented (BS: beam-splitter; PD: photodiode). (b) Backscattered light spectrum for $\theta =0$ around the ${}^{85}$Rb $(F=3\to F^{\prime }=2,3)$ and ${}^{87}$Rb $(F=2\to F^{\prime }=1,2)$ transitions for a $100\mu \text{m}$ porous cell, and (c) for a $10\mu \text{m}$ porous cell.

Figure 2

Typical sub-Doppler resonances derivative recorded for the transition ${}^{85}\text{Rb}(F=3\to F^{\prime }=3)$ and nearby crossover using $6\text{mW}$ light power and $2.0\text{mm}$ beam diameter ($\theta =0$). The peak-to-peak spectral widths are 29 and $32\text{MHz}$ for the cells with mean pore sizes 10 and $100\mu \text{m}$, respectively (integration time constant $300\text{ms}$).

Figure 3

Doppler broadening as a function of the detection angle $\theta$ for the $100\mu \text{m}$ cell (a) and for a $10\mu \text{m}$ cell (b) using a $5\text{mW}$ and $2\text{mm}$ diameter incident beam. (c) Doppler broadening as a function of the angle $\theta$ between the probe ($10\mu \text{W}$, $3.0\text{mm}$ diameter) and pump beam ($500\mu \text{W}$, $3.0\text{mm}$ diameter) in a standard cell (full circles: single transition resonance; open circles: CO resonance; continuous line: linear fit for large angles). (d) Beam configuration considered for saturated absorption spectroscopy.

Figure 4

Power broadening measured for a single transition resonance on the two porous cells as a function of the incident beam power ($\theta \cong 0$, beam diameter: $2\text{mm}$).