Saturation-induced coherence loss in coherent backscattering of light

We use coherent backscattering of light by cold strontium atoms to study phase-breaking mechanisms in the multiple-scattering regime. As the probe light intensity is increased, the atomic optical transition starts to be saturated. Nonlinearities and inelastic scattering then occur. The latter induces a characteristic phase-breaking time that reduces the wave coherence. In our experiment, this leads to a strong reduction of the enhancement factor of the coherent backscattering cone. The results at different probe detuning are also presented.

Figure 1

Resonant ($\delta =0$) coherent transmission $T$ along a diameter of the cold strontium cloud as a function of the saturation parameter $s$. The solid line corresponds to the theoretical Lambert-Beer prediction taking into account the nonlinear reduction of the scattering cross section. There is good agreement with the experimental data up to $s=1.2$.

Figure 2

Resonant ($\delta =0$) CBS enhancement factor as a function of the incident saturation parameter $s$. The coherent transmission value is kept fixed to $T=0.085$.

Figure 3

Off-resonant ($\delta =\Gamma ∕2$) CBS enhancement factor as a function of the incident saturation parameter $s$. The coherent transmission value is kept fixed to $T=0.19$. Compared to the resonant case, the overall behavior is different with a stronger decrease at low $s$.