Coherent Inelastic Backscattering of Intense Laser Light by Cold Atoms

We present a nonperturbative treatment of coherent backscattering of intense laser light from cold atoms and predict a nonvanishing backscattering signal even at very large intensities, due to the constructive (self-)interference of inelastically scattered photons.

Figure 1

Elementary configuration for coherent backscattering (CBS) of intense light (thick arrows) by two isotropic dipolar transitions in the helicity preserving polarization channel (dashed arrows). The sublevels $|1⟩$ and $|3⟩$ of both atoms have magnetic quantum number $m=0$; sublevels $|2⟩$ and $|4⟩$ correspond to $m=-1$ and $m=1$, respectively.

Figure 2

Total intensities of the ladder, the crossed terms, and their sum $I_{\mathrm{s}\mathrm{s}}^{\mathrm{t}\mathrm{o}\mathrm{t}[2]}$, in the helicity preserving channel, as functions of the saturation parameter $s$ at resonance, $\Delta =0$.

Figure 3

Enhancement factor $\alpha$ in the helicity preserving channel versus saturation parameter $s$. Solid curve, on resonance ($\Delta =0$); dashed curve, off resonance ($\Delta =\gamma$). Straight lines represent the perturbative prediction $2-(1+\delta )s/4$ of 10. Inset: The finite enhancement ${\alpha }_{\infty }\simeq 1.09$ signals residual photon (self-)interference, even in the deep inelastic regime.