Frequency-comb-induced radiation pressure force in dense atomic clouds

We investigate the frequency comb induced radiation pressure force acting on a cloud of cold $^{87}$Rb atoms. Reduction and spectral broadening of the frequency comb force are observed as the cloud's optical thickness is increased. Since the radiation pressure force is uniquely determined by light scattered by an atomic cloud, we discuss different scattering mechanisms, and point to the shadow effect as the dominant mechanism affecting FC-induced force in resonantly excited dense atomic clouds. Our results improve the understanding of the interaction of frequency comb light with many-atom ensembles, which is essential for novel frequency comb applications in simultaneous multi-species cooling, multi-mode quantum memories, and multi-mode atom-light interfaces.