Observation of cooperative Mie scattering from an ultracold atomic cloud

TL;DR

This study investigates how cooperative Mie scattering influences light scattering from ultracold atomic clouds, revealing the roles of superradiance and Mie effects in radiation pressure modifications.

Contribution

It provides experimental insights into the interplay between superradiant scattering and Mie scattering in ultracold atomic ensembles, clarifying their impact on radiation pressure.

Findings

Maximum radiation pressure observed at a specific phase shift.

Identification of the transition from Rayleigh-Debye-Gans to Mie scattering regimes.

Demonstration of suppression and enhancement of scattering due to cooperativity.

Abstract

Scattering of light at a distribution of scatterers is an intrinsically cooperative process, which means that the scattering rate and the angular distribution of the scattered light are essentially governed by bulk properties of the distribution, such as its size, shape, and density, although local disorder and density fluctuations may have an important impact on the cooperativity. Via measurements of the radiation pressure exerted by a far-detuned laser beam on a very small and dense cloud of ultracold atoms, we are able to identify the respective roles of superradiant acceleration of the scattering rate and of Mie scattering in the cooperative process. They lead respectively to a suppression or an enhancement of the radiation pressure. We observe a maximum in the radiation pressure as a function of the induced phase shift, marking the borderline of the validity of the Rayleigh-Debye-Gans approximation from a regime, where Mie scattering is more complex. Our observations thus help to clarify the intricate relationship between Rayleigh scattering of light at a coarse-grained ensemble of individual scatterers and Mie scattering at the bulk density distribution.