Observation of a Cooperative Radiation Force in the Presence of Disorder

TL;DR

This paper reports the first experimental observation of reduced radiation force due to cooperative scattering in cold atomic clouds, demonstrating how disorder influences collective light-matter interactions.

Contribution

It provides experimental evidence of cooperative radiation force effects in atomic ensembles and introduces an analytical model bridging disorder and cooperativity regimes.

Findings

Radiation force is reduced in cooperative scattering regimes.

Disorder suppresses cooperativity in light scattering.

Experimental results agree with the analytical model.

Abstract

Cooperative scattering of light by an extended object such as an atomic ensemble or a dielectric sphere is fundamentally different from scattering from many point-like scatterers such as single atoms. Homogeneous distributions tend to scatter cooperatively, whereas fluctuations of the density distribution increase the disorder and suppress cooperativity. In an atomic cloud, the amount of disorder can be tuned via the optical thickness, and its role can be studied via the radiation force exerted by the light on the atomic cloud. Monitoring cold $^{87}\text{Rb}$ atoms released from a magneto-optical trap, we present the first experimental signatures of radiation force reduction due to cooperative scattering. The results are in agreement with an analytical expression interpolating between the disorder and the cooperativity-dominated regimes.