Fluid description of the cooperative scattering of light by spherical atomic clouds

TL;DR

This paper develops a fluid model to describe cooperative light scattering in spherical cold atomic clouds, deriving solutions for various density profiles and analyzing Mie resonances' effects on scattering properties.

Contribution

It introduces a new fluid-based solution for light scattering in spherical atomic clouds with arbitrary density profiles, including infinite boundary cases.

Findings

Mie resonances act as cavity modes within atomic clouds.

Resonances influence scattered intensity and radiation pressure.

Tuning laser frequency or atom number reveals resonance effects.

Abstract

When a cold atomic gas is illuminated by a quasi-resonant laser beam, light-induced dipole-dipole correlations make the scattering of light a cooperative process. Once a fluid description is adopted for the atoms, many scattering properties are captured by the definition of a complex refractive index. The solution of the scattering problem is here presented for spherical atomic clouds of arbitrary density profiles, such as parabolic densities characteristic of ultra-cold clouds. A new solution for clouds with infinite boundaries is derived, that is particularly useful for the Gaussian densities of thermal atomic clouds. The presence of Mie resonances, a signature of the cloud acting as a cavity for the light, is discussed. These resonances leave their fingerprint in various observables such as the scattered intensity or in the radiation pressure force, and can be observed by tuning the frequency of the incident laser field or the atom number.