Coherent scattering of near-resonant light by a Dense Microscopic Cold Atomic cloud

TL;DR

This study investigates how near-resonant light coherently scatters off a dense, cold atomic cloud, revealing complex interactions and deviations from standard models, with implications for understanding light-matter interactions at microscopic scales.

Contribution

It provides experimental measurements and theoretical analysis of coherent scattering in dense atomic clouds, highlighting the importance of dipole-dipole interactions and limitations of mean-field models.

Findings

Observation of resonance shifts, broadening, and saturation effects.

Enhanced dipole-dipole interactions influence scattering behavior.

Discrepancies between mean-field and microscopic models.

Abstract

We measure the coherent scattering of light by a cloud of laser-cooled atoms with a size comparable to the wavelength of light. By interfering a laser beam tuned near an atomic resonance with the field scattered by the atoms we observe a resonance with a red-shift, a broadening, and a saturation of the extinction for increasing atom numbers. We attribute these features to enhanced light-induced dipole-dipole interactions in a cold, dense atomic ensemble that result in a failure of standard predictions such as the "cooperative Lamb shift". The description of the atomic cloud by a mean-field model based on the Lorentz-Lorenz formula that ignores scattering events where light is scattered recurrently by the same atom and by a microscopic discrete dipole model that incorporates these effects lead to progressively closer agreement with the observations, despite remaining differences.