Coherent Scattering of Near-Resonant Light by a Dense, Microscopic Cloud of Cold Two-Level Atoms: Experiment versus Theory

TL;DR

This study experimentally measures and compares the coherent scattering of near-resonant light by cold atomic clouds with theoretical models, revealing good agreement at low densities but discrepancies at higher densities, highlighting ongoing challenges in understanding dense atomic media.

Contribution

The paper provides experimental data on coherent scattering in dense cold atomic clouds and validates the Maxwell-Bloch model at low densities, while identifying limitations at higher densities.

Findings

Models agree well at low densities ($n/k^3 extless 0.1$)

Deviations between models and data increase at higher densities

Light scattering in dense ensembles remains not fully understood

Abstract

We measure the coherent scattering of low-intensity, near-resonant light by a cloud of laser-cooled two-level rubidium atoms with a size comparable to the wavelength of light. We isolate a two-level atomic structure by applying a 300G magnetic field. We measure both the temporal and the steady-state coherent optical response of the cloud for various detunings of the laser and for atom numbers ranging from 5 to 100. We compare our results to a microscopic coupled-dipole model and to a multi-mode, paraxial Maxwell-Bloch model. In the low-intensity regime, both models are in excellent agreement, thus validating the Maxwell-Bloch model. Comparing to the data, the models are found in very good agreement for relatively low densities ($n/k^3\lesssim 0.1$), while significant deviations start to occur at higher density. This disagreement indicates that light scattering in dense, cold atomic ensembles is still not quantitatively understood, even in pristine experimental conditions.