Light interacting with atomic ensembles: collective, cooperative and mesoscopic effects

TL;DR

This paper reviews collective light scattering effects in atomic ensembles, explaining their dependence on density and optical depth, and linking quantum optics with mesoscopic physics through theoretical models and experimental insights.

Contribution

It provides a broad perspective on cooperative scattering, clarifies the roles of density and optical depth, and connects concepts across quantum optics and mesoscopic physics.

Findings

Decay of fluorescence depends on optical depth in dilute samples

Incoherent multiple scattering can saturate fluorescence

Weak localization affects diffusion coefficient and susceptibility

Abstract

Cooperative scattering has been the subject of intense research in the last years. In this article, we discuss the concept of cooperative scattering from a broad perspective. We briefly review the various collective effects that occur when light interacts with an ensemble of atoms. We show that some effects that have been recently discussed in the context of 'single-photon superradiance', or cooperative scattering in the linear-optics regime, can also be explained by 'standard optics', i.e., using macroscopic quantities such as the susceptibility or the diffusion coefficient. We explain why some collective effects depend on the atomic density, and others on the optical depth. In particular, we show that, for a large and dilute atomic sample driven by a far-detuned laser, the decay of the fluorescence, which exhibits superradiant and subradiant dynamics, depends only on the on-resonance optical depth. We also discuss the link between concepts that are independently studied in the quantum-optics community and in the mesoscopic-physics community. We show that the coupled-dipole model predicts a departure from Ohm's law for the diffuse light, that incoherent multiple scattering can induce a saturation of fluorescence and we also show the similarity between the weak-localization correction to the diffusion coefficient and the inaccuracy of Lorentz local field correction to the susceptibility.