Light self-trapping in a large cloud of cold atoms

TL;DR

This paper demonstrates that a large cloud of cold rubidium atoms can act as a saturable Kerr medium, enabling self-trapping of light through self-focusing or defocusing effects depending on laser detuning, supported by experimental and numerical analysis.

Contribution

It introduces the observation of light self-trapping in a cold atom cloud and models it using a simple 2-level atom framework.

Findings

Self-trapping observed in cold atom cloud.

Self-focusing or defocusing depends on laser detuning.

Numerical simulations agree with experimental results.

Abstract

We show that, for a near-resonant propagating beam, a large cloud of cold 87Rb atoms acts as a saturable Kerr medium and produces self-trapping of light. By side fluorescence imaging we monitor the transverse size of the beam and, depending on the sign of the laser detuning with respect to the atomic transition, we observe self-focusing or -defocusing, with the waist remaining stationary for an appropriate choice of parameters. We analyze our observations by using numerical simulations based on a simple 2-level atom model.