Threshold of a random laser based on Raman gain in cold atoms

TL;DR

This paper proposes a method to determine the threshold of a cold-atom-based random laser using spectroscopic measurements of atomic polarizability, and experimentally evaluates the threshold for Raman gain in cold atoms.

Contribution

It introduces a spectroscopic approach to predict the random laser threshold in cold atoms and experimentally estimates this threshold for Raman gain between Zeeman states.

Findings

Critical optical thickness around 200 for lasing threshold

Threshold can be predicted from atomic polarizability measurements

Experimental feasibility within current cold-atom setups

Abstract

We address the problem of achieving a random laser with a cloud of cold atoms, in which gain and scattering are provided by the same atoms. In this system, the elastic scattering cross-section is related to the complex atomic polarizability. As a consequence, the random laser threshold is expressed as a function of this polarizability, which can be fully determined by spectroscopic measurements. We apply this idea to experimentally evaluate the threshold of a random laser based on Raman gain between non-degenerate Zeeman states and find a critical optical thickness on the order of 200, which is within reach of state-of-the-art cold-atom experiments.