Narrow band amplification of light carrying orbital angular momentum

TL;DR

This paper demonstrates narrow-band amplification of light carrying orbital angular momentum using Raman gain in cold cesium atoms, preserving the vortex phase structure with high spectral selectivity.

Contribution

It introduces a method for amplifying vortex beams via narrow Raman gain in cold atoms, maintaining phase integrity and achieving significant gain within a narrow spectral width.

Findings

Achieved 20% single-pass Raman gain of vortex light.

Spectral width of gain is approximately 1 MHz, much narrower than natural linewidth.

The process preserves the phase structure of the vortex beam.

Abstract

We report on the amplification of an optical vortex beam carrying orbital angular momentum via induced narrow Raman gain in an ensemble of cold cesium atoms. A 20\% single-pass Raman gain of a weak vortex signal field is observed with a spectral width of order of 1 MHz, much smaller than the natural width, demonstrating that the amplification process preserves the phase structure of the vortex beam. The gain is observed in the degenerated two-level system associated with the hyperfine transition $6S_{1/2}(F=3)\leftrightarrow 6P_{3/2}(F^{\prime}=2)$ of cesium. Our experimental observations are explained with a simple theoretical model based on a three-level $\Lambda$ system interacting coherently with the weak Laguerre-Gauss field and a strong coupling field, including an incoherent pumping rate between the two degenerate ground-states.