Linewidth of collimated wavelength-converted emission in Rb vapours

TL;DR

This study measures the spectral linewidth of collimated blue and mid-IR light generated in Rb vapour, showing the linewidth is mainly limited by laser coherence rather than atom-light interaction.

Contribution

It provides the first detailed measurement of the linewidth of collimated mid-IR radiation in Rb vapour, highlighting the influence of laser coherence.

Findings

CBL linewidth is less than 1.3 MHz under various conditions

Linewidth is primarily limited by laser coherence

Upper limit of mid-IR linewidth is several hundred kHz

Abstract

We present a study of the spectral linewidth of collimated blue light (CBL) that results from wave mixing of low-power cw laser radiation at 780 nm and 776 nm and an internally-generated mid-IR field at 5.23 um in Rb vapour. Using a high-finesse Fabry-Perot interferometer the spectral width of the CBL is found to be less than 1.3 MHz for a wide range of experimental conditions. We demonstrate that the CBL linewidth is mainly limited by the temporal coherence of the applied laser fields rather than the atom-light interaction itself. Results obtained with frequency modulated laser light allow an upper limit of several hundred kHz to be set for the linewidth of the collimated mid-IR radiation at 5.23 um, which has not been directly detected.