Polychromatic forward-directed sub-Doppler emission from sodium vapour

TL;DR

This paper investigates the mechanisms of ultraviolet to mid-infrared light generation in sodium vapour via two-photon excitation and four-wave mixing, highlighting the role of orbital angular momentum transfer for applications like detection and laser guide stars.

Contribution

It elucidates the orbital angular momentum transfer process in sodium vapour's four-wave mixing, revealing the spectral linewidth and mechanisms of new-field generation under continuous-wave excitation.

Findings

Spectral linewidth of 9.5 MHz at 819.7 nm in four-wave mixing

Upper linewidth limit for generated fields at 2338 nm and 9093 nm

Insights into light generation mechanisms relevant for detection and laser guide stars

Abstract

The mechanisms responsible for ultraviolet to mid-infrared light generation in sodium vapours two-photon excited with continuous-wave sub-100 mW power resonant laser radiation are elucidated from orbital angular momentum transfer of the applied light to the generated fields. The measured 9.5 MHz-wide spectral linewidth of the light at 819.7 nm generated by four-wave mixing, sets an upper limit to the linewidth of two fields resulting from amplified spontaneous emission at 2338 nm and 9093 nm on population inverted transitions. Understanding details of this new-field generation is central to applications such as stand-off detection and directional laser guide stars.