Spiral bandwidth of four-wave mixing in Rb vapour

TL;DR

This paper investigates how orbital angular momentum is conserved and distributed in four-wave mixing in rubidium vapor, revealing the potential for high-efficiency OAM entanglement across different wavelengths.

Contribution

It experimentally studies the spiral bandwidth of generated light modes in four-wave mixing, demonstrating OAM transfer and entanglement potential in rubidium vapor.

Findings

Small pump OAM is transferred to 420 nm light.

Increasing pump OAM broadens the OAM spectrum of generated light.

Results suggest potential for high-efficiency OAM entanglement across wavelengths.

Abstract

Laguerre-Gauss beams, and more generally the orbital angular momentum of light (OAM) provide valuable research tools for optical manipulation, processing, imaging and communication. Here we explore the high-efficiency frequency conversion of OAM in a four-wave mixing process in rubidium vapour. Conservation of the OAM in the two pump beams determines the total OAM shared by the generated light fields at 420 nm and 5.2 um - but not its distribution between them. We experimentally investigate the spiral bandwidth of the generated light modes as a function of pump OAM. A small pump OAM is transferred almost completely to the 420 nm beam. Increasing the total pump OAM broadens the OAM spectrum of the generated light, indicating OAM entanglement between the generated light fields. This clears the path to high-efficiency OAM entanglement between widely disparate wavelengths.