Arithmetic with optical topological charged in step-wise excited Rb vapour

TL;DR

This paper experimentally demonstrates the transfer, addition, and subtraction of orbital angular momentum in four-wave mixing within Rb vapor, showing that blue light coherently inherits the total OAM of the input laser fields across various conditions.

Contribution

It provides new experimental evidence of OAM conservation and transfer in nonlinear wave mixing in Rb vapor, including non-collinear geometries and different optical topological charges.

Findings

OAM is conserved during four-wave mixing in Rb vapor.

Blue light accumulates the total OAM of the input laser beams.

Spectral and power dependencies of vortex and plane wave front blue light are characterized.

Abstract

We report on experimentally observed addition, subtraction and cancellation of orbital angular momentum (OAM) in the process of parametric four-wave mixing that results in frequency up- and down-converted emission in Rb vapour. Specific features of OAM transfer from resonant laser fields with different optical topological charges to the spatially and temporally coherent blue light have been considered. We have observed the conservation of OAM in nonlinear wave mixing in a wide range of experimental conditions including a non-collinear geometry of the applied laser beams and furthermore that the coherent blue light accumulates the total orbital angular momentum of the applied laser light. Spectral and power dependences of vortex and plane wave front blue light beams have been compared.