Twisted Light and the mirage effect

TL;DR

This paper investigates how a beam carrying orbital angular momentum (OAM) transforms when passing through a water-ethanol column with a refractive index gradient, revealing mirror inversion and topological charge changes.

Contribution

It demonstrates the smooth mirror inversion of OAM beams in a gradient index medium and explores the resulting complex topological and astigmatic transformations.

Findings

Mirror inversion occurs smoothly in gradient index media.

Topological charge can be inverted or partially inverted.

Beam exhibits astigmatic changes during inversion.

Abstract

We study the transformation of an OAM-carrying beam propagating through a vertical gradient of refractive index present in a water-ethanol column. Proper liquid mixing and incidence conditions upon the solution cause the beam to undergo a mirror inversion along the vertical direction, forming an inferior mirage. This path reverses the handedness of the beam and unlike mirror inversion witnessed at sharp interfaces, mirror inversion occurs smoothly and topological charge inversion is accompanied by astigmatic changes. It is also possible to obtain, at the exit of the solution, a beam that has been partially inverted, thus presents spatially varying orbital fluxes.