Observation of OAM sidebands due to optical reflection

TL;DR

This paper studies how the orbital angular momentum of a light beam changes upon reflection, revealing significant OAM sidebands caused by beam spread, supported by a new theoretical model and experimental validation.

Contribution

It introduces a spatial Fresnel coefficient theory to predict OAM sidebands during reflection, validated through experiments.

Findings

OAM sidebands are significant even for modest beam spreads

Theoretical predictions match experimental results

Angular spread influences OAM during reflection

Abstract

We investigate how the orbital angular momentum (OAM) of a paraxial light beam is affected upon reflection at a planar interface. Theoretically, the unavoidable angular spread of the (paraxial) beam leads to OAM sidebands which are found to be already significant for modest beam spread (0.05). In analogy to the polarization Fresnel coefficients we develop a theory based upon spatial Fresnel coefficients; this allows straightforward prediction of the strength of the sidebands. We confirm this by experiment.