The Angular Momentum of Topologically Structured Darkness

TL;DR

This paper investigates the angular momentum properties of topologically structured darkness in fractional vortex beams, combining theoretical analysis and experimental measurement to reveal the roles of evanescent waves and intrinsic/extrinsic angular momentum components.

Contribution

It provides the first direct measurement of intrinsic orbital angular momentum in light with both intrinsic and extrinsic components, and explains discrepancies in total angular momentum of fractional vortices.

Findings

Structured darkness's extrinsic angular momentum is linked to evanescent waves.

First direct measurement of intrinsic orbital angular momentum in complex light fields.

Total angular momentum of fractional vortices does not equal their phase winding number.

Abstract

We theoretically analyze and experimentally measure the extrinsic angular momentum contribution of topologically structured darkness found within fractional vortex beams, and show that this structured darkness can be explained by evanescent waves at phase discontinuities in the generating optic. We also demonstrate the first direct measurement of the intrinsic orbital angular momentum of light with both intrinsic and extrinsic angular momentum, and explain why the total orbital angular momenta of fractional vortices do not match the winding number of their generating phases.