Measurement of Optical Orbital and Spin Angular Momentum: Implications for Photon Angular Momentum

TL;DR

This paper investigates the measurement of optical vortex beams' angular momentum, comparing classical and quantum formulations, and explores how experiments could determine the physically accurate description.

Contribution

It analyzes the differences between classical and quantum expressions for optical angular momentum and proposes optical measurements to distinguish between them.

Findings

Classical and quantum formulas for spin angular momentum differ significantly.

Optical measurements could potentially identify the correct physical description.

Implications for understanding photon angular momentum in optical systems.

Abstract

The expression for the total angular momentum carried by a laser optical vortex beam, splits, in the paraxial approximation, into two terms which seem to represent orbital and spin angular momentum respectively. There are, however, two very different competing versions of the formula for the spin angular momentum, one based on the use of the Poynting vector, as in classical electrodynamics, the other related to the canonical expression for the angular momentum which occurs in Quantum Electrodynamic. I analyze the possibility that a sufficiently sensitive optical measurement could decide which of these corresponds to the actual physical angular momentum carried by the beam.