On the Coupling of Photon Spin to Electron Orbital Angular Momentum

TL;DR

This paper demonstrates the transfer of photon spin to electron orbital angular momentum in specially designed structures, resulting in measurable photovoltages, and interprets these effects through a classical electrodynamic model of photons.

Contribution

It provides experimental evidence of photon spin transfer to electrons and offers a new classical electrodynamic interpretation of optical spin effects.

Findings

Measured photovoltages up to 0.2 microvolts depending on polarization.

Results align with a classical electrodynamic photon model.

Links to optical spin Hall effect and Fedorov Imbert shift.

Abstract

Partially gold coated 90 degree glass wedges and a semi - infinite slit in a thin film of gold ending in a conducting nano-junction serve as samples to investigate the transfer of photon spin to electron orbital angular momentum. These structures were specifically designed as samples where an incident beam of light is retroreflected. Since in the process of retroreflection the turning sense of a circularly polarized beam of light does not change and the direction of propagation is inverted, the photon spin is inverted. Due to conservation of angular momentum a transfer of photon spin to electron orbital angular momentum of conduction electrons occurs. In the structures a circular movement of electrons is blocked and therefore the transfered spin can be detected as a photovoltage due to an electromotive force which is induced by the transfer of angular momentum. Depending on the polarization of the incident beam, a maximum photovoltage of about 0,2 micro V was measured for both structures. The results are interpreted in terms of a classical electrodynamic model of the monochromatic linearly polarized photon as a propagating solitary electromagnetic wave of finite energy hf which carries an angular momentum h/2pi which is elaborated elsewhere where h is Plancks constant and f the frequency of light. The relative values of the measured photovoltages for different polarizations can well be explained by the electrodynamic model of a photon and an associated spin angular momentum. The absolute values of the measured photovoltages are also consistent with the interpretation. The observed effects are closely related to the lateral Fedorov Imbert shift of focused beams in optics and the optical spin Hall effect and to other non linear optical effects such as the inverse faraday effect for which a new interpretation is given here in terms of the electrodynamic model of the photon and its spin.