The photonic wheel: demonstration of a state of light with purely transverse angular momentum

TL;DR

This paper demonstrates a novel state of light with purely transverse angular momentum, expanding the understanding of photon angular momentum and enabling new applications in optical manipulation.

Contribution

It introduces and experimentally demonstrates a new state of light with purely transverse angular momentum, previously thought impossible for photons.

Findings

Experimental verification of transverse angular momentum in light

Potential applications in optical tweezers and manipulation

Extension of angular momentum concepts in photonics

Abstract

The concept of angular momentum is ubiquitous to many areas of physics. In classical mechanics, a system may possess an angular momentum which can be either transverse (e.g., in a spinning wheel) or longitudinal (e.g., for a fluidic vortex) to the direction of motion. Photons, however, are well-known to exhibit intrinsic angular momentum which is longitudinal only: the spin angular momentum defining the beam polarization and the orbital angular momentum associated with a spiraling phase front. Here we show that it is possible to generate a novel state of light that contains purely transverse angular momentum, the analogue of a spinning mechanical wheel. We use an optical nano-probing technique to experimentally demonstrate its occurrence in our setup. Such a state of light can provide additional rotational degree of freedom in optical tweezers and optical manipulation.