Spatiotemporal torquing of light

TL;DR

This paper demonstrates the controlled transfer of transverse orbital angular momentum to light pulses through rapid phase perturbations or energy removal, expanding understanding of light-matter interactions with spatiotemporal vortex structures.

Contribution

It introduces a novel method for imparting transverse OAM to short light pulses via fast transient phase changes or energy extraction, supported by a new theoretical framework.

Findings

Transverse OAM can be transferred only with rapid phase perturbations or energy removal.

The developed theory accurately predicts the light-matter interaction in these scenarios.

First measurement of spatiotemporal optical vortices explained by torque-based theory.

Abstract

We demonstrate the controlled spatiotemporal transfer of transverse orbital angular momentum (OAM) to electromagnetic waves: the spatiotemporal torquing of light. This is a radically different situation than OAM transfer to longitudinal, spatially-defined OAM light by stationary or slowly varying refractive index structures such as phase plates or air turbulence. We show that transverse OAM can be imparted to a short light pulse only for (1) sufficiently fast transient phase perturbations overlapped with the pulse in spacetime, or (2) energy removal from a pulse that already has transverse OAM. Our OAM theory for spatiotemporal optical vortex (STOV) pulses [Phys. Rev. Lett. 127, 193901 (2021)] correctly quantifies the light-matter interaction of this experiment, and provides a torque-based explanation for the first measurement of STOVs [Phys. Rev. X 6, 031037 (2016)].