Comment on "Mode Structure and Orbital Angular Momentum of Spatiotemporal Optical Vortex (STOV) Pulses"

TL;DR

This paper clarifies a mathematical error in a previous study on spatiotemporal optical vortices, emphasizing that only the intrinsic transverse orbital angular momentum was correctly evaluated and highlighting issues with the operators used.

Contribution

It identifies a mathematical mistake in prior work and clarifies the correct interpretation of transverse OAM in STOVs, correcting the theoretical understanding.

Findings

The previous evaluation of transverse OAM was only the intrinsic part.

Operators used for OAM evaluation are non-Hermitian, leading to potential complex expectation values.

Correct interpretation of OAM contributions in STOVs is established.

Abstract

We report a mathematical error and a misinterpretation in arXiv:2103.03263v4 [Phys. Rev. Lett. 127, 193901 (2021)] that has led to a debate about the nature of the transverse orbital angular momentum (OAM) of spatiotemporal optical vortices (STOVs). The transverse OAM of STOVs evaluated theoretically in that Letter is actually only the intrinsic contribution, while the operators used to evaluate the intrinsic and extrinsic contributions are not Hermitian operators as they may lead to complex-valued expectation values.