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

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.