Transverse orbital angular momentum of spatiotemporal optical vortices: setting the record straight

The nature of the transverse orbital angular momentum (tOAM) associated with spatiotemporal optical vortex (STOV) pulses has been the subject of recent debate. We demonstrate that the approaches to tOAM presented in several recent papers are incorrect and lead to unphysical results, including erroneous claims of zero total tOAM for a freely propagating STOV pulse. We emphasize the importance of calculating the OAM of any extended physical object at a common instant of time, and reemphasize the special status of the center of energy as a reference point for all OAM calculations. The theory presented in [Phys. Rev. Lett.127, 193901 (2021)10.1103/PhysRevLett.127.193901] is the only correct classical field-based framework that both agrees with experiments and provides a self-consistent understanding of transverse OAM in spatiotemporal light fields.