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Longitudinal orbital angular momentum (OAM) is a fundamental property of light that has been the subject of extensive research and applied to diverse important applications, such as optical tweezers, super-resolution imaging, and optical information processing. Recently, photons have been observed to possess transverse OAM, where the OAM vector is orthogonal to the direction of light propagation. As the carrier for this unique OAM, the spatiotemporal (ST) optical vortex has attracted considerable interest. Here, we provide a general overview of recent experimental and theoretical advances on such vortices, presenting their synthesis and measurement strategies, highlighting their nontrivial properties in linear propagation and interaction with nonlinear matter, and discussing the possible future trends and challenges.
Chen et al. (Wed,) studied this question.