Spatiotemporal orbital angular momentum (ST-OAM) of light is an emergent, spatiotemporally sculptured light. Such spatiotemporal optical vortices carry transverse OAM and exhibit novel properties. However, the lack of a simple and straightforward characterization method substantially slows its progress and potential adaptions for future applications. Here we demonstrated a simple, stationary, single-frame method to quantitatively characterize ST-OAM pulses. Our new method can measure the presence of ST-OAM, space-time topological charge numbers, OAM helicity, pulse dispersion, and beam divergence. We also investigated the nonlinear properties of ST-OAM pulses, uncovering the conservation of space-time topological charges in a second-harmonic generation process.
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