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Orbital angular momentum of spatiotemporal vortices: A ray-mechanical analogy

Sophie Vo1, Konstantin Y. Bliokh2,3, and Miguel A. Alonso4,1

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Phys. Rev. A 114, 013508 – Published 9 July, 2026

DOI: https://doi.org/10.1103/hvqp-p3kl

Abstract

Spatiotemporal vortex pulses (STVPs) are wavepackets that carry transverse orbital angular momentum (OAM) whose proper quantification has been the subject of recent debate. In this work, we introduce a simplified mechanical model of STVPs, consisting of a loop of noninteracting point particles traveling at a uniform constant speed but at slightly different angles. We examine different initial conditions for the particle loop, including configurations that are elliptic in space at a given time and configurations that are elliptic in spacetime at a fixed propagation distance. Furthermore, by employing a nonuniform mass distribution, the particle loop can mimic an STVP not only in configuration space, but also in momentum space. Remarkably, when supplemented by a semiclassical vorticity quantization condition, our mechanical model exactly reproduces different wave-based OAM results previously reported for paraxial STVPs.

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Phys. Rev. A 114, 013508– Published 9 July, 2026
  • Received 3 January 2026
  • Accepted 20 May 2026
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