Observation of acoustic spatiotemporal vortices

TL;DR

This paper reports the first creation of acoustic spatiotemporal vortex pulses using an acoustic meta-grating, revealing topological phase transitions and demonstrating robustness against structural perturbations, opening new avenues in wave physics.

Contribution

It introduces a novel method to generate acoustic spatiotemporal vortices and uncovers their topological properties and robustness, advancing wave manipulation techniques.

Findings

First generation of acoustic spatiotemporal vortex pulses

Observation of topological phase transitions in transmission spectra

Vortices exhibit robustness against structural perturbations

Abstract

Vortices in fluids and gases have piqued the interest of human for centuries. Development of classical-wave physics and quantum mechanics highlighted wave vortices characterized by phase singularities and topological charges. In particular, vortex beams have found numerous applications in modern optics and other areas. Recently, optical spatiotemporal vortex states exhibiting the phase singularity both in space and time have been reported. Here, we report the first generation of acoustic spatiotemporal vortex pulses. We utilize an acoustic meta-grating with mirror-symmetry breaking as the spatiotemporal vortex generator. In the momentum-frequency domain, we unravel that the transmission spectrum functions exhibit a topological phase transition where the vortices with opposite topological charges are created or annihilated in pairs. Furthermore, with the topological textures of the nodal lines, these vortices are robust and exploited to generate spatiotemporal vortex pulse against structural perturbations and disorder. Our work paves the way for studies and applications of spatiotemporal structured waves in acoustics and other wave systems.