Monday, October 16th, 11h30, Room 454 A, Condorcet Building.

The momentum of sound waves and how it can be exchanged with matter

Diego Baresch

Département d’Acoustique Physique

I2M (Institut de Mécanique et d’Ingénierie)

CNRS, UMR 5295
Université de Bordeaux, France

Abstract: Sound waves, just like light, can carry a momentum characteristic of any field in translational motion through space. Its manifestation becomes clear when sound interacts with an interface, either through absorption or scattering processes, and generates an average pressure that is applied on it, termed acoustic radiation pressure. More generally it can be shown that acoustic waves generate an average radiation stress, resulting in a net radiation force and torque exerted on matter. We have exploited this action to develop single-beam acoustical tweezers [1], an experimental tool that is similar in principle to its optical counterpart and exhibits interesting characteristics for the contactless manipulation and mechanical characterization of biological systems or complex interfaces. From a more fundamental perspective, we are currently testing recent propositions on the existence of orbital and spin angular momentum components in sound waves, the latter being hitherto thought only relevant in the context of circularly polarized electromagnetic waves [2,3].

[1] D. Baresch, J.-L. Thomas and R. Marchiano, “Observation of a single-beam gradient force acoustical trap for elastic particles: acoustical tweezers”, Physical Review Letters, 2016.

[2] D. Baresch, J.-L. Thomas and R. Marchiano, “Orbital angular momentum transfer to stably trapped elastic particles in acoustic vortex beams”, Physical Review Letters, 2018.

[3] L. Alhaïtz et al, “Confined phase singularities reveal the spin-to-orbital angular momentum conversion of sound waves”, Physical Review Letters, 2023.

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