Acoustic pressure wave orientation determination using structured light

Acoustic waves propagate through matter in various states of aggregation and have proven to be a useful tool for numerous applications, from biology to industrial engineering. Their temporal and spatial information content reflects their generation processes and propagation, making them very valuable for sensor technologies and diagnostics. These waves cause small changes in the refractive index of materials, which can be easily measured using optical detection methods. We demonstrate an approach for spatial and temporal measurements that can determine the two-dimensional directionality of an acoustic pulse relative to the optical axis of a phase and amplitude structured probe beam. Our scheme directly measures the temporal power variance between the components of a superposition of orbital angular momentum modes, where the direction of the acoustic wave can be determined through sequentially varying the relative phase between the modes within the superposition. We expect our results could inspire the use of bespoke structured fields for the mapping of acoustic pressure-wave trajectories.