Acoustic-vortex generation through orbital angular momentum transfer

We explore the phenomenon of orbital angular momentum (OAM) transfer within a high-quality single-crystal diamond mechanical resonator containing nitrogen-vacancy (NV) centers. By employing a weak acoustic field in conjunction with two microwave fields, we establish a three-level closed-loop system within the spin-triplet ground states $3A$ of the NV center. Analytical findings illuminate the potential for OAM transfer to take place, originating from Laguerre-Gaussian microwave fields and extending to the input acoustic field, consequently engendering an acoustic vortex. In this context, the initial weak microwave probe field is presumed to possess OAM content, and the transference of OAM to the input acoustic field is meticulously examined through the mechanism of three-wave mixing under the condition of multiphoton resonance. We extend our investigation to encompass a composite acoustic vortex, accounting for nonzero radial indices and topological charges attributed to both microwave fields. The outcomes of this paper bear significance as they hold the promise of refining the precision of acoustic sensors deployed in applications encompassing sonar systems, nondestructive testing, medical procedures, medical imaging, and synchronized acoustical tweezers.