Measuring orbital angular momentum of acoustic vortices based on Fraunhofer’s diffraction**Project supported by the National Natural Science Foundation of China (Grant Nos. 61775050 and 11804073), the Natural Science Foundation of Anhui Province, China (Grant Nos. 1808085MF188 and 1808085QA21), and the Fundamental Research Funds for the Central Universities, China (Grant No. PA2019GDZC0098).

Abstract

Acoustic vortex (AV) beam is triggering the significant research interest in information and communication sciences due to its infinite and mutual orthogonal orbital angular momentums (OAMs). Therefore, measuring the topological charges of an AV beams become a task with great significance. In this work, we present a Fraunhofer diffraction (FD) pattern of an AV beam that can be used to quantitatively detect the OAMs of AV beams. We both theoretically and numerically investigate the FD patterns of AV beams passing through a multipoint interferometer (MPI). It is demonstrated that the topological charges of the AV beams can be determined from the interference intensity patterns. The proposed method may pave the way to the practical applications of AV beams.