Measurement and analysis of second-harmonic generation in focused vortex beams

Le résumé fourni par la source

Acoustic vortex beams have been a topic of interest since the late 1990s, with applications including acoustic tweezers, underwater communication, and biomedical procedures [Guo et al. J. Appl. Phys. 132, 210701 (2022)]. Understanding nonlinearity in acoustic vortex beams can be important in various contexts. Presented here are measurements of the amplitude and phase of beam profiles at the source frequency and second harmonic. The vortex beams were generated by a focused circular piston source of radius 1.9 cm and focal length 15.2 cm operating in water at 2.25 MHz in conjunction with additively manufactured phase plates corresponding to orbital numbers of 1 and 2. Measurements confirmed the predicted vortex ring radius in the focal plane at the source frequency [Gokani et al., JASA Express Lett. 4, 124001 (2024)]. To isolate the effects of acoustic nonlinearity from nonlinearity of the source transducer, hydrophone measurements were made over a range of distances from the source, and beam profiles were compared with numerical solutions of the Westervelt equation. Acoustic holography was used to characterize the source transducer with and without the phase plate in order to examine nonideal aspects of the source. [CAG was supported by the ARL:UT McKinney Fellowship in Acoustics.]

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