Acousto-optic imaging of focused ultrasound pressure fields

Focused sound field measurements typically involve needle- or membrane-type transducers stepped across the sound field. This process produces an apparent image of the sound field limited by probe linearity, effective aperture size, and experimental alignment. Historically, acousto-optic schlieren imaging has provided an effective, qualitative technique for examining a sound-pressure field. In this paper the schlieren technique is extended to provide quantitative measurements of the peak focused sound-pressure field without in situ disruptions. A numerical solution of the Khokhlov–Zabolotskaya–Kuznetsov parabolic equation is used to predict the sound-pressure field for a line focused transducer. Enhancements in the standard numerical solution include a floating boundary condition and an adaptive technique for adjusting the computation effectiveness consistent with nonlinearity induced harmonic growth. Key features of the experimental setup are outlined and theoretical predictions compared with experimental measurements made with the extended schlieren technique.