Schlieren-Style Stroboscopic Nonscan Imaging Of The Field-Amplitudes Of Acoustic Whispering Gallery Modes

We report a schlieren-style stroboscopic phase-contrast field-amplitude imaging of two-dimensional acoustic whispering gallery modes in a circular shell cavity immersed in liquid. A schlieren signal is combined with a presplit reference beam to enable nonscan field-amplitude imaging. Excitation mechanisms of standing and traveling eigenmodes, respectively, are analyzed with acoustic ray simulations presented in a Poincare surface of sections. The time evolutions for both standing and traveling eigenmodes are reconstructed using the stroboscopic capability. (C) 2020 Optical Society of America