| Chaotic optical microcavities attract a lot of interest for their photonic applications and usefulness in quantum chaos research. Although internal mode distributions of the deformed cavities reveal many interesting features, the mode characteristics are mainly studied in terms of far-field patterns and emission spectra. To supplement this limitation, we employ a water-filled ultrasonic cavity in which the pressure field satisfies the same Helmholtz equation as that of the optical electromagnetic wave in a microcavity. In this system, the spatial mode patterns can be easily obtained with the schlieren method. To study this system theoretically, we have performed simulations with boundary element method (BEM) and the results were in good agreements with the experiments. To confirm the accuracy of BEM calculation, the BEM results for a circular cavity were compared with the analytic solutions. Here we found that the imaginary part of the resonance frequency shows different aspects from that of a corresponding optical microcavity, exhibiting the effect of two critical angles of the liquid-solid interface. |
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