Observation of scar modes in a deformed ultrasonic cavity

We employ an ultrasonic acoustic cavity in which the pressure field satisfies the same form of Helmholtz equation as the optical field in an optical microcavity of much interest, where many interesting features of mode distributions are expected but difficult to observe directly. Mode patterns in an acoustic cavity are measured with the Schlieren method, not perturbing the mode distributions at all. In addition, we have performed numerical simulations based on the boundary element method and compared the results with the experiment.