Observation of waves propagating within a substrate

We developed a technique for observing the distribution of acoustic waves based on polarization detection. This technique enabled visualization of wave distributions in an LiTaO₃ substrate at various depths. Significant differences of the distribution in the substrate were observed at different frequencies. At the resonant frequency, the waves were distributed near the surface of the resonator. In contrast, a non-negligible amount of the acoustic wave was detected in a deeper area (4λ) above the anti-resonant frequency. This improved technique enables us to observe the behavior of acoustic waves both on the surface and in the substrate.