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Development of confocal picosecond ultrasonics for visualizing propagation of an acoustic wave

For visualizing propagation of an acoustic wave and evaluating the local sound velocity in micro/nano-meter structures, confocal picosecond ultrasonics is developed. In conventional picosecond ultrasonics, the measurement of local sound velocity was difficult, and macroscopic sound velocity and elastic properties were measured. However, in confocal picosecond ultrasonics, a confocal laser-scanning microscope is embedded in the optics of the picosecond ultrasonics, and the depth resolution is improved. Using the developed optics, we successfully observed propagation of an acoustic wave in thin film. In this paper, the optics we developed and the experimental results on silica film are reported.