Unidirectional bulk acoustic wave excitation by scanning interference fringes and its application to acoustical imagings

Excitation of high-frequency bulk acoustic waves (BAW) using scanning interference fringes (SIF) is presented. The SIF are produced by intersecting two coherent laser beams with different frequencies on an opaque specimen. It is possible to generate unidirectional BAW which propagate into the specimen by this method. Propagation direction of the BAW is determined by the phase-matching condition between the SIF and the wave front of the BAW at the surface, which could be controlled by incident angles of laser beams. The principle and verification of this method are briefly described in the first part. Application to the BAW velocity measurement was introduced and was experimentally verified using Si₃N₄ specimen. Acoustical imagings taken by the BAW generation method were also shown in the last part