Diffraction of coherent phonons emitted by a grating

Coherent acoustic phonons emitted by a grating are observed in the gigahert z range, and found to show well-resolved interference maxima on either side of the forward direction. The phonons are generated by laser-induced perio dic heating of a thin Au transducer, consisting of an array of narrow strip s deposited onto a (001) face of a single crystal of PbMoO4. The phase and group velocities, which are noncollinear due to the elastic anisotropy, are distinguished with reliance on Brillouin scattering. The results are in ac cord with optical diffraction theory in the Fraunhofer limit, provided phon on defocusing is taken into account. [S0163-1829(99)01541-6].