Diffraction of coherent phonons emitted by a grating
D. J. Dieleman, A. F. Koenderink, A. F. M. Arts, and H. W. de Wijn
Faculty of Physics and Astronomy, and Debye Research Institute, Utrecht
University, P.O. Box 80.000, 3508 TA Utrecht, The Netherlands
Coherent acoustic phonons emitted by a grating are observed in the
gigahertz range, and found to show well-resolved interference maxima on
either side of the forward direction. The phonons are generated by
laser-induced periodic heating of a thin Au transducer, consisting of an
array of narrow strips 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 accord with optical diffraction
theory in the Fraunhofer limit, provided phonon defocusing is taken into
account.