High-frequency monochromatic acoustic waves generated
by laser-induced thermomodulation
E. P. N. Damen, 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
Monochromatic acoustic waves are produced in a single crystal of
PbMoO4 by periodic heating of a deposited Au film over an area
about 40 µm in diameter by two interfering single-frequency dye
lasers. Detection of these waves at optical difference frequencies up to
4 GHz is accomplished by Brillouin scattering. The generated power
depends on the film thickness by acoustic interference within the film.
Besides weak phonon defocusing effects, the divergence of the generated
acoustic wave is limited by Fraunhofer diffraction.