FINITE-WAVELENGTH EFFECT ON THE BALLISTIC PROPAGATION OF SURFACE ACOUSTIC-WAVES

We study the phonon-focusing effects of the Rayleigh and pseudosurface waves propagating ballistically on the (100) surface of cubic crystal s. Specifically, solving the wave equations for lattice displacements, we consider the finite-wavelength effect at the MHz-frequency range a nd for 1-cm propagation distance. The amplitude and polarization of la ttice displacements at the surface associated with surface waves are s ensitive to the propagation direction. Owing to this characteristic of surface waves, the focusing factor defined in the ray picture does no t necessarily describe correctly the intensity of surface waves excite d from a point source. The angular dependences of the calculated displ acement amplitudes explain an important feature of the recent focusing experiment of Rayleigh waves, which the simple theory based on the fo cusing factor fails to predict.