Abstract: The diffraction phenomena of the normally incident SAW on acoustic gratings are investigated. The acoustic grating which is comprised of an array of aluminium film stripes was fabricated on the surface of Y-cut LiNbO₃ on which the SAW propagates.
The phenomenologicall method is used to analyze the diffraction characteristics of the grating upon which the SAW beam normally impinges. The emphasis is laid on two special cases, i.e., "thin grating" and "thick grating". For the former, the Raman-Nath approximation are quoted from the theory of the acousto-optical diffraction. For the latter, the analytical expressions of the diffracted acoustic intensities are derived by means of the normal modes theory
Experimentally, some interesting results are obtained by using optical methods. The images of the intensity distribution of the diffracted acoustic fields for some cases as well as the SAW wavefronts within acoustic grating and at near field are visualized; the angles of diffraction and intensities of the diffracted waves of different orders at different frequencies are measured. Fi-nally, the comparison between experimental and theoretical results are given.