Precise interferometric AO method for SAW velocity measurements in an anisotropic solid

We suggest an original method utilizing a two beam optical interferometer for the accurate SAW velocity measurements in an anisotropic solid. Namely, two parallel and spatially separated optical beams are diffracted from different points along the path of SAW propagation. Then at the output of the interferometer light beams of different orders (0, /spl plusmn/1) reflecting from the surface with SAW are combined in pairs to create the interference patterns. Measurement of the interference pattern's intensity oscillations versus the SAW frequency gives all needed information to determine the phase and the group SAW velocities and their dispersion. Experimental software includes: statistical data accumulation with auto correction of the interferometer phase change caused by a change of the external conditions, and Fourier analysis of interferometer signal spectrum with the use of generalized variables taking into account the SAW dispersion. The experimental error depends on the experimental peculiarities and is about 0.5 m/s for the phase velocity and 3 m/s for the group velocity. The method is tested by SAW velocity measurements on ST-quartz with a thin film of Al.