Optical Probing of Acoustic Surface Waves

Light diffraction by acoustic surface waves is used as a probe to study the propagation characteristics of Rayleigh waves on y-cut z-oriented LiNbO3. Both the surface deformation and the periodic variation of the index of refraction in the medium, which diffracts the transmitted light beam, are related to the particle displacements of the propagating Rayleigh waves. For the reflected beam, only the surface deformation contributes to the diffracted light. Experimental demonstrations of using the optical probe to observe the Fresnel diffraction of a rectangular interdigital transducer to measure the transmission and reflection coefficients of a transducer and to determine the propagation characteristics, such as velocity, attenuation of Rayleigh waves on a LiNbO3 substrate and on a metalized LiNbO3 substrate, will be discussed.