Anisotropic diffraction of bulk acoustic wave beams in lithium niobate

• Diffraction of BAW in lithium niobate single crystals was studied theoretically.
• Diffractional coefficients were derived as the estimates for curvature of the slowness surface.
• The diffractional coefficients were calculated for arbitrary wave vector directions.

The formalism of planar diffraction tensor was applied to the analysis of anisotropy of bulk acoustic wave diffraction and to build a full map of anisotropic diffractional coefficients for three bulk acoustic wave modes propagating in lithium niobate. For arbitrary propagation direction the diffractional coefficients derived allow estimation of ultrasonic beam divergence in far-field. Analysis of obtained data revealed that the maxima of acousto-optic figure of merit for anisotropic diffraction in the YZ plane correspond to moderate diffractional spreading of the beams exceeding isotropic diffraction 2–3 times.