Two-dimensional diffraction catastrophe on an anisotropic substrate

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Abstract
The two-dimensional diffraction catastrophe forms on an anisotropic substrate are studied. According to the catastrophe theory, they separately belong to fold caustics and cusp ones. The acoustic fields associated with these caustics are also classified into two categories, and can be expressed by the Airy function and the Pearcy function, respectively. The forms of these two kinds of caustics have been determined by these expressions of the acoustic fields. The experimental verifications have been provided by the surface acoustic wave (SAW) field excited by a circular arc interdigital transducer on YZ-LiNbO3. By means of the dark-field method, we have obtained photographs of SAW caustics. The experimental results agree with our theoretical calculations. We have concluded that it is the velocity anisotropy of the substrate that causes these two kinds of caustics.

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