Taking magnetostatic surface wave diffraction as an example, this paper theoretically investigates the 2D diffraction pattern arising in the far-field region of a ferrite slab in the case of a plane wave with noncollinear group and phase velocities incident on a wide, arbitrarily oriented slit in an opaque screen. A universal analytical formula for the angular width of a diffracted beam is derived, which is valid for magnetostatic and other types of waves in anisotropic media and structures (including metamaterials) in 2D geometries. It is shown that the angular width of a diffracted beam in an anisotropic medium can not only take values greater or less than k 0 aD (where k 0 is the incident wavelength, and D is the slit width), but can also be zero under certain conditions.

In thispaper,some propertiesofasurfaceexciton in polyatomicpolarcrystalsare studied, Effective Hamiltonians in the ground state of the surface exciton for both strongcoupling and weak-couplingpolyatomic polar crystals are obtained by the method of alinear combination operator and simple unitary transformation. The effective mass of a strongcoupling surface exciton is derived using a Lagrange multiplier method. The self-trapping energy and effective potential of the surface exciton could be written as a series in ru;'. the lint term being proportional to rus, the coupling constant. The self-trapping energy and effective potential contain an extra contribution due to crossed t e r m between the different phonon branches. For a surface Wannier exciton the increasing part of the effective mass is proportional to a;

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