GREEN-FUNCTION OF THE ELECTROMAGNETIC-FIELD IN BIAXIAL MEDIA

Asymptotic properties of the Green's function of an electromagnetic field in the far zone of biaxial anisotropic media are examined, based on ideas proposed by Lax and Nelson [Phys. Rev. B 4, 3694 (1971)]. The rather complicated structure of the wave surface and the ray surface, in particular the existence of their singular points, is taken into account. Starting from a detailed analysis of the wave-surface Gaussian curvature, we find the directions of Green's-function asymptotic behavior differing from the usual R-1 relationship. These directions are the directions along the biradials of a biaxial medium, and the infinite sets of directions defined by a wave vector directed along every one of the binormals. In the first case, the asymptotical form of the Green's function is proportional to R-1/2; in the second case, this asymptotical form is proportional to R-5/4. A smooth transition from the asymptotic form proportional to R-1/2 to the usual asymptotic form is analyzed. The possibility of an experimental observation of this unusual asymptotic behavior is discussed.