GREEN-FUNCTION OF THE ELECTROMAGNETIC-FIELD IN BIAXIAL MEDIA

Asymptotic properties of the Green's function of an electromagnetic fi eld in the far zone of biaxial anisotropic media are examined, based o n 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 ac count. Starting from a detailed analysis of the wave-surface Gaussian curvature, we find the directions of Green's-function asymptotic behav ior differing from the usual R-1 relationship. These directions are th e 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 Gree n's function is proportional to R-1/2; in the second case, this asympt otical form is proportional to R-5/4. A smooth transition from the asy mptotic form proportional to R-1/2 to the usual asymptotic form is ana lyzed. The possibility of an experimental observation of this unusual asymptotic behavior is discussed.