BIREFRINGENCE BY A SMOOTHLY INHOMOGENEOUS LOCALLY ISOTROPIC MEDIUM - 3-DIMENSIONAL CASE

The propagation problem for electromagnetic waves in a smoothly inhomo geneous locally isotropic medium, which was considered for a layered c ase in V. S. Liberman and B. Ya. Zel'dovich, Phys. Rev. E 49, 2389 (19 94) is generalized to a three-dimensional situation. Effective ''linea r'' birefringence, i.e., coherent transformation of a right circularly polarized wave into the left one with the amplitude similar to (lambd a/a) is predicted and calculated. It corresponds to the corrections de lta n similar to (lambda/a)(2) to the effective refractive index tense r, where a much greater than lambda is the size of smooth inhomogeneit y. An important feature is that linear birefringence appears only in t he presence of gradients of impedance rho(r) = root mu(r)/epsilon(r), whereas the gradients of refractive index n(r) = root epsilon(r)mu(r) are not necessary in a general three-dimensional case. This is in cont rast with a layered medium (one-dimensional case) where the net effect was proportional to the product (d ln rho/dz)(d ln n/dz).