Coupling of Electromagnetic Waves in CdS

A theoretical and experimental study is made of the coupling of the ordinary and extraordinary electro-magnetic waves in CdS. The coupling, which may be induced by an external magnetic field or stress, occurs only at energies near the accidental crossing of the index-of-refraction curves $n_0\mathrm{}\left(E\right)\mathrm{}$ and $n_e\mathrm{}\left(E\right)\mathrm{}$. This effect was pointed out by J. J. Hopfield and D. G. Thomas, who showed that this condition, when combined with the anisotropic optical absorption present in the crystal, leads to a discrete absorption line. The oscillatory behavior of the coupled energy and the magnitude of these absorption effects are quantitatively explained. These effects can be used to produce a unique type of optical filter which may be either band-pass or band-reject. Finally, the Faraday rotation in CdS normal to the optic axis is measured at the isotropic point.