EFFECTIVE-MEDIUM THEORY OF ZEROTH-ORDER LAMELLAR GRATINGS IN CONICAL MOUNTINGS

A formalism is presented for calculating the ordinary and extraordinar y refractive indices for a uniaxial film with optical properties equiv alent to those of a conically mounted zeroth-order lamellar grating. I n the quasistatic limit (grating-period-to-wavelength ratio --> 0) thi s treatment is exact for both dielectric and metallic gratings. For pe riod-to-wavelength ratios approaching unity, the effective anisotropic refractive indices are dependent on the polar and azimuthal incidence angles. The validity of this method as the period-to-wavelength ratio increases is studied by comparison of the method with the predictions of rigorous grating theories. Comparisons are then made with the pred ictions of other effective-medium theories. Examples of the use of thi s theory for conically mounted zeroth-order gratings are presented.