Interfaces with fractional optical constants and linear reflectance versus angle of incidence for incident unpolarized or circularly polarized light.

For unpolarized or circularly polarized light incident at a dielectric-conductor interface, the intensity reflectance R(ϕ) can be made an essentially linear function of the angle of incidence ϕ over a significant range of ϕ at specific values of the normal-incidence intensity reflectance R (≈1/3) and the associated normal-incidence reflection phase shift δ (≈40°). This places the complex refractive index n-jk of the interface in the domain of fractional optical constants. As demonstrated by specific examples, this is realizable in external reflection at vacuum-metal interfaces in the UV, and in internal reflection in the IR at interfaces between a transparent high-index substrate and an optically opaque thin film of the proper n and k. Fractional optical constants are also achievable for light reflection in air at planar surfaces of appropriately designed, nanostructured, metamaterial substrates.