An apparatus for processing electromagnetic radiation. The apparatus comprises a dielectric reflector, a plurality of ridges disposed on the dielectric reflector and a plurality of grooves disposed intermediate adjacent ridges to form a diffraction grating. Each of the ridges comprises a first dielectric material disposed on the dielectric reflector having a first index of refraction and a second dielectric material, having a second index of refraction different than the first index of refraction, disposed on the first dielectric material.