High efficiency phase grating having a planar reflector

1. An apparatus for processing electromagnetic radiation, comprising:

a substrate;

a plurality of ridges each having a top surface, said ridges being disposed on the substrate and a plurality of grooves disposed intermediate adjacent ridges to form a diffraction grating, each of said ridges comprising a first dielectric material disposed on the substrate 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; and

an overcoat layer having a planar surface that is coplanar with the top surfaces of said ridges;

wherein the diffraction grating is constructed and ananged such that the zeroth diffraction orders of a TM-polarized portion and a TE-polarized portion of the electromagnetic radiation are substantially canceled by destructive interference for an angle of incidence of the radiation on the diffraction grating.

2. The apparatus as claimed in claim 1 , wherein the first dielectric material and the second dielectric material are absent from the grooves.

3. The apparatus as claimed in claim 1 , wherein the substrate is a transparent substrate.

4. The apparatus as claimed in claim 1 , wherein the substrate comprises a dielectric reflector.

5. The apparatus as claimed in claim 4 , wherein the dielectric reflector comprises a dielectric stack mirror.

6. The apparatus as claimed in claim 5 , wherein the dielectric stack mirror comprises alternating layers of TiO 2 and SiO 2 .