Patent ID: 7321466

Claim:
A multi-element diffraction grating configured to diffract incident radiation with high dispersion using at least two holographic optical elements, said multi-element diffraction grating including: a Dickson grating having refractive index modulations of a first spatial frequency, wherein the Dickson grating is one of the holographic optical elements, and wherein the Dickson grating has a first polarization dependent loss, and wherein the incident radiation has both S-polarized components and P-polarized components having a range of wavelengths; and at least one additional volume phase grating, wherein each said additional volume phase grating is a non-Dickson grating, and wherein each said additional volume phase grating is another one of the holographic optical elements, the Dickson grating and each said additional volume phase grating are positioned relative to each other such that the radiation propagates through and is diffracted by said Dickson grating and each said additional volume phase grating, and each said additional volume phase grating has refractive index modulations of spatial frequency sufficiently lower than the first spatial frequency so that the multi-element diffraction grating has polarization dependent loss that does not differ significantly from the first polarization dependent loss and has at least substantially uniform diffraction efficiency across the range of wavelengths for the S-polarized components and the P-polarized components of the incident radiation.