Structured metal double-blazed dispersion grating for broadband spectral efficiency achromatization.

The majority of spectrometers use reflective dispersion gratings with a metal-coated blazed grating profile for spectral decomposition. They achieve high diffraction efficiency at the design wavelength, which decays considerably in the adjacent longer and shorter wavelength ranges. We introduce a structured metal double-blazed grating with a high diffraction efficiency for a broadband spectral range, consisting of a sawtooth-like structured metal surface filled with a first dielectric transparent material. The planarized upper surface is covered with a second blazed profile of a different transparent material. We present a systematical theoretical analysis of the diffraction efficiency in reflection geometry, based on a scalar approach involving fundamental dispersion parameters such as Abbe numbers and relative partial dispersions of the materials. We find material combinations reducing the profile heights down to 1-2 µm.