High-Efficiency Multilayer Dielectric Diffraction Gratings
Diffraction gratings have been produced by mechanical ruling since 1883 and by interferometric or "holographic" techniques since the early 1970s. Whether produced by mechanical ruling or interferometric exposure, high diffraction efficiency is achieved in conventional reflection gratings by overcoating the grooves with a metal that exhibits high reflectance over the wavelength of interest. Most metallic gratings exhibit a diffraction efficiency determined by the shape and depth of the groove profile and the reflectivity of the metal. Due to the inherent broadband reflectivity of metals, frequency selectivity is accomplished only by dispersion. Finally, the low threshold for optical damage of metallic gratings limits their use with high power lasers.
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