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29 December 2003 Blazed-binary diffractive gratings with antireflection coating for improved operation at 10.6 μm
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Blazed-binary optical elements are diffractive components, composed of subwavelength ridges, pillars or other simple geometries carefully etched in a dielectric film, that mimic standard blazed-echelette diffractive elements. Recent experimental results in the visible showed that, blazed-binary optical elements offer high diffraction efficiencies and unique properties that cannot be achieved by standard echelette diffractive elements. Meanwhile, the manufacture of these optical elements for operation in the visible represents a challenge for today’s technologies since they involve both sub-micron sizes and high aspect ratios. In this paper, we extend the study to the thermal infrared, where the fabrication constraints are compatible with simple manufacture process such as photolithography. A 3λ-period blazed-binary grating etched into a silicon substrate, implementing an antireflection function (zinc sulphide deposition over the etched structure), was designed for operation under TM polarization at 10.6 μm. Its fabrication involved contact photolithography, reactive ion etching and an evaporation deposition over the etched structure. A first-order transmitted diffraction efficiency of 80 % was measured under TM polarization at 10.6 μm. This result validates the use photolithography, a low-cost technology, and an antireflection deposition, for the manufacture of efficient blazed-binary diffractive elements operating for thermal imaging (8-12μm infrared band).
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Mane-Si Laure Lee, Jean-Claude Rodier, Philippe Lalanne, Pierre Legagneux, Patrick Gallais, Chantal Germain, and Joel Rollin "Blazed-binary diffractive gratings with antireflection coating for improved operation at 10.6 μm", Proc. SPIE 5184, Physics, Theory, and Applications of Periodic Structures in Optics II, (29 December 2003);


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