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Published on: July 18, 2015
Design, manufacturing, and performance analysis of mid-infrared achromatic half-wave plates with diamond
Christian Delacroix1, Pontus Forsberg, Mikael Karlsson
1Hololab, Université de Liège, Allée du 6 Août 17 B5a, B-4000 Liège, Belgium. delacroix@astro.ulg.ac.be
Abstract:
In this paper, we present a solution for creating robust monolithic achromatic half-wave plates (HWPs) for the infrared, based on the form birefringence of subwavelength gratings (SWGs) made out of diamond. We use the rigorous coupled wave analysis to design the gratings. Our analysis shows that diamond, besides its outstanding physical and mechanical properties, is a suitable substrate to manufacture mid-infrared HWPs, thanks to its high refractive index, which allows etching SWGs with lower aspect ratio. Based on our optimized design, we manufactured a diamond HWP for the 11-13.2 μm region, with an estimated mean retardance ~3.143±0.061 rad (180.08±3.51°). In addition, an antireflective grating was etched on the backside of the wave plate, allowing a total transmittance between 89% and 95% over the band.
