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13 September 2012 Development of high-throughput silicon lens and grism with moth-eye antireflection structure for mid-infrared astronomy
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We have been developing high-throughput optical elements with the moth-eye structures for mid-infrared optical systems. The moth-eye structures are optimized for the wavelength of 25-45μm. It consists of cones with a height of 15-20μm arranged at an interval of 5μm. They are formed on silicon substrate by electron-beam lithography and reactive ion etching. As a verification of the usefulness of moth-eye, a double-sided moth-eye silicon plane was fabricated. It shows a transmittance increase of 60% compared with the unprocessed silicon plane. As the first trial of the moth-eye optical element, two silicon lenses with single-sided moth-eye were fabricated. One is a plane-convex lens with the moth-eye on the convex surface. The size of the moth-eye formed region is 30 mm x 30 mm. Its focal length is 186 mm. The other one is a biconvex lens with moth-eye formed region of Φ 33 mm and a focal length of 94 mm. Uniform moth-eye pattern was fabricated especially for the second lens sample. Imaging test with the first sample showed that neither image degradation nor focal length variation was induced by the moth-eye fabrication. As a step to grism with moth-eye, a moth-eye grating sample was fabricated. The grating pattern (Grating constant: 124.9μm, Blaze angle: 4 deg) was successfully fabricated with anisotropic etching. Moth-eye patterns were fabricated on the grating surface. Although the resulted moth-eye was successfully fabricated in the most regions, some non-uniformity was found. It can be attributed to unevenness of resist coating, and improvement of coating method is needed.
© (2012) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Takafumi Kamizuka, Takashi Miyata, Shigeyuki Sako, Hiroaki Imada, Tomohiko Nakamura, Kentaro Asano, Mizuho Uchiyama, Kazushi Okada, Takehiko Wada, Takao Nakagawa, Takashi Onaka, and Itsuki Sakon "Development of high-throughput silicon lens and grism with moth-eye antireflection structure for mid-infrared astronomy", Proc. SPIE 8450, Modern Technologies in Space- and Ground-based Telescopes and Instrumentation II, 845051 (13 September 2012);

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