Development of high-throughput silicon lens and grism with moth-eye antireflection structure for mid-infrared astronomy

摘要

We have been developing high-throughput optical elements with the moth-eye structures for mid-infrared opticalsystems. The moth-eye structures are optimized for the wavelength of 25-45μm. It consists of cones with aheight of 15-20μm arranged at an interval of 5μm. They are formed on silicon substrate by electron-beamlithography and reactive ion etching. As a verification of the usefulness of moth-eye, a double-sided moth-eyesilicon plane was fabricated. It shows a transmittance increase of 60% compared with the unprocessed siliconplane. As the first trial of the moth-eye optical element, two silicon lenses with single-sided moth-eye werefabricated. One is a plane-convex lens with the moth-eye on the convex surface. The size of the moth-eyeformed region is 30 mm x 30 mm. Its focal length is 186 mm. The other one is a biconvex lens with moth-eyeformed region of Φ 33 mm and a focal length of 94 mm. Uniform moth-eye pattern was fabricated especiallyfor the second lens sample. Imaging test with the first sample showed that neither image degradation nor focallength variation was induced by the moth-eye fabrication. As a step to grism with moth-eye, a moth-eye gratingsample was fabricated. The grating pattern (Grating constant: 124.9μm, Blaze angle: 4 deg) was successfullyfabricated with anisotropic etching. Moth-eye patterns were fabricated on the grating surface. Although theresulted moth-eye was successfully fabricated in the most regions, some non-uniformity was found. It can beattributed 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.