23 July 2014 Fabrication of 721-pixel silicon lens array of an MKID camera
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Abstract
We have been developing a lens-integrated superconducting camera for millimeter and submillimeter astronomy. High-purity silicon (Si) is suitable for the lens array of the Microwave Kinetic Inductance Detector (MKID) camera due to the high refractive index and the low dielectric loss at low temperature. The camera is antenna-coupled Al coplanar waveguides on a Si substrate. Thus the lens and the device are made of the same material. We report a fabrication method of 721 pixel Si lens array with anti-reflection coating. The Si lens array was fabricated with an ultra-precision cutting machine. It uses TiAlN coated carbide end mills attached with a high-speed spindle. The shape accuracy was less than 50 μm peak-to-valley and the surface roughness was Ra 1.8 μm. The mixed epoxy was used as anti-reflection coating to adjust the refractive index. It was shaved to make the thickness of 185 μm for 220 GHz. Narrow grooves were made between the lenses to prevent cracking due to different thermal expansion coefficients of Si and the epoxy. The surface roughness of the anti-reflection coating was Ra 2.4 ~ 4.2 μm.
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Kenji Mitsui, Kenji Mitsui, Tom Nitta, Tom Nitta, Norio Okada, Norio Okada, Yutaro Sekímoto, Yutaro Sekímoto, Kenichi Karatsu, Kenichi Karatsu, Shigeyuki Sekiguchi, Shigeyuki Sekiguchi, Masakazu Sekine, Masakazu Sekine, Takashi Noguchi, Takashi Noguchi, } "Fabrication of 721-pixel silicon lens array of an MKID camera", Proc. SPIE 9153, Millimeter, Submillimeter, and Far-Infrared Detectors and Instrumentation for Astronomy VII, 91532T (23 July 2014); doi: 10.1117/12.2054846; https://doi.org/10.1117/12.2054846
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