Fabrication of 721-pixel silicon lens array of a microwave kinetic inductance detector camera

Kenji Mitsui; Tom Nitta; Norio Okada; Yutaro Sekimoto; Kenichi Karatsu; Shigeyuki Sekiguchi; Masakazu Sekine; Takashi Noguchi

doi:10.1117/1.JATIS.1.2.025001

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18 February 2015 Fabrication of 721-pixel silicon lens array of a microwave kinetic inductance detector camera

Kenji Mitsui, Tom Nitta, Norio Okada, Yutaro Sekimoto, Kenichi Karatsu, Shigeyuki Sekiguchi, Masakazu Sekine, Takashi Noguchi

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J. of Astronomical Telescopes, Instruments, and Systems, 1(2), 025001 (2015). https://doi.org/10.1117/1.JATIS.1.2.025001

Abstract

We have been developed 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 camera due to its high refractive index and low dielectric loss at low temperatures. The camera is an antenna-coupled Al coplanar waveguide on a Si substrate. Thus the lens and the device are made of the same material. We report a fabrication method of a 721-pixel Si lens array with an antireflection (AR) coating. The Si lens array was fabricated with an ultraprecision 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 arithmetic average roughness (Ra) of 1.8 μm. The mixed epoxy was used as an AR coating to adjust the refractive index. It was shaved to yield a thickness of 185 μm for 220 GHz. Narrow grooves were made between the lenses to prevent cracking due to the different thermal expansion coefficients of Si and the epoxy. The surface roughness of the AR coating was Ra of 2.4 to 4.2 μm.

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Kenji Mitsui, Tom Nitta, Norio Okada, Yutaro Sekimoto, Kenichi Karatsu, Shigeyuki Sekiguchi, Masakazu Sekine, and Takashi Noguchi "Fabrication of 721-pixel silicon lens array of a microwave kinetic inductance detector camera," Journal of Astronomical Telescopes, Instruments, and Systems 1(2), 025001 (18 February 2015). https://doi.org/10.1117/1.JATIS.1.2.025001

Published: 18 February 2015

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