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18 February 2015 Fabrication of 721-pixel silicon lens array of a microwave kinetic inductance detector camera
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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.
© 2015 Society of Photo-Optical Instrumentation Engineers (SPIE) 2329-4124/2015/$25.00 © 2015 SPIE
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).
Published: 18 February 2015

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