Pushing the Limits of Broadband and High Frequency Metamaterial Silicon Antireflection Coatings

Abstract

Broadband refractive optics realized from high index materials provide compelling design solutions for the next generation of observatories for the Cosmic Microwave Background (CMB), and for sub-millimeter astronomy. In this paper, work is presented which extends the state of the art in silicon lenses with metamaterial antireflection (AR) coatings towards larger bandwidth and higher frequency operation. Examples presented include octave bandwidth coatings with less than $0.5\%$ reflection, a prototype 4:1 bandwidth coating, and a coating optimized for 1.4 THz. For these coatings the detailed design, fabrication and testing processes are described as well as the inherent performance trade offs.

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• SCUBA-2: The 10000 pixel bolometer camera on the James Clerk Maxwell Telescope
• Advanced ACTPol Cryogenic Detector Arrays and Readout
• SPT-3G: A Next-Generation Cosmic Microwave Background Polarization Experiment on the South Pole Telescope
• CLASS: The Cosmology Large Angular Scale Surveyor
• Large-aperture wide-bandwidth antireflection-coated silicon lenses for millimeter wavelengths
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• Full-sky beam convolution for cosmic microwave background applications
• QUBIC VI: cryogenic half wave plate rotator, design and performances
• Anti-reflection Coated Vacuum Window for the Primordial Inflation Polarization ExploreR (PIPER) balloon-borne instrument
• Cold optical design for the Large Aperture Simons Observatory telescope
• Simons Observatory: Broadband Metamaterial Anti-Reflection Cuttings for Large Aperture Alumina Optics