Design and performance of dual-polarization lumped-element kinetic inductance detectors for millimeter-wave polarimetry

¹ Department of Physics, Columbia University, New York, NY 10027, USA
e-mail: hlm2124@columbia.edu
² School of Physics and Astronomy, Cardiff University, Cardiff, Wales CF24 3AA, UK
³ School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287, USA
⁴ Jet Propulsion Laboratory, Pasadena, CA 91109, USA
⁵ Code 665, Goddard Space Flight Center, Greenbelt, MD 20771, USA
⁶ Department of Physics and Astronomy, University of Southern California, Los Angeles, CA 90089, USA

Received: 4 October 2017
Accepted: 15 November 2017

Abstract

Aims. Lumped-element kinetic inductance detectors (LEKIDs) are an attractive technology for millimeter-wave observations that require large arrays of extremely low-noise detectors. We designed, fabricated and characterized 64-element (128 LEKID) arrays of horn-coupled, dual-polarization LEKIDs optimized for ground-based CMB polarimetry. Our devices are sensitive to two orthogonal polarizations in a single spectral band centered on 150 GHz with Δν∕ν = 0.2. The 65 × 65 mm square arrays are designed to be tiled into the focal plane of an optical system. We demonstrate the viability of these dual-polarization LEKIDs with laboratory measurements.

Methods. The LEKID modules are tested with an FPGA-based readout system in a sub-kelvin cryostat that uses a two-stage adiabatic demagnetization refrigerator. The devices are characterized using a blackbody and a millimeter-wave source. The polarization properties are measured with a cryogenic stepped half-wave plate. We measure the resonator parameters and the detector sensitivity, noise spectrum, dynamic range, and polarization response.

Results. The resonators have internal quality factors approaching 1 × 10⁶. The detectors have uniform response between orthogonal polarizations and a large dynamic range. The detectors are photon-noise limited above 1 pW of absorbed power. The noise-equivalent temperatures under a 3.4 K blackbody load are <100 μK √s. The polarization fractions of detectors sensitive to orthogonal polarizations are >80%. The entire array is multiplexed on a single readout line, demonstrating a multiplexing factor of 128. The array and readout meet the requirements for 4 arrays to be read out simultaneously for a multiplexing factor of 512.

Conclusions. This laboratory study demonstrates the first dual-polarization LEKID array optimized specifically for CMB polarimetry and shows the readiness of the detectors for on-sky observations.