NIKA: A millimeter-wave kinetic inductance camera

¹ Institut Néel, CNRS & Université Joseph Fourier, BP 166, 38042 Grenoble, France e-mail: monfardini@grenoble.cnrs.fr
² Laboratoire d'Astrophysique, Observatoire de Grenoble, BP 53, 38041 Grenoble, France
³ SRON, Netherlands Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
⁴ SRON, Netherlands Institute for Space Research, Postbus 800, 9700 AV Groningen, The Netherlands
⁵ Cardiff School of Physics and Astronomy, Cardiff University, CF24 3AA, UK
⁶ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
⁷ Institut de RadioAstronomie Millimétrique, 300 rue de la Piscine, 38406 Saint-Martin d'Hères, France
⁸ Dipartimento di Fisica, Universitá di Roma La Sapienza, p.le A. Moro 2, 00185 Roma, Italy

Received: 2 April 2010
Accepted: 11 June 2010

Abstract

Context. Current generation millimeter wavelength detectors suffer from scaling limits imposed by complex cryogenic readout electronics. These instruments typically employ multiplexing ratios well below a hundred. To achieve multiplexing ratios greater than a thousand, it is imperative to investigate technologies that intrinsically incorporate strong multiplexing. One possible solution is the kinetic inductance detector (KID). To assess the potential of this nascent technology, a prototype instrument optimized for the 2 mm atmospheric window was constructed. Known as the Néel IRAM KID Array (NIKA), it has recently been tested at the Institute for Millimetric Radio Astronomy (IRAM) 30-m telescope at Pico Veleta, Spain.

Aims. There were four principle research objectives: to determine the practicality of developing a giant array instrument based on KIDs, to measure current in-situ pixel sensitivities, to identify limiting noise sources, and to image both calibration and scientifically-relevant astronomical sources.

Methods. The detectors consisted of arrays of high-quality superconducting resonators electromagnetically coupled to a transmission line and operated at ~100 mK. The impedance of the resonators was modulated by incident radiation; two separate arrays were tested to evaluate the efficiency of two unique optical-coupling strategies. The first array consisted of lumped element kinetic inductance detectors (LEKIDs), which have a fully planar design properly shaped to enable direct absorbtion. The second array consisted of antenna-coupled KIDs with individual sapphire microlenses aligned with planar slot antennas. Both detectors utilized a single transmission line along with suitable room-temperature digital electronics for continuous readout.

Results. NIKA was successfully tested in October 2009, performing in line with expectations. The measurement resulted in the imaging of a number of sources, including planets, quasars, and galaxies. The images for Mars, radio star MWC349, quasar 3C345, and galaxy M 87 are presented. From these results, the optical NEP was calculated to be around 1 × 10^-15 W/Hz^1/2. A factor of 10 improvement is expected to be readily feasible by improvements in the detector materials and reduction of performance-degrading spurious radiation.