Loren J. Swenson

A Dual-band Millimeter-wave Kinetic Inductance Camera for the IRAM 30 m Telescope

The Neel IRAM KIDs Array (NIKA) is a fully integrated measurement system based on kinetic inductance detectors (KIDs) currently being developed for millimeter wave astronomy. The instrument includes dual-band optics allowing simultaneous imaging at 150 GHz and 220 GHz. The imaging sensors consist of two spatially separated arrays of KIDs. The first array, mounted on the 150 GHz branch, is composed of 144 lumped-element KIDs. The second array (220 GHz) consists of 256 antenna-coupled KIDs. Each of the arrays is sensitive to a single polarization; the band splitting is achieved by using a grid polarizer. The optics and sensors are mounted in a custom dilution cryostat, with an operating temperature of ~70 mK. Electronic readout is realized using frequency multiplexing and a transmission line geometry consisting of a coaxial cable connected in series with the sensor array and a low-noise 4 K amplifier. The dual-band NIKA was successfully tested in 2010 October at the Institute for Millimetric Radio Astronomy (IRAM) 30 m telescope at Pico Veleta, Spain, performing in-line with laboratory predictions. An optical NEP was then calculated to be around 2 × 10–16 W Hz–1/2 (at 1 Hz) while under a background loading of approximately 4 pW pixel–1. This improvement in comparison with a preliminary run (2009) verifies that NIKA is approaching the target sensitivity for photon-noise limited ground-based detectors. Taking advantage of the larger arrays and increased sensitivity, a number of scientifically relevant faint and extended objects were then imaged including the Galactic Center SgrB2 (FIR1), the radio galaxy Cygnus A, and the NGC1068 Seyfert galaxy. These targets were all observed simultaneously in the 150 GHz and 220 GHz atmospheric windows.

Design considerations for a background limited 350 micron pixel array using lumped element superconducting microresonators

Future submillimeter telescopes will demand arrays with 106 pixels to fill the focal plane. MAKO is a 350 μm camera being developed to demonstrate the use of superconducting microresonators to meet the high multiplexing factors required for scaling to large-format arrays while offering background-limited single-pixel sensitivity. Candidate pixel designs must simultaneously meet many requirements. To achieve the desired noise equivalent powers it must efficiently absorb radiation, feature a high responsivity, and exhibit low intrinsic device noise. Additionally, the use of high resonator quality factors of order ~ 105 and resonant frequencies of order fres ≈ 100 MHz are desirable in order to reduce the per-pixel bandwidth to a minimum set by telescope scan speeds. This allows a maximum number of pixels to be multiplexed in a fixed electronic bandwidth. Here we present measurement results of the first MAKO prototype array which meets these design requirements while demonstrating sufficient sensitivity for background-limited operation at ground-based, far-infrared telescopes.

MKID development for SuperSpec: an on-chip, mm-wave, filter-bank spectrometer

SuperSpec is an ultra-compact spectrometer-on-a-chip for millimeter and submillimeter wavelength astronomy. Its very small size, wide spectral bandwidth, and highly multiplexed readout will enable construction of powerful multibeam spectrometers for high-redshift observations. The spectrometer consists of a horn-coupled microstrip feedline, a bank of narrow-band superconducting resonator filters that provide spectral selectivity, and kinetic inductance detectors (KIDs) that detect the power admitted by each filter resonator. The design is realized using thin-film lithographic structures on a silicon wafer. The mm-wave microstrip feedline and spectral filters of the first prototype are designed to operate in the band from 195-310 GHz and are fabricated from niobium with at Tc of 9.2K. The KIDs are designed to operate at hundreds of MHz and are fabricated from titanium nitride with a Tc of ~ 2 K. Radiation incident on the horn travels along the mm-wave microstrip, passes through the frequency-selective filter, and is finally absorbed by the corresponding KID where it causes a measurable shift in the resonant frequency. In this proceedings, we present the design of the KIDs employed in SuperSpec and the results of initial laboratory testing of a prototype device. We will also brie describe the ongoing development of a demonstration instrument that will consist of two 500-channel, R=700 spectrometers, one operating in the 1-mm atmospheric window and the other covering the 650 and 850 micron bands.

MAKO: a pathfinder instrument for on-sky demonstration of low-cost 350 micron imaging arrays

Submillimeter cameras now have up to 104 pixels (SCUBA 2). The proposed CCAT 25-meter submillimeter telescope will feature a 1 degree field-of-view. Populating the focal plane at 350 microns would require more than 106 photon-noise limited pixels. To ultimately achieve this scaling, simple detectors and high-density multiplexing are essential. We are addressing this long-term challenge through the development of frequency-multiplexed superconducting microresonator detector arrays. These arrays use lumped-element, direct-absorption resonators patterned from titanium nitride films. We will discuss our progress toward constructing a scalable 350 micron pathfinder instrument focusing on fabrication simplicity, multiplexing density, and ultimately a low per-pixel cost.

A fast, ultra-sensitive and scalable detection platform based on superconducting resonators for fundamental condensed-matter and astronomical measurements

Low‐temperature physics and astronomy have traditionally focused on developing exquisitely sensitive single‐pixel detectors. While this has yielded considerable results, these technologies almost uniformly suffer from an inability to scale to large array sizes. In order to circumvent this barrier, frequency‐multiplexing techniques have recently emerged as a suitable solution. Here we present a detailed description of a measurement platform based on frequency‐multiplexed superconducting resonators along with the results from two distinct measurements that leverage this nascent technology to achieve multiple‐device readout. The first application discussed is a seven‐pixel array sensor of the permittivity of liquid helium suitable for quantum hydrodynamic experiments. The second implementation described is a prototype 16‐channel mm‐wavelength detector optimized for ground‐based astronomical detection at the 30 meter Institute for Millimeter‐Wave Radio Astronomy (IRAM) telescope in Pico Veleta, Spain.

SuperSpec: design concept and circuit simulations

SuperSpec is a pathfinder for future lithographic spectrometer cameras, which promise to energize extra-galactic astrophysics at (sub)millimeter wavelengths: delivering 200–500 kms-1 spectral velocity resolution over an octave bandwidth for every pixel in a telescope’s field of view. We present circuit simulations that prove the concept, which enables complete millimeter-band spectrometer devices in just a few square-millimeter footprint. We evaluate both single-stage and two-stage channelizing filter designs, which separate channels into an array of broad-band detectors, such as bolometers or kinetic inductance detector (KID) devices. We discuss to what degree losses (by radiation or by absorption in the dielectric) and fabrication tolerances affect the resolution or performance of such devices, and what steps we can take to mitigate the degradation. Such design studies help us formulate critical requirements on the materials and fabrication process, and help understand what practical limits currently exist to the capabilities these devices can deliver today or over the next few years.

Electromagnetic design for SuperSpec: a lithographically-patterned millimetre-wave spectrograph

SuperSpec is an innovative, fully planar, compact spectrograph for mm/sub-mm astronomy. SuperSpec is based on a superconducting filter-bank consisting of a series of planar half-wavelength filters to divide up the incoming, broadband radiation. The power in each filter is then coupled into titanium nitride lumped element kinetic inductance detectors, facilitating the read out of a large number of filter elements. We will present electromagnetic simulations of the different components that will make up an R = 700 prototype instrument. Based on these simulations, we discuss optimisation of the coupling between the antenna, transmission line, filters and detectors.

Status of SuperSpec: a broadband, on-chip millimeter-wave spectrometer

SuperSpec is a novel on-chip spectrometer we are developing for multi-object, moderate resolution (R = 100 − 500), large bandwidth (~1.65:1) submillimeter and millimeter survey spectroscopy of high-redshift galaxies. The spectrometer employs a filter bank architecture, and consists of a series of half-wave resonators formed by lithographically-patterned superconducting transmission lines. The signal power admitted by each resonator is detected by a lumped element titanium nitride (TiN) kinetic inductance detector (KID) operating at 100 – 200 MHz. We have tested a new prototype device that is more sensitive than previous devices, and easier to fabricate. We present a characterization of a representative R = 282 channel at f = 236 GHz, including measurements of the spectrometer detection efficiency, the detector responsivity over a large range of optical loading, and the full system optical efficiency. We outline future improvements to the current system that we expect will enable construction of a photon-noise-limited R = 100 filter bank, appropriate for a line intensity mapping experiment targeting the [CII] 158 μm transition during the Epoch of Reionization.

SWCam: the short wavelength camera for the CCAT Observatory

We describe the Short Wavelength Camera (SWCam) for the CCAT observatory including the primary science drivers, the coupling of the science drivers to the instrument requirements, the resulting implementation of the design, and its performance expectations at first light. CCAT is a 25 m submillimeter telescope planned to operate at 5600 meters, near the summit of Cerro Chajnantor in the Atacama Desert in northern Chile. CCAT is designed to give a total wave front error of 12.5 μm rms, so that combined with its high and exceptionally dry site, the facility will provide unsurpassed point source sensitivity deep into the short submillimeter bands to wavelengths as short as the 200 μm telluric window. The SWCam system consists of 7 sub-cameras that address 4 different telluric windows: 4 subcameras at 350 μm, 1 at 450 μm, 1 at 850 μm, and 1 at 2 mm wavelength. Each sub-camera has a 6’ diameter field of view, so that the total instantaneous field of view for SWCam is equivalent to a 16’ diameter circle. Each focal plane is populated with near unit filling factor arrays of Lumped Element Kinetic Inductance Detectors (LEKIDs) with pixels scaled to subtend an solid angle of (λ/D)2 on the sky. The total pixel count is 57,160. We expect background limited performance at each wavelength, and to be able to map < 35(°)2 of sky to 5 σ on the confusion noise at each wavelength per year with this first light instrument. Our primary science goal is to resolve the Cosmic Far-IR Background (CIRB) in our four colors so that we may explore the star and galaxy formation history of the Universe extending to within 500 million years of the Big Bang. CCATs large and high-accuracy aperture, its fast slewing speed, use of instruments with large format arrays, and being located at a superb site enables mapping speeds of up to three orders of magnitude larger than contemporary or near future facilities and makes it uniquely sensitive, especially in the short submm bands.