Here we summarize the initial results from a complex field radiation pattern measurement of a kinetic inductance
detector instrument. These detectors are phase insensitive and have thus been limited to scalar, or amplitude-only, beam
measurements. Vector beam scans, of both amplitude and phase, double the information received in comparison to scalar
beam scans. Scalar beam measurements require multiple scans at varying distances along the optical path of the receiver
to fully constrain the divergence angle of the optical system and locate the primary focus. Vector scans provide this
information with a single scan, reducing the total measurement time required for new systems and also limiting the
influence of system instabilities. The vector scan can be taken at any point along the optical axis of the system including
the near-field, which makes beam measurements possible for large systems at high frequencies where these
measurements may be inconceivable to be tested in-situ. Therefore, the methodology presented here should enable
common heterodyne analysis for direct detector instruments. In principle, this coherent measurement strategy allows
phase dependent analysis to be performed on any direct-detect receiver instrument.
The main advantage of Microwave Kinetic Inductance Detector arrays (MKID) is their multiplexing capability, which allows for building cameras with a large number of pixels and good sensitivity, particularly suitable to perform large blank galaxy surveys. However, to have as many pixels as possible it is necessary to arrange detectors close in readout frequency. Consequently KIDs overlap in frequency and are coupled to each other producing crosstalk. Because crosstalk can be only minimised by improving the array design, in this work we aim to correct for this effect a posteriori. We analysed a MKID array consisting of 880 KIDs with readout frequencies at 4-8 GHz. We measured the beam patterns for every detector in the array and described the response of each detector by using a two-dimensional Gaussian fit. Then, we identified detectors affected by crosstalk above -30 dB level from the maximum and removed the signal of the crosstalking detectors. Moreover, we modelled the crosstalk level for each KID as a function of the readout frequency separation starting from the assumption that the transmission of a KID is a Lorenztian function in power. We were able to describe the general crosstalk level of the array and the crosstalk of each KID within 5 dB, so enabling the design of future arrays with the crosstalk as a design criterion. In this work, we demonstrate that it is possible to process MKID images a posteriori to decrease the crosstalk effect, subtracting the response of each coupled KID from the original map.
Microwave Kinetic Inductance Detectors (MKIDs) are becoming a very promising candidate for next generation imaging
instruments for the far infrared. A MKID consists of a superconducting resonator coupled to a feed-line used for the
readout. In the devices presented here radiation coupling is achieved by coupling the MKID directly to planar antenna.
The antenna is placed in the focus of an elliptical lens to increase the filling factor and to match efficiently to fore-optics.
In this paper we present the design and the optical performance of MKIDs optimized for operation at 350 GHz. We have
measured a device consisting of 14 pixels, characterized the coupling efficiency, antenna-lens frequency response and
beam pattern and compared these to theoretical simulations. The optical efficiency has been measured by means of a
black body radiator mounted in an ADR cryostat, through the variation of the black body temperature a variable
illumination of each pixel (from 0.1 fW to 2 pW) is achieved. The frequency response and beam pattern have been
directly measured in a He3 cryostat directly via the cryostat window and without the use of intermediate optics.
Kinetic Inductance Detectors (KID) are now routinely used in ground-based telescopes. Large arrays, deployed in
formats up to kilopixels, exhibit state-of-the-art performance at millimeter (e.g. 120-300 GHz, NIKA and NIKA2 on the
IRAM 30-meters) and sub-millimeter (e.g. 350-850 GHz AMKID on APEX) wavelengths. In view of future utilizations
above the atmosphere, we have studied in detail the interaction of ionizing particles with LEKID (Lumped Element KID)
arrays. We have constructed a dedicated cryogenic setup that allows to reproduce the typical observing conditions of a
space-borne observatory. We will report the details and conclusions from a number of measurements. We give a brief
description of our short term project, consisting in flying LEKID on a stratospheric balloon named B-SIDE.
Keywords: cryogenics detectors, millimeter-wave, superconducting resonators.
In the next decades millimeter and sub-mm astronomy requires large format imaging arrays and broad-band spectrometers to complement the high spatial and spectral resolution of the Atacama Large Millimeter/submillimeter Array. The desired sensors for these instruments should have a background limited sensitivity and a high optical efficiency and enable arrays thousands of pixels in size. Hybrid microwave kinetic inductance detectors consisting of NbTiN and Al have shown to satisfy these requirements. We present the second generation hybrid NbTiN-Al MKIDs, which are photon noise limited in both phase and amplitude readout for loading levels P850GHz < 10 fW. Thanks to the increased responsivity, the photon noise level achieved in phase allows us to simultaneously read out approximately 8000 pixels using state-of-the-art electronics. In addition, the choice of superconducting materials and the use of a Si lens in combination with a planar antenna gives these resonators the flexibility to operate within the frequency range 0:09 < v < 1:1 THz. Given these specifications, hybrid NbTiN-Al MKIDs will enable astronomically usable kilopixel arrays for sub-mm imaging and moderate resolution spectroscopy.
Distant, dusty and extremely luminous galaxies form a key component of the high redshift universe, tracing the period of intense cosmic activity that ultimately gave rise to the present-day universe. These highly luminous galaxies, first detected in the ground-based submillimeter region, are however optically very faint, which hampers identification of the optical counterpart and the measurement of a redshift. We are developing a new direct-detection submm spectrograph DESHIMA. By taking advantage of the rapidly advancing technology of superconducting microresonators, DESHIMA will revolutionize the appearance and capabilities of a submm spectrograph. There will no longer be large grating optics; instead DESHIMA will be equipped with a single chip, onto which the entire system of a dispersive filterbank and MKID sensor array is integrated. This chip will host 5000-10000 MKID sensors to instantaneously cover the entire submillimeter wave band (320-950 GHz) with a resolution of f/Δf = 1000, further multiplied by 6-9 spatial pixels. With the broader bandwidth and higher detector sensitivity, DESHIMA will be very efficient compared to ALMA in picking up THz lines from submm galaxies with unknown redshifts. The expected outcome of this project is; 1) a record of the properties and evolution of distant luminous galaxies, 2) a powerful and compact multi-purpose spectrometer suitable for future ground base telescopes as well as satellite missions, and 3) the emergence of a new branch of observational astronomy based on flexible on-chip submillimeter optics.
Kinetic Inductance Detectors (KIDs) with frequency domain read-out are intrinsically very suitable to use as
building blocks for very large arrays. KIDs therefore are an attractive detector option for the SAFARI instrument on
SPICA, Millimetron and also for large scale ground based imaging arrays. To study the properties of large KID
arrays we have fabricated 400 pixels array made from 40 nm thick Al films on high resistivity Si substrates. The
array is tested in a dry dilution refrigerator at 100 mK. We present the device design and experimental results. We
also present a new design of the array with lithographic air bridges over the coplanar waveguide feedline. The air
bridges are designed to suppress the slot line mode in the feedline and that will improve the pixel to pixel
reproducibility of large arrays.
The Lumped Element Kinetic Inductance Detector (LEKID) was first proposed in 2007 as a solution for using
kinetic inductance type detectors for sub-mm astronomy (450 - 200μm). Since then the LEKID has been
demonstrated to have applications over a much wider range of wavelength. Examples of this have been 200μm
detection of a cold blackbody and successful testing of a demonstration array operating at 2mm on the IRAM
telescope in October 2009. Due to the combination of absorber and detector in a single element, the LEKID is
an extremely simple detector to fabricate requiring only one deposition and etch step to produce an array of up
to 1000 pixels multiplexed onto a single feedline. The LEKID is also a very compact detector making it ideal
for producing arrays with high filling factors. The suitability of the LEKID for use in large arrays has prompted
a return visit to the IRAM telescope with a dual band instrument in 2010. This presentation will review the
progress to date of the LEKIDs development and outline design considerations for producing LEKIDs for future
FIR astronomical instruments such as SPICA. Also reviewed will be possible applications for the LEKID outside
sub-mm and mm astronomy.
We describe a new type of FIR detector based on lumped element superconducting resonators (LEKIDs). These
devices can act as distributed FIR radiation absorbers without the need for an additional coupling structure.
In addition, these devices can be integrated into a compact filled array geometry with high filling factor. We
describe the optimization of lumped element resonators for high coupling efficiency to incoming radiation in the
wavelength region from 200μm - 450μm, measurements of electrical and optical properties of these devices and
the design of a prototype array using these detectors.
The Japanese led Space Infrared telescope for Cosmology and Astrophysics (SPICA) will observe the universe over the
5 to 210 micron band with unprecedented sensitivity owing to its cold (~5 K) 3.5m telescope. The scientific case for a
European involvement in the SPICA mission has been accepted by the ESA advisory structure and a European
contribution to SPICA is undergoing an assessment study as a Mission of Opportunity within the ESA Cosmic Vision
1015-2015 science mission programme. In this paper we describe the elements that are being studied for provision by
Europe for the SPICA mission. These entail ESA directly providing the cryogenic telescope and ground segment
support and a consortium of European insitutes providing a Far Infrared focal plane instrument. In this paper we
describe the status of the ESA study and the design status of the FIR focal plane instrument.
Improved and reproducible heterodyne mixing (noise temperatures of 950 K at 2.5 THz) has been realized with NbN based hot-electron superconducting devices with low contact resistances. A distributed temperature numerical model of the NbN bridge, based on a local electron and a phonon temperature, has been used to understand the physical conditions during the mixing process. We find that the mixing is predominantly due to the exponential rise of the local resistivity as a function of electron temperature.
NbN hot electron bolometer (HEB) mixers are at this moment the best heterodyne detectors for frequencies above 1 THz. However, the fabrication procedure of these devices is such that the quality of the interface between the NbN superconducting film and the contact structure is not under good control. This results in a contact resistance between the NbN bolometer and the contact pad. We compare identical bolometers, with different NbN - contact pad interfaces, coupled with a spiral antenna. We find that cleaning the NbN interface and adding a thin additional superconductor prior to the gold contact deposition improves the noise temperature and the bandwidth of the HEB mixers with more than a factor of 2. We obtain a DSB noise temperature of 950 K at 2.5 THz and a Gain bandwidth of 5-6 GHz. For use in real receiver systems we design small volume (0.15x1 micron) HEB mixers with a twin slot antenna. We find that these mixers combine good sensitivity (900 K at 1.6 THz) with low LO power requirement, which is 160 - 240 nW at the Si lens of the mixer. This value is larger than expected from the isothermal technique and the known losses in the lens by a factor of 3-3.5.