The Origins Space Telescope (OST) is a NASA study for a large satellite mission to be submitted to the 2020 Decadal Review. The proposed satellite has a fleet of instruments including the HEterodyne Receivers for OST (HERO). HERO is designed around the quest to follow the trail of water from the ISM to disks around protostars and planets. HERO will perform high-spectral resolution measurements with 2x9 pixel focal plane arrays at any frequency between 468GHz to 2,700GHz (617 to 111 μm). HERO builds on the successful Herschel/HIFI heritage, as well as recent technological innovations, allowing it to surpass any prior heterodyne instrument in terms of sensitivity and spectral coverage.
With increasing array size, it is increasingly important to control stray radiation inside the detector chips themselves. We demonstrate this effect with focal plane arrays of absorber coupled Lumped Element microwave Kinetic Inductance Detectors (LEKIDs) and lens-antenna coupled distributed quarter wavelength Microwave Kinetic Inductance Detectors (MKIDs). In these arrays the response from a point source at the pixel position is at a similar level to the stray response integrated over the entire chip area. For the antenna coupled arrays, we show that this effect can be suppressed by incorporating an on-chip stray light absorber. A similar method should be possible with the LEKID array, especially when they are lens coupled.
Complex field measurements are increasingly becoming the standard for state-of-the-art astronomical instrumentation. Complex field measurements have been used to characterize a suite of ground, airborne, and space-based heterodyne receiver missions,1-6 and a description of how to acquire coherent field maps for direct detector arrays was demonstrated in Davis et. al. 20177. This technique has the ability to determine both amplitude and phase radiation patterns from individual pixels on an array for direct comparison to optical simulations. Phase information helps to better characterize the optical performance of the array (as compared to total power radiation patterns) by constraining the fit in an additional plane.4 This is a powerful technique to diagnose optical alignment errors through the optical system, as a complex field scan in an arbitrary plane can be propagated either forwards or backwards through optical elements to arbitrary planes along the principal axis. Complex radiation patterns have the advantage that the effects of optical standing waves and alignment errors between the scan system and the instrument can be corrected and removed during post processing.
Here we discuss the mathematical framework used in an analysis pipeline developed to process complex field radiation pattern measurements. This routine determines and compensates misalignments of the instrument and scanning system. We begin with an overview of Gaussian beam formalism and how it relates to complex field pattern measurements. Next we discuss a scan strategy using an offset in z along the optical axis that allows first-order optical standing waves between the scanned source and optical system to be removed in post-processing. Also discussed is a method by which the co- and cross-polarization fields can be extracted individually for each pixel by rotating the two orthogonal measurement planes until the signal is the co-polarization map is maximized (and the signal in the cross-polarization field is minimized). We detail a minimization function that can fit measurement data to an arbitrary beam shape model. We conclude by discussing the angular plane wave spectral (APWS) method for beam propagation, including the near-field to far-field transformation.
The Atacama Large Millimeter Array (ALMA) project requires the development of reliable quasi-optical systems with requirements similar to the ones in space. The operating condition for optical elements of higher frequency channels are similar to the conditions in spacecraft, since these elements are contained within the ALMA cryostat in high vacuum and at cryogenic temperatures. The remote terrain of the Atacama Desert and the scale of project suggest that a significant effort should be made to ensure high reliability of the system. Therefore the techniques, common to a space mission are applied with this development.
In this report we would like to present the design of the quasi-optical system for ALMA band 9 (600-702 GHz) containing elements typical to a space system. A design assumptions and details will be presented for a frequency independent system. A measurement of near field antenna beam pattern (phase and amplitude) will be presented and comparison with theoretical predictions will be made.
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.
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.
SPACEKIDS, a European Union FP-7 project, has recently been completed. It has focused on developing kinetic
inductance detector (KID) arrays and demonstrating their suitability for space applications at far infrared and
submillimetre wavelengths. KID arrays have been developed for both low-background (typical of astrophysical
applications) and high-background (typical of Earth-observation applications), based on performance specifications
derived from the science requirements of representative potential future missions. KID pixel and array designs have
been developed, together with readout electronics necessary to read out large numbers of pixels. Two laboratory
demonstrator systems have been built and used for comprehensive evaluation of large-format array characteristics and
performance in environments representative of both astronomy and Earth observing applications. We present an
overview of the SPACEKIDS project and a summary of its main results and conclusions.
In the modular sideband-separating mixers that we built over the last years, we observe a clear anti-correlation
between the image rejection ratio obtained with a certain block and its noise performance, as well as strong
correlations between the image rejection and imbalances in the pumping of the mixer devices.
We report on the mechanisms responsible for these effects, and conclude that the reduction of the image
rejection is largely explained by the presence of standing waves. We demonstrate the rejection ratio to be
very sensitive to those. In principle, all potential round-trip paths should be terminated in matched loads, so no
standing waves can develop. In practice, the typical high reflections from the SIS mixers combined with imperfect
loads and non-negligible input/output reflections of the other components give many opportunities for standing
waves. Since most of the loss of image rejection can be attributed to standing waves, the anti-correlation with
the noise temperature can be understood by considering any excess loss in the structure, as the waveguides start
acting as distribured loads. This reduces the standing waves, and thereby improves the rejection ratio, at the
expense of noise temperature.
Based on these experiences, we designed a new waveguide structure, with a basic waveguide size of 400×200 μm
and improved loads. Strong emphasis was placed on low input and output reflections of the waveguide components,
in some places at the cost of phase or amplitude imbalance. For the latter there is ample margin not to
impair the performance, however. Apart from further details of the design, we present the first results of the
new mixers, tested in a modified production-level ALMA Band 9 receiver, and show that even in an unfinished
state, it simultaneously meets requirements for image rejection and noise temperature.
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.
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.
The international far-infrared astrophysics community is eager to follow up Spitzer and Herschel observations with
sensitive, high-resolution imaging and spectroscopy, for such measurements are needed to understand merger-driven star
formation, Active Galactic Nuclei, chemical enrichment in galaxies, star and planetary system formation, and the
development and prevalence of water-bearing planets. Through concerted efforts worldwide, the key enabling
technologies are maturing. NASA sponsored the SPIRIT Probe and SPECS flagship-class mission concept studies during
the past decade. Experiments involving interferometry testbeds are underway in the UK and the US. With new EU
Seventh Framework Programme support, the European community is undertaking science definition studies and
investing in enabling technology for a future space far-IR interferometry mission. The Japanese balloon-borne far-IR
interferometer FITE is being prepared for its maiden flight, and NASA’s BETTII balloon interferometer is under
development, with contributions from the UK. This paper reviews recent technical progress, summarizes mission design
tradeoffs, and offers a vision for space-based far-IR interferometry involving international collaboration.
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.
For high-frequency observational bands like ALMA (Atacama Large Millimeter Array) Band 9 (600—720 GHz), which
tend to be dominated by atmospheric noise, implementation of sideband-separating mixers can reduce, up to a factor of
two, the integration time needed to reach a certain signal-to-noise ratio for spectral line observations. Because of very
high oversubscription factor for observation in ALMA Band 9, an upgrade of the current Double Sideband (DSB) mixer
to a Two Sideband (2SB) configuration is a promising option for future ALMA development.
Here we present a developed 2SB mixer and a modified cartridge design. The 2SB mixer includes a waveguide RF
hybrid block, which have been produced on a micro-milling machine and equipped with standard Band 9 SIS mixer
devices. These two SIS mixers have been separately tested in DSB mode. The SSB noise temperature is within the
ALMA requirements of 336 K over 80% of the band, and 500 K over the entire band. The 2SB mixer has the sideband
rejection ratio better than 12 dB over the full RF band, which is also well within the ALMA specifications of 10 dB.
We present an overview of the current status of the space mission Millimetron. Millimetron is a large 10-m
cooled space telescope optimized for operation in the submillimeter and far infrared wavelengths. This mission
will be able to contribute to the solution of several key problems in astrophysics, such as study of the formation
and evolution of stars and planets, galaxies, quasars and many others. The telescope will have an unprecedented
sensitivity in the single-dish observation mode and an extremely high spatial resolution as an element of a
ground-space very long baseline interferometry (VLBI) system. The mission will have a cryogenic instruments
and antenna, which will be cooled passively with radiation shields and actively with mechanical coolers. With
this cooling combination the 10-m space telescope may reach a temperature of about 4.5 K. The Millimetron is
proposed as a Russian-led mission with an extensive international consortium in various countries. The mission
launch is planned for 2017.
The ALMA Band 9 receiver cartridge (600-720 GHz) based on Dual Sideband (DSB) superconductor-insulatorsuperconductor
(SIS) mixer is currently in full production. In the case of spectral line observations, the integration time
to reach a certain signal-to-noise level can be reduced by about a factor of two by rejecting an unused sideband. The goal
is to upgrade the current ALMA band 9 cartridge to a full dual-polarization sideband separating (2SB) capability, with
minimal-cost upgrade path. A new compact and modular sideband separating mixer was designed, and a prototype
manufactured. The individual SIS mixer devices in the 2SB block are implemented as conventional Band 9 DSB mixers,
so that existing devices can be reused and tested individually. Any ALMA DSB developments contribute to the 2SB
upgrade. The first experimental results demonstrate noise temperature from 300K to 500K over 80% of the band, which
will be improved to fit the ALMA requirements. Nevertheless, the frequency response for 2SB is the same as for DSB,
showing that the RF design is still valid, even with different SIS mixer devices. The quality of the RF and IF design is
confirmed by a sideband rejection ratio of about 15 dB, which is within the ALMA spec (>10dB ).
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.
In the far-infrared (FIR) / THz regime the angular (and often spectral) resolution of observing facilities is still very
restricted despite the fact that this frequency range has become of prime importance for modern astrophysics. ALMA
(Atacama Large Millimeter Array) with its superb sensitivity and angular resolution will only cover frequencies up to
about 1 THz, while the HIFI instrument for ESA'a Herschel Space Observatory will provide limited angular resolution
(10 to 30 arcsec) up to 2 THz. Observations of regions with star and planet formation require extremely high angular
resolution as well as frequency resolution in the full THz regime. In order to open these regions for high-resolution
astrophysics we present a study concept for a heterodyne space interferometer, ESPRIT (Exploratory Submm Space
Radio-Interferometric Telescope). This mission will cover the Terahertz regime inaccessible from the ground and outside
the operating range of the James Webb Space Telescope (JWST).
We report on developments of submillimeter heterodyne arrays for high resolution spectroscopy with APEX. Shortly, we will operate
state-of-the-art instruments in all major atmospheric windows accessible from Llano de Chajnantor. CHAMP+, a dual-color 2×7 element heterodyne array for operation in the 450 μm and 350 μm atmospheric windows is in operation since late 2007. With its
state-of-the-art SIS detectors and wide tunable local oscillators, its cold optics with single sideband filters and with 3 GHz of processed IF bandwidth per pixel, CHAMP+ does provide outstanding observing capabilities. The Large APEX sub-Millimeter Array (LAsMA) is in the final design phase, with an installation goal in 2009. The receiver will operate 7 and 19 pixels in the lower submillimeter windows, 285-375 GHz and 385-520 GHz, respectively. The front-ends are served by an array of digital wideband Fast Fourier Transform spectrometers currently processing up to 32×1.5 (optionally 1.8) GHz of bandwidth. For CHAMP+, we process 2.8 GHz of instantaneous bandwidth (in 16.4 k channels) for each of the 14 pixels.
The Atacama Large Millimetre Array will be a single research instrument composed of up to 50 high precision antennas,
located at the Chajnantor plain in the district of San Pedro de Atacama, 5000m above sea level. Each ALMA telescope
will contain 10 frequency channels/bands, ranging from 30 to 950GHz. Radiation from the secondary reflector is
collected to the receivers of each wavelength channel through their accompanying front end optics. We present a full
electromagnetic treatment of the front end optics for band 5 (163 - 211 GHz) and band 9 (602 - 720 GHz). A full quasi
optical and physical optics analysis of the band 5 front end optics, using the antenna analysis tool, GRASP9  is
presented. Potential optimisation for the system is presented, namely a reflector edge taper and a comparison of two
surface geometries. A similar analysis of the band 9 system is presented. Full electromagnetic simulations are compared
with cold beam pattern measurements made at the Space Research Organisation of the Netherlands [2, 3]. Analysis of the
effect of the polarizing grid is presented, with suggested modifications to improve cross polar levels.
CHAMP+, a dual-color 2 × 7 element heterodyne array for operation in the 450 μm and 350 μm atmospheric windows is under development. The instrument, which is currently undergoing final evaluation in the laboratories, will be deployed for commissioning at the APEX telescope in August this year.
With its state-of-the-art SIS detectors and wide tunable local oscillators, its cold optics with SSB filters and with 2 GHz of usable IF bandwidth per pixel, CHAMP+ will provide unmatched observing capabilities for the APEX community. The optics allows for simultaneous observations in both colors. For both sub-arrays a hexagonal arrangement with closest feasible spacing of the pixels on sky (2×Θmb) was chosen, which, in scanning mode, will provide data sampled with half-beam spacing. The front-end is connected to a flexible autocorrelator array with a total bandwidth of 32 GHz and 32768 spectral channels, subdivided into 32 IF bands of 1 GHz and 1024 channels each.
The ALMA telescope will be an interferometer of 64 antennas, which will be situated in the Atacama desert in Chile. Each antenna will have receivers that cover the frequencies 30 GHz to 970 GHZ. This frequency range is divided into 10 frequency bands. All of these receiver bands are fitted on a cartridge and cooled, with bands 1 and 2 at 15K and the other 8 are SIS receivers at a temperature of 4K. Each band has a dual polarization receiver. The optics has been designed so that the maximum of the optics is cooled to minimize the noise temperature increase to the receivers.
The design of the optics will be shown for each frequency bands. Test results with the method of testing on a near field amplitude and phase measurement system will be given for the first 4 frequency bands to be used, which are bands 3 (84-116 GHz), 6 (211-275GHz), 7 (275-375 GHz and 9 (600-702 GHz). These measurements will be compared with physical optics calculations.
The Atacama Large Millimeter Array (ALMA), a joint project between Europe and the U.S. and at present in its design and development phase, is a major new ground based telescope facility for millimeter and submillimeter astronomy. Its huge collecting area (7000 m2), sensitive receivers and location at one of the driest sites on Earth will make it a unique instrument. We present preliminary design concepts for the overall receiver configuration. Optics and cryostat design concepts from OSO, OVRO, RAL, IRAM, NRAO and SRON and their main features are described.