SuperSpec is an integrated, on-chip spectrometer for millimeter and sub-millimeter astronomy. SuperSpec is demonstrating a proof-of-principle multi-beam spectrometer on the sky at the Large Millimeter Telescope (LMT) in Mexico covering the 200 - 300 GHz frequency range with moderate resolution (R ~ 270 - 290). The dual-polarization, three-pixel instrument will consist of 6 SuperSpec spectrometer chips. We present the design and characterization of the devices being used in the first SuperSpec demonstration along with lab testing of the instrument performance.
Far-infrared astronomy has advanced rapidly since its inception in the late 1950s, driven by a maturing technology base and an expanding community of researchers. This advancement has shown that observations at far-infrared wavelengths are important in nearly all areas of astrophysics, from the search for habitable planets and the origin of life to the earliest stages of galaxy assembly in the first few hundred million years of cosmic history. The combination of a still-developing portfolio of technologies, particularly in the field of detectors, and a widening ensemble of platforms within which these technologies can be deployed, means that far-infrared astronomy holds the potential for paradigm-shifting advances over the next decade. We examine the current and future far-infrared observing platforms, including ground-based, suborbital, and space-based facilities, and discuss the technology development pathways that will enable and enhance these platforms to best address the challenges facing far-infrared astronomy in the 21st century.
Future generations of far-infrared (FIR) telescopes will need detectors with noise-equivalent powers on the order of 5x10-20 W/Hz1/2 in order to be photon background limited by astrophysical sources. One such mission concept in development is the Galaxy Evolution Probe (GEP), which will characterize galaxy formation and evolution from z=0 to beyond z=4. Kinetic inductance detectors (KIDs) have been baselined for the GEP for spectroscopy and imaging science between 10 μm and 400 μm due to their intrinsic frequency multiplexability and simple readout schemes. We focus on quasiparticle recombination times as a strategy for increasing detector responsivities to move towards the NEP requirements of the GEP. We present a new model for quantifying time constants from the responses of detectors to pulses of light, and test this model on a 40 nm thick ¼ λ Al coplanar waveguide KID. We intend to use this measurement scheme to quantify the dependence of the quasiparticle recombination time on Al thickness.
KEYWORDS: Mirrors, Amplifiers, Thermal modeling, Space telescopes, Sensors, Telescopes, Beryllium, Space operations, James Webb Space Telescope, Galaxy evolution
The Galaxy Evolution Probe (GEP) is a proposed far infrared-optimized observatory designed for zodiacal-light-limited imaging and spectroscopy in the 10 to 250 micron band. The GEP telescopes and instruments are planned to be actively cooled with the system in a sun-earth L2 halo orbit. A detailed description of the GEP mission concept is documented in [1]. Crucial to the scientific performance of GEP is the thermal architecture; it must support a range of cryogenic elements, ranging from the full telescope optical assembly at around 4 K to the far-IR focal planes consisting of kinetic inductance detector (KID) arrays cooled to 100 mK. Given the mass operating at these low temperatures, the thermal system is one of the main drivers of mission cost and complexity. We present a solution to the GEP thermal design that is realizable within a probe-class envelope. The baseline system utilizes a multi-stage adiabatic demagnetization refrigerator (ADR) for the 100mK base; the ADR system also provides an intercept at 1K. ADR systems similar to that in our design have flown, and among sub-K options, ADRs offer high Carnot efficiency. The ADR rejects heat to a hybrid Joule Thompson (JT) and Stirling or PT Cryocooler with a lowtemperature stage at 4 K as well as an intercept at 20 K. These coolers are also mature systems with flight heritage on most subcomponents.
The Galaxy Evolution Probe (GEP) is a concept for a mid and far-infrared space observatory designed to survey sky for star-forming galaxies from redshifts of z = 0 to beyond z = 4. Furthering our knowledge of galaxy formation requires uniform surveys of star-forming galaxies over a large range of redshifts and environments to accurately describe star formation, supermassive black hole growth, and interactions between these processes in galaxies. The GEP design includes a 2 m diameter SiC telescope actively cooled to 4 K and two instruments: (1) An imager to detect star-forming galaxies and measure their redshifts photometrically using emission features of polycyclic aromatic hydrocarbons. It will cover wavelengths from 10 to 400 μm, with 23 spectral resolution R = 8 filter-defined bands from 10 to 95 μm and five R = 3.5 bands from 95 to 400 μm. (2) A 24 – 193 μm, R = 200 dispersive spectrometer for redshift confirmation, identification of active galactic nuclei, and interstellar astrophysics using atomic fine-structure lines. The GEP will observe from a Sun-Earth L2 orbit, with a design lifetime of four years, devoted first to galaxy surveys with the imager and second to follow-up spectroscopy. The focal planes of the imager and the spectrometer will utilize KIDs, with the spectrometer comprised of four slit-coupled diffraction gratings feeding the KIDs. Cooling for the telescope, optics, and KID amplifiers will be provided by solar-powered cryocoolers, with a multi-stage adiabatic demagnetization refrigerator providing 100 mK cooling for the KIDs.
SuperSpec is an on-chip filter-bank spectrometer designed for wideband moderate-resolution spectroscopy at millimeter and submillimeter wavelengths. Employing TiN kinetic inductance detectors, the device has demonstrated noise performance suitable for photon noise limited ground-based observations at excellent millimeter-wave observing sites. In these proceedings we present a demonstration instrument featuring six independent single-polarization SuperSpec chips, covering 190-310 GHz with 300 channels. We summarize spectrometer performance, describe the cryostat and optical coupling, and present the readout and telescope control system. In an initial deployment to the Large Millimeter Telescope, we plan to observe submillimeter galaxies in [CII] emission at redshifts 5 < z < 9 and CO emission from lower-redshift galaxies. Real on-sky performance will inform the design of the next generation of instruments using large numbers of SuperSpec devices, which could include multi-object spectrometers or line intensity mapping experiments that target [CII] during the Epoch of Reionization.
SuperSpec is a new technology for millimeter and submillimeter spectroscopy. It is an on-chip spectrometer being developed for multi-object, moderate resolution (R = ~300), large bandwidth survey spectroscopy of high-redshift galaxies for the 1 mm atmospheric window. SuperSpec targets the CO ladder in the redshift range of z = 0 to 4, the [CII] 158 um line from z = 5 to 9, and the [NII] 205 um line from z = 4-7. All together these lines offer complete redshift coverage from z = 0 to 9. SuperSpec employs a novel architecture in which detectors are coupled to a series of resonant filters along a single microwave feedline instead of using dispersive optics. This construction allows for the creation of a full spectrometer occupying only 20 cm squared of silicon, a reduction in size of several orders of magnitude when compared to standard grating spectrometers. This small profile enables the production of future multi-object spectroscopic instruments required as the millimeter-wave spectroscopy field matures.
SuperSpec uses a lens-coupled antenna to deliver astrophysical radiation to a microstrip transmission line. The radiation then propagates down this transmission line where upon proximity coupled half wavelength microstrip resonators pick off specific frequencies of radiation. Careful tuning of the proximity of the resonators to the feedline dials in the desired resolving power of the SuperSpec filterbank by tuning the coupling quality factor. The half wavelength resonators are then in turn coupled to the inductive meander of kinetic inductance detectors (KIDs), which serve as the power detectors for the SuperSpec filterbank. Each SuperSpec filter bank contains hundreds of titanium nitride TiN KIDs and the natural multiplexibility of these detectors allow for readout of the large numbers of required detectors. The unique coupling scheme employed by SuperSpec allows for the creation of incredibly low volume (2.6 cubic microns), high responsivity, TiN KIDs. Since responsivity is proportional to the inverse of quasiparticle-occupied volume, this allows SuperSpec to reach the low NEPs required by moderate resolution spectroscopy to be photon limited from the best ground-based observing sites.
We will present the latest results from SuperSpec devices. In particular, detector NEPs, measured filter bank efficiency (including transmission line losses), and spectral profiles for a full ~ 300-channel filterbank. Finally, we will report on our system end to end efficiency and total system NEP.
SuperSpec is an integrated, on-chip spectrometer for millimeter and sub-millimeter astronomy. We report the approach, design optimization, and partial characterization of a 300 channel filterbank covering the 185 to 315 GHz frequency band that targets a resolving power R ~ 310, and fits on a 3.5×5.5 cm chip. SuperSpec uses a lens and broadband antenna to couple radiation into a niobium microstrip that feeds a bank of niobium microstrip half-wave resonators for frequency selectivity. Each half-wave resonator is coupled to the inductor of a titanium nitride lumped-element kinetic inductance detector (LEKID) that detects the incident radiation. The device was designed for use in a demonstration instrument at the Large Millimeter Telescope (LMT).
SuperSpec is a new spectrometer-on-a-chip technology for submm/mm-wave spectroscopy. SuperSpec stands out from other direct-detection submm spectrometer technologies in that the detectors are coupled to a series of resonant filters along a single microwave feedline instead of using dispersive optics. SuperSpec makes use of kinetic inductance detectors (KIDs) to detect radiation in this filter bank. The small profile of this design makes SuperSpec a natural choice to produce a multi-object spectrometer for tomographic mapping or galaxy redshift surveys. We have recently fabricated a device that is a 50 channel subset of a full 280 channel filter bank, which would cover the 190 - 310 GHz range at R = 275. Analysis of the data from this device informs us of the potential design modifications to enable a high-yield background-limited SuperSpec spectrometer. The results indicate that this subset filter bank can scale up to a full filter bank with only a few collisions in readout space and less than 20% variation in responsivity for the detectors. Additionally, the characterization of this and other prototype devices suggests that the noise performance is limited by generation-recombination noise. Finally, we find that the detectors are sufficiently sensitive for ground-based spectroscopy at R = 100, appropriate for tomographic mapping experiments. Further modifications are required to reach the background limit for R = 400, ideal for spectroscopy of individual galaxies.
To characterize further the cosmic star formation history at high redshifts, a large-area survey by a cryogenic 4-6 meter class telescope with a focal plane populated by tens of thousands of far-infrared (FIR, 30-300 μm) detectors with broadband detector noise equivalent powers (NEPs) on the order of 3×10-9 W/√ Hz is needed. Ideal detectors for such a surveyor do not yet exist. As a demonstration of one technique for approaching the ultra-low NEPs required by this surveyor, we present the design of an array of 96 350 µm KIDs that utilize phonon recycling to boost responsivity. Our KID array is fabricated with TiN deposited on a silicon-on-insulator (SOI) wafer, which is a 2 μm thick layer of silicon bonded to a thicker slab of silicon by a thin oxide layer. The backside thick slab is etched away underneath the absorbers so that the inductors are suspended on just the 2 μm membrane. The intent is that quasiparticle recombination phonons are trapped in the thin membrane, thereby increasing their likelihood of being re-absorbed by the KID to break additional Cooper pairs and boost responsivity. We also present a Monte-Carlo simulation that predicts the amount of signal boost expected from phonon recycling given different detector geometries and illumination strategies. For our current array geometry, the simulation predicts a measurable 50% boost in responsivity.
We present the design and characterization of low-volume, lumped-element aluminum kinetic inductance de-
tectors for sensitive far-infrared astronomy observations. The lumped-element kinetic inductance detectors are
comprised of meandered inductors that serve as radiation absorbers in parallel with interdigitated capacitors,
forming high quality factor resonators. Low inductor volumes lead to low noise equivalent powers by raising
quasiparticles densities, and hence responsivities, with respect to larger volumes. Low volumes are achieved
with thin (20 nm), narrow (150 nm) inductors. The interdigitated capacitor architecture is designed to mitigate
two-level system noise by lowering electric fields in the silicon substrate. Resonance frequencies are in the range
of 190 to 500 MHz, with measured internal quality factors in excess of 1 x 105. In a prior incarnation, a titanium
nitride layer on top of the aluminum served as a protective layer, but complicated the superconducting proper-
ties. These results were reported previously. In the current incarnation, the aluminum layer is left bare with
no titanium nitride over-layer. The results for these bare aluminum devices include a yield of 88%, frequency
responsivity of 109 W-1, and noise equivalent power of 1 x 10-17 W Hz-1/2 for a 350μm array. There is no
evidence for 1=f noise down to at least 200 mHz. The sensitivity is currently limited by white noise, very likely
from stray light in the testbed; for this detector design, sensitivities limited by generation-recombination noise
in a lower-background environment should be several orders of magnitude lower.
The Multiwavelength Sub/millimeter Inductance Camera (MUSIC) is a four-band photometric imaging camera operating from the Caltech Submillimeter Observatory (CSO). MUSIC is designed to utilize 2304 microwave kinetic inductance detectors (MKIDs), with 576 MKIDs for each observing band centered on 150, 230, 290, and 350 GHz. MUSIC’s field of view (FOV) is 14′ square, and the point-spread functions (PSFs) in the four observing bands have 45′′, 31′′, 25′′, and 22′′ full-widths at half maximum (FWHM). The camera was installed in April 2012 with 25% of its nominal detector count in each band, and has subsequently completed three short sets of engineering observations and one longer duration set of early science observations. Recent results from on-sky characterization of the instrument during these observing runs are presented, including achieved map- based sensitivities from deep integrations, along with results from lab-based measurements made during the same period. In addition, recent upgrades to MUSIC, which are expected to significantly improve the sensitivity of the camera, are described.
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. CCAT's 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.
Low-loss lenses are required for submillimeter astronomical applications, such as instrumentation for CCAT, a 25 m diameter telescope to be built at an elevation of 18,400 ft in Chile. Silicon is a leading candidate for dielectric lenses due to its low transmission loss and high index of refraction; however, the latter can lead to large reflection losses. Additionally, large diameter lenses (up to 40 cm), with substantial curvature present a challenge for fabrication of antireflection coatings. Three anti-reflection coatings are considered: a deposited dielectric coating of Parylene C, fine mesh structures cut with a dicing saw, and thin etched silicon layers (fabricated with deep reactive ion etching) for bonding to lenses. Modeling, laboratory measurements, and practicalities of fabrication for the three coatings are presented and compared. Measurements of the Parylene C anti-reflection coating were found to be consistent with previous studies and can be expected to result in a 6% transmission loss for each interface from 0.787 to 0.908 THz. The thin etched silicon layers and fine mesh structure anti-reflection coatings were designed and fabricated on test silicon wafers and found to have reflection losses less than 1% at each interface from 0.787 to 0.908 THz. The thin etched silicon layers are our preferred method because of high transmission efficiency while having an intrinsically faster fabrication time than fine structures cut with dicing saws, though much work remains to adapt the etched approach to curved surfaces and optics < 4" in diameter unlike the diced coatings.
We present the status of MUSIC, the MUltiwavelength Sub/millimeter Inductance Camera, a new instrument for the
Caltech Submillimeter Observatory. MUSIC is designed to have a 14', diffraction-limited field-of-view instrumented
with 2304 detectors in 576 spatial pixels and four spectral bands at 0.87, 1.04, 1.33, and 1.98 mm. MUSIC will be used
to study dusty star-forming galaxies, galaxy clusters via the Sunyaev-Zeldovich effect, and star formation in our own and
nearby galaxies. MUSIC uses broadband superconducting phased-array slot-dipole antennas to form beams, lumpedelement
on-chip bandpass filters to define spectral bands, and microwave kinetic inductance detectors to sense incoming
light. The focal plane is fabricated in 8 tiles consisting of 72 spatial pixels each. It is coupled to the telescope via an
ambient-temperature ellipsoidal mirror and a cold reimaging lens. A cold Lyot stop sits at the image of the primary
mirror formed by the ellipsoidal mirror. Dielectric and metal-mesh filters are used to block thermal infrared and out-ofband
radiation. The instrument uses a pulse tube cooler and 3He/ 3He/4He closed-cycle cooler to cool the focal plane to
below 250 mK. A multilayer shield attenuates Earth's magnetic field. Each focal plane tile is read out by a single pair of
coaxes and a HEMT amplifier. The readout system consists of 16 copies of custom-designed ADC/DAC and IF boards
coupled to the CASPER ROACH platform. We focus on recent updates on the instrument design and results from the
commissioning of the full camera in 2012.
As a proof-of-concept, we have constructed and tested a cryogenic polarimeter in the laboratory as a prototype
for the MUSIC instrument (Multiwavelength Sub/millimeter Kinetic Inductance Camera). The POLOCAM
instrument consists of a rotating cryogenic polarization modulator (sapphire half-waveplate) and polarization
analyzer (lithographed copper polarizers deposited on a thin film) placed into the optical path at the Lyot stop
(4K cold pupil stop) in a cryogenic dewar. We present an overview of the project, design and performance
results of the POLOCAM instrument (including polarization efficiencies and instrumental polarization), as well
as future application to the MUSIC-POL instrument.
We are developing the Background-Limited Infrared-Submillimeter Spectrograph (BLISS) for SPICA to provide
a breakthrough capability for far-IR survey spectroscopy. SPICAs large cold aperture allows mid-IR to submm
observations which are limited only by the natural backgrounds, and BLISS is designed to operate near this
fundamental limit. BLISS-SPICA is 6 orders of magnitude faster than the spectrometers on Herschel and
SOFIA in obtaining full-band spectra. It enables spectroscopy of dust-obscured galaxies at all epochs back to
the rst billion years after the Big Bang (redshift 6), and study of all stages of planet formation in circumstellar
disks.
BLISS covers 35 - 433 microns range in ve or six wavelength bands, and couples two 2 sky positions simultaneously.
The instrument is cooled to 50 mK for optimal sensitivity with an on-board refrigerators. The detector
package is 4224 silicon-nitride micro-mesh leg-isolated bolometers with superconducting transition-edge-sensed
(TES) thermistors, read out with a cryogenic time-domain multiplexer. All technical elements of BLISS have
heritage in mature scientic instruments, and many have own. We report on our design study in which we are
optimizing performance while accommodating SPICAs constraints, including the stringent cryogenic mass budget.
In particular, we present our progress in the optical design and waveguide spectrometer prototyping. A
companion paper in Conference 7741 (Beyer et al.) discusses in greater detail the progress in the BLISS TES
bolometer development.
C. Darren Dowell, Michael Pohlen, Chris Pearson, Matt Griffin, Tanya Lim, George Bendo, Dominique Benielli, James Bock, Pierre Chanial, Dave Clements, Luca Conversi, Marc Ferlet, Trevor Fulton, Rene Gastaud, Jason Glenn, Tim Grundy, Steve Guest, Ken King, Sarah Leeks, Louis Levenson, Nanyao Lu, Huw Morris, Hien Nguyen, Brian O'Halloran, Seb Oliver, Pasquale Panuzzo, Andreas Papageorgiou, Edward Polehampton, Dimitra Rigopoulou, Helene Roussel, Nicola Schneider, Bernhard Schulz, Arnold Schwartz, David Shupe, Bruce Sibthorpe, Sunil Sidher, Anthony Smith, Bruce Swinyard, Markos Trichas, Ivan Valtchanov, Adam Woodcraft, C. Kevin Xu, Lijun Zhang
We describe the current state of the ground segment of Herschel-SPIRE photometer data processing, approximately
one year into the mission. The SPIRE photometer operates in two modes: scan mapping and chopped
point source photometry. For each mode, the basic analysis pipeline - which follows in reverse the effects from
the incidence of light on the telescope to the storage of samples from the detector electronics - is essentially
the same as described pre-launch. However, the calibration parameters and detailed numerical algorithms have
advanced due to the availability of commissioning and early science observations, resulting in reliable pipelines
which produce accurate and sensitive photometry and maps at 250, 350, and 500 μm with minimal residual
artifacts. We discuss some detailed aspects of the pipelines on the topics of: detection of cosmic ray glitches,
linearization of detector response, correction for focal plane temperature drift, subtraction of detector baselines
(offsets), absolute calibration, and basic map making. Several of these topics are still under study with the
promise of future enhancements to the pipelines.
We will present the design and implementation, along with calculations and some measurements of the performance,
of the room-temperature and cryogenic optics for MUSIC, a new (sub)millimeter camera we are
developing for the Caltech Submm Observatory (CSO). The design consists of two focusing elements in addition
to the CSO primary and secondary mirrors: a warm off-axis elliptical mirror and a cryogenic (4K) lens. These
optics will provide a 14 arcmin field of view that is diffraction limited in all four of the MUSIC observing bands
(2.00, 1.33, 1.02, and 0.86 mm). A cold (4K) Lyot stop will be used to define the primary mirror illumination,
which will be maximized while keeping spillover at the sub 1% level. The MUSIC focal plane will be populated
with broadband phased antenna arrays that efficiently couple to factor of (see manuscript) 3 in bandwidth,1, 2 and each pixel on
the focal plane will be read out via a set of four lumped element filters that define the MUSIC observing bands
(i.e., each pixel on the focal plane simultaneously observes in all four bands). Finally, a series of dielectric and
metal-mesh low pass filters have been implemented to reduce the optical power load on the MUSIC cryogenic
stages to a quasi-negligible level while maintaining good transmission in-band.
MUSIC (the Multiwavelength Submillimeter kinetic Inductance Camera) is an instrument being developed for
the Caltech Submillimeter Observatory by Caltech, JPL, the University of Colorado, and UCSB. MUSIC uses
microwave kinetic inductance detectors (MKIDs) - superconducting micro-resonators - as photon detectors. The
readout is almost entirely at room temperature and is highly multiplexed. MUSIC will have 576 spatial pixels
in four bands at 850, 1100, 1300 and 2000 microns. MUSIC is scheduled for deployment at the CSO in the
winter of 2010/2011. We present an overview of the camera design and readout and describe the current status
of the instrument and some results from the highly successful May/June 2010 observing run at the CSO with the
prototype camera, which verified the performance of the complete system (optics, antennas/filters, resonators,
and readout) and produced the first simultaneous 3-color observations with any MKID camera.
We present the results of the latest multicolor Microwave Kinetic Inductance Detector (MKID) focal plane arrays
in the submillimeter. The new detectors on the arrays are superconducting resonators which combine a coplanar
waveguide section with an interdigitated capacitor, or IDC. To avoid out-of-band pickup by the capacitor, a
stepped-impedance filter is used to prevent radiation from reaching the absorptive aluminum section of the
resonator. These arrays are tested in the preliminary demonstration instrument, DemoCam, a precursor to the
Multicolor Submillimeter Inductance Camera, MUSIC. We present laboratory results of the responsivity to light
both in the laboratory and at the Caltech Submillimeter Observatory. We assess the performance of the detectors
in filtering out-of-band radiation, and find the level of excess load and its effect on detector performance. We
also look at the array design characteristics, and the implications for the optimization of sensitivities expected
by MUSIC.
MUSIC (Multicolor Submillimeter kinetic Inductance Camera) is a new facility instrument for the Caltech Submillimeter
Observatory (Mauna Kea, Hawaii) developed as a collaborative effect of Caltech, JPL, the University
of Colorado at Boulder and UC Santa Barbara, and is due for initial commissioning in early 2011. MUSIC utilizes
a new class of superconducting photon detectors known as microwave kinetic inductance detectors (MKIDs), an
emergent technology that offers considerable advantages over current types of detectors for submillimeter and
millimeter direct detection. MUSIC will operate a focal plane of 576 spatial pixels, where each pixel is a slot line
antenna coupled to multiple detectors through on-chip, lumped-element filters, allowing simultaneously imaging
in four bands at 0.86, 1.02, 1.33 and 2.00 mm.
The MUSIC instrument is designed for closed-cycle operation, combining a pulse tube cooler with a two-stage
Helium-3 adsorption refrigerator, providing a focal plane temperature of 0.25 K with intermediate temperature
stages at approximately 50, 4 and 0.4 K for buffering heat loads and heat sinking of optical filters. Detector
readout is achieved using semi-rigid coaxial cables from room temperature to the focal plane, with cryogenic
HEMT amplifiers operating at 4 K. Several hundred detectors may be multiplexed in frequency space through
one signal line and amplifier.
This paper discusses the design of the instrument cryogenic hardware, including a number of features unique to
the implementation of superconducting detectors. Predicted performance data for the instrument system will
also be presented and discussed.
Detectors employing superconducting microwave kinetic inductance detectors (MKIDs) can be read out by
measuring changes in either the resonator frequency or dissipation. We will discuss the pros and cons of both
methods, in particular, the readout method strategies being explored for the Multiwavelength Sub/millimeter
Inductance Camera (MUSIC) to be commissioned at the CSO in 2010. As predicted theoretically and observed
experimentally, the frequency responsivity is larger than the dissipation responsivity, by a factor of 2-4 under
typical conditions. In the absence of any other noise contributions, it should be easier to overcome amplifier
noise by simply using frequency readout. The resonators, however, exhibit excess frequency noise which has been
ascribed to a surface distribution of two-level fluctuators sensitive to specific device geometries and fabrication
techniques. Impressive dark noise performance has been achieved using modified resonator geometries employing
interdigitated capacitors (IDCs). To date, our noise measurement and modeling efforts have assumed an onresonance
readout, with the carrier power set well below the nonlinear regime. Several experimental indicators
suggested to us that the optimal readout technique may in fact require a higher readout power, with the carrier
tuned somewhat off resonance, and that a careful systematic study of the optimal readout conditions was needed.
We will present the results of such a study, and discuss the optimum readout conditions as well as the performance
that can be achieved relative to BLIP.
KEYWORDS: Field programmable gate arrays, Resonators, Interference (communication), Field effect transistors, Electronics, Signal processing, Amplifiers, Signal to noise ratio, Clocks, Microwave radiation
This paper will present the design, implementation, performance analysis of an open source readout system
for arrays of microwave kinetic inductance detectors (MKID) for mm/submm astronomy. The readout system
will perform frequency domain multiplexed real-time complex microwave transmission measurements in order
to monitor the instantaneous resonance frequency and dissipation of superconducting microresonators. Each
readout unit will be able to cover up to 550 MHz bandwidth and readout 256 complex frequency channels
simultaneously. The digital electronics include the customized DAC, ADC, IF system and the FPGA based
signal processing hardware developed by CASPER group.1-7 The entire system is open sourced, and can be
customized to meet challenging requirement in many applications: e.g. MKID, MSQUID etc.
We report measurements of the fluctuations in atmospheric emission (atmospheric noise) above Mauna Kea
recorded with Bolocam at 143 GHz. These data were collected in November and December of 2003 with Bolocam
mounted on the Caltech Submillimeter Observatory (CSO), and span approximately 40 nights. Below ≃ 0.5 Hz,
the data time-streams are dominated by the f-δ atmospheric noise in all observing conditions. We were able to
successfully model the atmospheric fluctuations using a Kolmogorov-Taylor turbulence model for a thin wind-driven
screen in approximately half of our data. Based on this modeling, we developed several algorithms to
remove the atmospheric noise, and the best results were achieved when we described the fluctuations using a
low-order polynomial in detector position over the 8 arcminute focal plane. However, even with these algorithms,
we were not able to reach photon-background-limited instrument photometer (BLIP) performance at frequencies
below ≃ 0.5 Hz in any observing conditions. Therefore, we conclude that BLIP performance is not possible from
the CSO below ≃ 0.5 Hz for broadband 150 GHz receivers with subtraction of a spatial atmospheric template
on scales of several arcminutes.
Z-Spec is a cryogenic, broadband, millimeter-wave grating spectrometer. It is capable of obtaining many
spectral lines simultaneously because of its unprecedented broad bandwidth (185-305GHz). The bandpass covers the
1mm atmospheric transmission window with a resolving power of 250-400. Z-Spec uses 160 silicon nitride micromesh
bolometers cooled down to less than 100mK for background-limited performance. The unique capability of Z-Spec to
detect multiple lines simultaneously allows us to obtain information efficiently on the physical and chemical conditions
of nearby Ultra-luminous Infrared Galaxies (ULIRGs) powered by starbursts or Active Galactic Nuclei. Here we report
on new millimeter-wave broadband data for ULIRGs acquired with Z-Spec and the noise performance and achieved
sensitivity in observations with the CSO. We found that during the observations the noise scales with the atmospheric
opacity and can be explained well by our sensitivity model, considering the photon noise originating from the sky and
the telescope, as well as the detector and electronics noise. The photon noise is found to dominate the total noise.
The MKID Camera is a millimeter/submillimeter instrument being built for astronomical observations from the Caltech
Submillimeter Observatory. It utilizes microwave kinetic inductance detectors, which are rapidly achieving near-BLIP
sensitivity for ground-based observations, and a software-defined radio readout technique for elegant multiplexing of a
large number of detectors. The Camera will have 592 pixels distributed over 16 tiles in the focal plane, with four colors
per pixel matched to the 750 μm, 850 μm, and 1.0 - 1.5 mm (split in two) atmospheric transmission windows. As a
precursor to building the full-up camera and to enable ongoing detector testing, we have built a DemoCam comprised of
a 16-pixel MKID array with which we have made preliminary astronomical observations. These observations
demonstrate the viability of MKIDs for submillimeter astronomy, provide insight into systematic design issues that must
be considered for MKID-based instruments, and they are the first astronomical observations with antenna-coupled
superconducting detectors. In this paper, we describe the basic systems and specifications of the MKID Camera, we
describe our DemoCam observations, and we comment on the status of submillimeter MKID sensitivities.
The Spectral and Photometric Imaging Receiver (SPIRE) is one of three scientific instruments on ESA's Herschel Space
Observatory. This long wavelength instrument covers 200 to 670μm with a three band photometric camera and a two
band imaging Fourier Transform Spectrometer (IFTS). Following first results reported in a previous paper, we discuss
the in-band optical performances of the flight model as measured extensively during several dedicated test campaigns.
Complementary to the experimentally probed spectral characteristics of the instrument detailed in an accompanying
paper (see L.D. Spencer et al., in these proceedings), attention is focused here on a set of standard but key tests aimed at
measuring the spatial response of the Photometer and Spectrometer end-to-end optical chain, including detector. Effects
of defocus as well as source size extent, in-band wavelength, and polarization are also investigated over respective
Photometer and Spectrometer field-of-views. Comparison with optical modelling, based on instrument design knowledge
and some of the internal component measured characteristics, is performed. Beyond the specific characterisation of each
effect, this allows estimating in each band where optical behaviour and detector behaviour respectively dominates and
also reconstructing some of the contributors to the instrument throughput. Based on this analysis, retrieved optical
performances are finally assessed against the related science-driven instrument requirements.
SPIRE, the Spectral and Photometric Imaging Receiver, is a submillimetre camera and spectrometer for Herschel. It
comprises a three-band camera operating at 250, 350 and 500 µm, and an imaging Fourier Transform Spectrometer
covering 194-672 μm. The photometer field of view is 4x8 arcmin., viewed simultaneously in the three bands. The FTS
has an approximately circular field of view of 2.6 arcmin. diameter and spectral resolution adjustable between 0.04 and 2
cm-1 ( λ/▵λ=20-1000 at 250 μm). Following successful testing in a dedicated facility designed to simulate the in-flight
operational conditions, SPIRE has been integrated in the Herschel spacecraft and is now undergoing system-level testing
prior to launch. The main design features of SPIRE are reviewed, the key results of instrument testing are outlined, and
a summary of the predicted in-flight performance is given.
We describe the on-board electronics chain and the on-ground data processing pipeline that will operate on data from the
Herschel-SPIRE photometer to produce calibrated astronomical products. Data from the three photometer arrays will be
conditioned and digitised by on-board electronics and sent to the ground with no further on-board data processing. On
the ground, the data pipeline will process the data from point source, jiggle-map, and scan-map observations in a fully
automatic manner, producing measured flux densities (for point source observations) or maps. It includes calculation of
the bolometer voltages from the raw telemetry, glitch removal, and corrections for various effects including time
constants associated with the detectors and electronics, electrical and optical crosstalk, detector temperature drifts, flatfielding,
and non-linear response of the bolometers to strong sources. Flux density calibration will be with respect to
standard astronomical sources with the planets Uranus and Neptune being adopted as the baseline primary standards.
The pipeline will compute estimated values of in-beam flux density for a standard flat νS(ν) source spectrum.
Five partners have currently joined a Consortium to develop the Cornell Caltech Atacama Telescope (CCAT.) Included
are Cornell University, the California Institute of Technology (Caltech), the University of Colorado at Boulder, the
United Kingdom as represented by the Astronomy Technology Centre (ATC), and Canada as represented by the
Universities of British Columbia and Waterloo. This consortium has continued work toward the design of the telescope
and instrumentation, pursued fund raising, and further developed the science case for CCAT. An Engineering Design
Phase is being planned for 2009-2011 with construction planned to begin shortly thereafter. CCAT continues as a wide
field (20 arc min) FOV telescope operating from a shortest wavelength of 200µ. Testing has continued near the summit
of Cerro Chajnantor in the Atacama Region of Chile above 5600 meters altitude and data indicates significantly lower
water vapor in the seeing column than measured at the ALMA site on the plateau below. Work over the past two years
has included research on manufacturing methods for optical segments, extensive study of mirror alignment sensing and
control techniques, additional concepts for major structures, and further development of instrumentation.
The Spectral and Photometric Imaging Receiver (SPIRE) is one of three scientific instruments on ESA's Herschel Space
Observatory. The instrument covers 200 to 670 μm with a three band photometric camera and a two band imaging
Fourier Transform Spectrometer (IFTS). In this paper we discuss the performance of the optics of the instrument as
determined during the pre-flight instrument testing to date. In particular we concentrate on the response of the
instrument to a point source, the comparison between the visible light alignment and the infrared alignment and the
effect of the optical performance on the overall instrument sensitivity. We compare the empirical performance of the
instrument optics to that expected from elementary diffraction theory.
Matthew Griffin, Alain Abergel, Peter Ade, Philippe André, Jean-Paul Baluteau, James Bock, Alberto Franceschini, Walter Gear, Jason Glenn, Douglas Griffin, Ken King, Emmanuel Lellouch, David Naylor, Göran Olofsson, Ismael Perez-Fournon, Michael Rowan-Robinson, Paolo Saraceno, Eric Sawyer, Alan Smith, Bruce Swinyard, Laurent Vigroux, Gillian Wright
SPIRE, the Spectral and Photometric Imaging Receiver, is a submillimetre camera and spectrometer for the European Space Agency's Herschel Space Observatory. It comprises a three-band imaging photometer operating at 250, 360 and 520 μm, and an imaging Fourier Transform Spectrometer (FTS) covering 200-670 μm. The detectors are arrays of feedhorn-coupled NTD spider-web bolometers cooled to 0.3 K. The photometer field of view of is 4 x 8 arcmin.,
observed simultaneously in the three spectral bands. The FTS has an approximately circular field of view with a diameter of 2.6 arcmin., and employs a dual-beam configuration with broad-band intensity beam dividers to provide high efficiency and separated output and input ports. The spectral resolution can be adjusted between 0.04 and 2 cm-1 (resolving power of 20-1000 at 250 μm). The flight instrument is currently undergoing integration and test. The design of SPIRE is described, and the expected scientific performance is summarised, based on modelling and flight instrument test results.
We report on the status of Z-Spec, including preliminary results of our first astronomical measurements. Z-Spec is a cryogenic, broadband, millimeter-wave grating spectrometer designed for molecular line surveys of galaxies, including carbon monoxide redshift measurements of high-redshift submillimeter sources. With an instantaneous bandwidth of 185-305 GHz, Z-Spec covers the entire 1 mm atmospheric transmission window with a resolving power of 200-400. The spectrometer employs the Waveguide Far-Infrared Spectrometer (WaFIRS) architecture, in which the light propagation is confined within a parallel-plate waveguide, resulting in a minimum mechanical envelope. Its array of 160 silicon-nitride micromesh bolometers is cooled to below 100 mK for background-limited performance. With its sensitivity, broad bandwidth, and compactness, Z-Spec serves as a prototype for a future far-IR spectrometer aboard a cold telescope in space. Z-Spec successfully demonstrated functionality with a partial array of detectors and warm electronics during a week-long engineering run at the Caltech Submillimeter Observatory in June, 2005. We describe the instrument performance evaluated at the telescope and in subsequent laboratory tests and compare these results with design specifications. Following several modifications we returned to the telescope in April, 2006. We present a preliminary astronomical spectrum and discuss our plans to improve sensitivity and throughput to achieve our ultimate science goals.
Bolocam is a millimetre-wave (1.1 and 2.1 mm) camera with an array of 119 bolometers. It has been commissioned at the Caltech Submillimeter Observatory in Hawaii and is now in routine operation. Here we give an overview of the instrument and the data reduction pipeline. We discuss models of the sensitivity of Bolocam in different observing modes and under different atmospheric conditions. We briefly discuss observations of star-forming Galactic molecular clouds, a blank field survey for sub-millimeter galaxies, preliminary results of a blank-field CMB secondary anisotropy survey and discuss observations of galaxy clusters using the Sunyaev-Zel'dovich effect.
We present the design, integration, and first ryogenic testing of our new broad-band millimeter-wave spectrometer, Z-Spec. Z-Spec uses a novel architecture called WaFIRS (Waveguide Far-IR Spectrometer), which employs a curved diffraction grating in a parallel-plate waveguide propagation medium. The instrument will provide a resolving power betwee 200 and 350 across an instantaneous bandwidth of 190-310 GHz, all packaged within a cryostat that is of order 1 meter in size. For background-limited astronomical observations in the 1mm terrestrial window, Z-Spec uses 160 silicon nitride micro-mesh bolometers and the detectors and waveguide grating are cooled to ~0.1 K. Our first cryogenic measurements at 225 GHz show resolving power greater than 200, and the end-to-end throughput is estimated to be greater than 30%, possibly as high as 40%. Z-Spec represents the first systematic approach to cosmological redshift measurement that is not based on optical or near-IR identifications. With its good sensitivity and large bandwidth, Z-Spec provides a new capability for millimeter-wave astrophysics. The instrument will be capable of measureing rotational carbon monoxide line emission from bright dusty galaxies at redshifts of up to 4, and the broad bandwidth insures that at least two lines will be simultaneously detected, providing an unambiguous redshift determination. In addition to Z-Spec's observations over the next 1-3 years, the WaFIRS spectrometer architecture makes an excellent candidate for mid-IR to millimeter-wave spectrometers on future space-borned and suborbital platforms such as SPICA and SAFIR. The concept is dramatically more compact and lightweight than conventional free-space grating spectrometers, and no mirrors or lenses are used in the instrument. After the progress report on Z-Spec we highlight this capability.
The discovery of galaxies beyond z~1 which emit the bulk of their luminosity at long wavelengths has demonstrated the need for high-sensitivity, broad-band spectroscopy in the far-IR/submm/mm bands. Because many of these sources are not detectable in the optical,
long-wavelength spectroscopy is key to measuring their redshifts and ISM conditions. The continuum source list will increase in the coming decade with new ground-based instruments (SCUBA2, Bolocam, MAMBO), and the surveys of HSO and SIRTF. Yet the planned spectroscopic capabilities lag behind, in part due to the difficulty in scaling existing IR spectrograph designs to longer wavelengths. To overcome these limitations, we are developing WaFIRS, a novel concept for long-wavelength spectroscopy which utilizes a parallel-plate waveguide and a curved diffraction grating. WaFIRS provides the large (~60%) instantaneous bandwidth and high throughput of a conventional grating system, but offers a dramatic reduction in volume and mass. WaFIRS requires no space overheads for extra optical
elements beyond the diffraction grating itself, and is two-dimensional because the propagation is confined between two parallel plates. Thus several modules could be stacked to multiplex either spatially or in different frequency bands. The size and mass savings provide opportunities for spectroscopy from space-borne observatories which would be impractical with traditional spectrographs. With background-limited detectors and a cooled 3.5 m telescope, the line sensitivity would be comparable to that of ALMA, with instantaneous broad-band coverage. We present the spectrometer concept, performance verification with a mm-wave prototype, and our progress toward a cryogenic astronomical instrument
This paper reviews the design, modeling, and testing of feedhorn arrays coupled to bolometric detector arrays being developed for the ESA Herschel Space Observatory's SPIRE instrument. SPIRE will incorporate five arrays of silicon nitride micromesh bolometers, in three broadband photometers and two Fourier-Transform spectrometers covering 200-700 μm, with a total of 326 feedhorn-coupled bolometers. The precision feedhorn arrays are formed by close-packing individually fabricated conical feedhorns, which terminate in waveguides and integrating cavities. The detector array is efficiently packaged by mounting it between a metallized silicon backshort array and the feedhorn array, which encloses the bolometers in precisely tuned integrating cavities. The absorption efficiency, bandwidth, and cross talk were first investigated with numerical simulations of the electromagnetic fields, and then measured for prototype arrays in a test facility. This discussion describes the design goals, simulations, fabrication, and measurements of optical efficiencies, spectral properties, beam shapes, and cross talk between bolometers.
Z-Spec is a broadband (195 - 310 GHz), direct-detection, millimeter-wave spectrometer with moderate resolution (R ~ 350) that we are building to observe CO rotational lines and atomic fine-structure lines in the recently discovered population of submillimeter galaxies. A large fraction of these sources cannot be identified optically and thus redshift determination is extremely difficult. The large instantaneous bandwidth of Z-Spec will allow measurement of redshifts up to z~4 via detection of two or more CO lines in a single spectrum. The spectrometer is based on a parallel-plate waveguide grating architecture that is substantially more compact than a conventional free-space grating system. The spectrometer and an array of 160 silicon nitride micromesh bolometers will be cooled to 100 mK to provide background-limited sensitivity. In addition to measuring the redshifts of sources discovered in submillimeter continuum surveys, Z-Spec will demonstrate a novel spectrometer concept well-suited for future far-infrared space missions.
We describe the design and performance of Bolocam, a 144-element, bolometric, millimeter-wave camera. Bolocam is currently in its commissioning stage at the Caltech Submillimeter Observatory. We compare the instrument performance measured at the telescope with a detailed sensitivity model, discuss the factors limiting the current sensitivity, and describe our plans for future improvements intended to increase the mapping speed.
We are developing arrays of bolometers based on silicon nitride micromesh absorbers for the Spectral & Photometric Imaging Receiver (SPIRE) on the Far Infra-Red and Submillimeter Space Telescope (FIRST). The bolometers are coupled to a close-packed array of 1 f(lambda) feedhorns which views the primary mirror through a cooled aperture stop. Feedhorn-coupled bolometers minimize the detector area and throughput and have good optical efficiency. A 1 f(lambda) feedhorn array provides, higher mapping speed than a 2 f(lambda) feedhorn array and reduces the number of jitters required to produce a fully sampled map, but at the cost of more detectors. Individual silicon nitride micromesh bolometers are already able to meet the performance requirements of SPIRE. In parallel we are developing transition-edge detectors read out by SQUID current amplifier. The relatively large cooling power available at 300 mK enables the array to be coupled to a cold SQUID multiplexer, creating a monolithic fully multiplexed array and making large format arrays possible for SPIRE.
We describe the design of Bolocam, a bolometric camera for millimeter-wave observations at the Caltech Submillimeter Observatory. Bolocam will have 144 diffraction-limited detectors operating at 300 mK, an 8 arcminute field of view, and a sky noise limited NEFD of approximately 35 mJy Hz-1/2 per pixel at (lambda) equals 1.4 mm. Observations will be possible at one of (lambda) equals 1.1., 1.4, or 2.1 mm per observing run. The detector array consists of sensitive NTD Ge thermistors bonded to silicon nitride micromesh absorbers patterned on a single wafer of silicon. This is a new technology in millimeter-wave detector array construction. To increase detector packing density, the feed horns will be spaced by 1.26 f(lambda) (at (lambda) equals 1.4 mm), rather than the conventional 2 f(lambda) . DC stable read out electronics will enable on-the-fly mapping and drift scanning. We will use Bolocam to map Galactic dust emission, to search for protogalaxies, and to observe the Sunyaev- Zel'dovich effect toward galaxy clusters.
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