The Stratospheric Observatory for Infrared Astronomy (SOFIA) is the world’s largest airborne observatory, featuring a
2.5 meter effective aperture telescope housed in the aft section of a Boeing 747SP aircraft. SOFIA’s current instrument
suite includes: FORCAST (Faint Object InfraRed CAmera for the SOFIA Telescope), a 5-40 μm dual band
imager/grism spectrometer developed at Cornell University; HIPO (High-speed Imaging Photometer for Occultations), a
0.3-1.1μm imager built by Lowell Observatory; GREAT (German Receiver for Astronomy at Terahertz Frequencies), a
multichannel heterodyne spectrometer from 60-240 μm, developed by a consortium led by the Max Planck Institute for
Radio Astronomy; FLITECAM (First Light Infrared Test Experiment CAMera), a 1-5 μm wide-field imager/grism
spectrometer developed at UCLA; FIFI-LS (Far-Infrared Field-Imaging Line Spectrometer), a 42-200 μm IFU grating
spectrograph completed by University Stuttgart; and EXES (Echelon-Cross-Echelle Spectrograph), a 5-28 μm highresolution
spectrometer designed at the University of Texas and being completed by UC Davis and NASA Ames
Research Center. HAWC+ (High-resolution Airborne Wideband Camera) is a 50-240 μm imager that was originally
developed at the University of Chicago as a first-generation instrument (HAWC), and is being upgraded at JPL to add
polarimetry and new detectors developed at Goddard Space Flight Center (GSFC). SOFIA will continually update its
instrument suite with new instrumentation, technology demonstration experiments and upgrades to the existing
instrument suite. This paper details the current instrument capabilities and status, as well as the plans for future
The Stratospheric Observatory for Infrared Astronomy (SOFIA) is an airborne observatory, carrying a 2.5 m telescope onboard a heavily modified Boeing 747SP aircraft. SOFIA is optimized for operation at infrared wavelengths, much of which is obscured for ground-based observatories by atmospheric water vapor. The SOFIA science instrument complement consists of seven instruments: FORCAST (Faint Object InfraRed CAmera for the SOFIA Telescope), GREAT (German Receiver for Astronomy at Terahertz Frequencies), HIPO (High-speed Imaging Photometer for Occultations), FLITECAM (First Light Infrared Test Experiment CAMera), FIFI-LS (Far-Infrared Field-Imaging Line Spectrometer), EXES (Echelon-Cross-Echelle Spectrograph), and HAWC (High-resolution Airborne Wideband Camera). FORCAST is a 5–40 μm imager with grism spectroscopy, developed at Cornell University. GREAT is a heterodyne spectrometer providing high-resolution spectroscopy in several bands from 60–240 μm, developed at the Max Planck Institute for Radio Astronomy. HIPO is a 0.3–1.1 μm imager, developed at Lowell Observatory. FLITECAM is a 1–5 μm wide-field imager with grism spectroscopy, developed at UCLA. FIFI-LS is a 42–210 μm integral field imaging grating spectrometer, developed at the University of Stuttgart. EXES is a 5–28 μm high-resolution spectrograph, developed at UC Davis and NASA ARC. HAWC is a 50–240 μm imager, developed at the University of Chicago, and undergoing an upgrade at JPL to add polarimetry capability and substantially larger GSFC detectors. We describe the capabilities, performance, and status of each instrument, highlighting science results obtained using FORCAST, GREAT, and HIPO during SOFIA Early Science observations conducted in 2011.
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 describe our ongoing project to build a far-infrared polarimeter for the HAWC instrument on SOFIA. Far-IR
polarimetry reveals unique information about magnetic fields in dusty molecular clouds and is an important
tool for understanding star formation and cloud evolution. SOFIA provides flexible access to the infrared as
well as good sensitivity to and angular resolution of continuum emission from molecular clouds. We are making
progress toward outfitting HAWC, a first-generation SOFIA camera, with a four-band polarimeter covering 50 to
220 microns wavelength. We have chosen a conservative design which uses quartz half-wave plates continuously
rotating at ~0.5 Hz, ball bearing suspensions, fixed wire-grid polarizers, and cryogenic motors. Design challenges
are to fit the polarimeter into a volume that did not originally envision one, to minimize the heating of the
cryogenic optics, and to produce negligible interference in the detector system. Here we describe the performance
of the polarimeter measured at cryogenic temperature as well as the basic method we intend for data analysis.
We are on track for delivering this instrument early in the operating lifetime of SOFIA.
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.
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
Proc. SPIE. 7741, Millimeter, Submillimeter, and Far-Infrared Detectors and Instrumentation for Astronomy V
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.<sup>1-7</sup> The entire system is open sourced, and can be
customized to meet challenging requirement in many applications: e.g. MKID, MSQUID etc.
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,<sup>1, 2</sup> 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 (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.
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.
Multi-wavelength imaging polarimetry at far-infrared wavelengths has proven to be an excellent tool for studying
the physical properties of dust, molecular clouds, and magnetic fields in the interstellar medium. Although these
wavelengths are only observable from airborne or space-based platforms, no first-generation instrument for the
Stratospheric Observatory for Infrared Astronomy (SOFIA) is presently designed with polarimetric capabilities.
We study several options for upgrading the High-resolution Airborne Wideband Camera (HAWC) to a sensitive
FIR polarimeter. HAWC is a 12 × 32 pixel bolometer camera designed to cover the 53−215 μm spectral range
in 4 colors, all at diffraction-limited resolution (5−21 arcsec). Upgrade options include: (1) an external set of
optics which modulates the polarization state of the incoming radiation before entering the cryostat window;
(2) internal polarizing optics; and (3) a replacement of the current detector array with two state-of-the-art
superconducting bolometer arrays, an upgrade of the HAWC camera as well as polarimeter. We discuss a range
of science studies which will be possible with these upgrades including magnetic fields in star-forming regions
and galaxies and the wavelength-dependence of polarization.
SHARC-II is a 32 × 12 pixel submillimeter camera that is used with the ten-meter diameter Caltech Submillimeter
Observatory (CSO) on Mauna Kea. This camera can be operated at either 350 or 450 microns. We developed a module
that is installed at the CSO Nasmyth focus in order to convert SHARC-II into a sensitive imaging polarimeter, which we
refer to as "SHARP". SHARP splits the incident beam into two orthogonal polarized beams that are then re-imaged onto
different halves of the SHARC-II bolometer array. When this removable polarimetry module is in use, SHARC-II
becomes a dual-beam 12 × 12 pixel polarimeter. Sky noise is a significant source of error for submillimeter continuum
observations. Because SHARP will simultaneously observe two orthogonal polarization components, we are able to
eliminate or greatly reduce this source of error. Here we describe the design of SHARP and report preliminary results of
tests and observations carried out during our first two runs at CSO in August 2005 and January 2006.
The Submillimeter High Angular Resolution Camera II (SHARC-II) is a 32 x 12 pixel submillimeter camera that is used with the ten-meter diameter Caltech Submillimeter Observatory (CSO) on Mauna Kea. SHARC-II can be operated at either 350 or 450 microns. We are developing an optics module that we will install at a position between the SHARC-II camera and the focus of the CSO's secondary mirror. With our module installed, SHARC-II will be converted into a sensitive imaging polarimeter. The basic idea is that the module will split the incident beam coming from the secondary into two orthogonally polarized beams which are then re-imaged onto opposite ends of the “long and skinny” SHARC-II bolometer array. When this removable polarimetry module is in use, SHARC-II becomes a dual-polarization 12 x 12 pixel polarimeter. (The central 12 x 8 pixels of the SHARC-II array will remain unused.) Sky noise is a significant source of error for submillimeter continuum observations. Because our polarimetry module will allow simultaneous observation of two orthogonal polarization components, we will be able to eliminate or greatly reduce this source of error. Our optical design will include a rotating half-wave plate as well as a cold load to terminate the unused polarization components.
After the design of the calorimeter array for the high-resolution x-ray spectrometer (XRS) on the original Astro-E was frozen, new fabrication techniques became available and our understanding of these devices continually increased. We are now able to complete the optimization of this technology and, potentially, to increase the capability of new XRS instrument for Astro-E2, our on-going sounding recket experiments, and possible further applications. The most significant improvement comes from greatly reducing the excess noise of the ion-implanted thermistors by increasing the thickness of the implanted region.
A far-infrared polarimeter, Hale, will be proposed for the next round of instruments for SOFIA. Key features are: simultaneous detection of two components of polarization; detector arrays providing >4000 pixels on the sky; and four passbands between 53 μm and 215 μm, a range characterized by strong dependence of polarization on wavelength. At 53 μm the diffraction-limited resolution, 1.2 λ/D, will be 5.2 arcsec. In all passbands the systematic errors in polarization will be Δ(P) < 0.2%, Δθ< 2 °.
The University of Chicago polarimeter, Hertz, is designed for observations at the Caltech Submillimeter Observatory in the 350 micrometer atmospheric window. Initial observations with this instrument, the first array polarimeter for submillimeter observations, have produced over 700 measurements at 3(sigma) or better. This paper summarizes the characteristics of the instrument, presents examples of its performance including polarization maps of molecular clouds and regions near the Galactic center, and outlines the opportunities for improvements with emphasis on requirements for mapping widely extended sources.