The mid-infrared spectrometer and camera transit spectrometer (MISC-T) is one of the three baseline instruments for Origins Space Telescope (Origins) and provides the capability to assess the habitability of nearby exoplanets and search for signs of life. MISC-T employs a densified pupil optical design, and HgCdTe and Si:As detector arrays. This optical design allows the instrument to be relatively insensitive to minor line-of-sight pointing drifts and telescope aberrations, and the detectors do not require a sub-Kelvin refrigerator. MISC-T has three science spectral channels that share the same field-of-view by means of beam splitters, and all channels are operated simultaneously to cover the full spectral range from 2.8 to 20 μm at once with exquisite stability and precision (<5 ppm between 2.8 to 11 μm, <20 ppm between 11 and 20 μm). A Lyot-coronagraph-based tip–tilt sensor located in the instrument fore-optics uses the light reflected by a field stop, which corresponds to 0.3% of the light from the target, to send fine pointing information to the field steering mirror in the Origins telescope. An additional MISC Wide Field Imager (WFI) is studied as an upscope option for the Origins. MISC-WFI offers a wide field imaging (3 ′ × 3 ′ ) and low-resolution spectroscopic capability with filters and grating-prisms (grisms) covering 5 to 28 μm. The imaging capability of the MISC-WFI will be used for general science objectives. The low-resolution spectroscopic capability in MISC-WFI with a resolving power R ( = λ / Δλ) of a few hundreds will be used to measure the mid-infrared dust features and ionic lines at z up to ∼1 in the Origins mission’s Rise of Metals and Black Hole Feedback programs. The MISC-WFI also serves as a focal plane pointing and guiding instrument for the observatory, including when the MISC-T channel is performing its exoplanet spectroscopy observations.
We present an overview of the thermal and mechanical design of the Payload Module (PLM) of the next- generation infrared astronomy mission Space Infrared Telescope for Cosmology and Astrophysics (SPICA). The primary design goal of PLM is to cool the whole science assembly including a 2.5 m telescope and focal-plane instruments below 8 K. SPICA is thereby expected to have very low background conditions so that it can achieve unprecedented sensitivity in the mid- and far-infrared. PLM also provides the instruments with the 4.8 K and 1.8 K stages to cool their detectors. The SPICA cryogenic system combines passive, effective radiative cooling by multiple thermal shields and active cooling by a series of mechanical cryocoolers. The mechanical cryocoolers are required to provide 40 mW cooling power at 4.8 K and 10 mW at 1.8 K at End-of-Life (EoL). End-to-end performance of the SPICA cryocooler-chain from 300 K to 50 mK was demonstrated under the framework of the ESA CryoChain Core Technology Program (CC-CTP). In this paper, we focus on the recent progress of the thermal and mechanical design of SPICA PLM which is based on the SPICA mission proposal to ESA.
SMI (SPICA Mid-infrared Instrument) is one of the two focal-plane science instruments for SPICA. SMI is the Japanese led instrument proposed and managed by a nation-wide university consortium in Japan and planned to be developed in collaboration with Taiwan and the US. SMI covers the wavelength range from 12 to 36 μm with 4 separate channels: the low-resolution (R = 50-120) spectroscopy function for 17-36 μm, the broad-band (R = 5) imaging function at 34 μm, the mid-resolution (R = 1300-2300) spectroscopy function for 18-36 μm, and the high-resolution (R = 28000) spectroscopy function for 12-18 μm. In this paper, we show the results of our conceptual design and feasibility studies of SMI.
We present the new design of the cryogenic system of the next-generation infrared astronomy mission SPICA under the
new framework. The new design employs the V-groove design for radiators, making the best use of the Planck heritage.
The new design is based on the ESA-JAXA CDF study (NG-CryoIRTel, CDF-152(A)) with a 2 m telescope, and we
modified the CDF design to accommodate the 2.5 m telescope to meet the science requirements of SPICA. The basic
design concept of the SPICA cryogenic system is to cool the Science Instrument Assembly (SIA, which is the
combination of the telescope and focal-plane instruments) below 8K by the combination of the radiative cooling system
and mechanical cryocoolers without any cryogen.
KEYWORDS: Infrared telescopes, Space telescopes, Telescopes, Optical instrument design, Cryogenics, Infrared radiation, Cooling systems, Space telescopes, Cryogenics, Electrical breakdown, James Webb Space Telescope, Space operations
The Space Infrared Telescope for Cosmology and Astrophysics (SPICA) is a pre-project of JAXA in collaboration
with ESA to be launched in the 2020s. The SPICA mission is to be launched into a halo orbit around
the second Lagrangian point in the Sun-Earth system, which allows us to use effective radiant cooling in combination
with a mechanical cooling system in order to cool a 2.5m-class large IR telescope below 8K. Recently,
a new system design in particular thermal structure of the payload module has been studied by considering
the technical feasibility of a cryogenic cooled telescope within current constraints of the mission in the CDF
(Concurrent Design Facility) study of ESA/ESTEC. Then, the thermal design of the mechanical cooler system,
for which the Japanese side is responsible, has been examined based on the CDF study and the feasible
solution giving a proper margin has been obtained. As a baseline, 4K / 1K-class Joule-Thomson coolers are
used to cool the telescope and thermal interface for Focal Plane Instruments (FPIs). Additionally, two sets of
double stirling coolers (2STs) are used to cool the Telescope shield. In this design, nominal operation of FPIs
can be kept when one mechanical cooler is in failure.
SMI (SPICA Mid-infrared Instrument) is one of the two focal-plane scientific instruments planned for new SPICA, and
the Japanese instrument proposed and managed by a university consortium in Japan. SMI covers the wavelength range of
12 to 36 μm, using the following three spectroscopic channels with unprecedentedly high sensitivities: low-resolution
spectroscopy (LRS; R = 50 - 120, 17 - 36 μm), mid-resolution spectroscopy (MRS; R = 1300 - 2300, 18 - 36 μm), and
high-resolution spectroscopy (HRS; R = 28000, 12 - 18 μm). The key functions of these channels are high-speed dustband
mapping with LRS, high-sensitivity multi-purpose spectral mapping with MRS, and high-resolution molecular-gas
spectroscopy with HRS. This paper describes the technical concept and scientific capabilities of SMI.
Silicon carbide (SiC) has good thermal conductivity, high stiffness, and a relatively low specific density, all of which are advantageous to the application to telescopes operating at cryogenic temperatures. The first Japanese astronomical infrared space mission AKARI, which was launched in 2006 February and completed the second generation all-sky survey at 6 bands from mid- to far-infrared, employed a 700mm cryogenic telescope made of specially developed SiC. It was a sandwich-type of SiC composed of a lightweight porous core and a dense chemical vapor deposition (CVD) coat to decrease the specific density and facilitate machining for achieving the required surface figure accuracy. Measurements with an interferometer of 160-mm sample mirrors demonstrated that the AKARI mirror SiC had good thermal stability down to cryogenic temperatures (~6K), while the mirror support of the compact design became the primary source of the wave-front errors of the AKARI telescope. Taking the advantage of the heritage of the AKARI telescope development as well as ESA’s Herschel telescope, we are planning the next infrared space mission SPICA (Space Infrared Telescope for Cosmology and Astrophysics) of a 3.2m cooled telescope in participation of ESA using SiC-based materials. In this presentation, we summarize the development of AKARI SiC telescope and present the development activities of the SPICA telescope from the point of view of SiC being as the mirror material for cryogenic space infrared telescopes.
Mid-infrared Camera and Spectrometer (MCS) is one of focal plane instruments for SPICA (Space Infrared
Telescope for Cosmology and Astrophysics), which have 3 m class 6 K cooled telescope. MCS will provide wide
field imaging and low-, medium-, and high-resolution spectroscopic observing capabilities with 7 detectors in the
wavelength range from 5 to 38 micron. Large format array detectors are required in order to realize wide field of
view in imaging and wide spectral coverage in spectroscopy. We are planning to cover the wavelength range of
5-26 micron by Si:As IBC 2K x 2K and 20-38 micron by Si:Sb BIB 1K x 1K. The development status and their
design including the electrical and thermal design are described.
The Safari instrument on the Japanese SPICA mission is a zodiacal background limited imaging spectrometer offering a
photometric imaging (R ≈ 2), and a low (R = 100) and medium spectral resolution (R = 2000 at 100 μm) spectroscopy
mode in three photometric bands covering the 34-210 μm wavelength range. The instrument utilizes Nyquist sampled
filled arrays of very sensitive TES detectors providing a 2’x2’ instantaneous field of view. The all-reflective optical
system of Safari is highly modular and consists of an input optics module containing the entrance shutter, a calibration
source and a pair of filter wheels, followed by an interferometer and finally the camera bay optics accommodating the
focal-plane arrays. The optical design is largely driven and constrained by volume inviting for a compact three-dimensional
arrangement of the interferometer and camera bay optics without compromising the optical performance
requirements associated with a diffraction- and background-limited spectroscopic imaging instrument. Central to the
optics we present a flexible and compact non-polarizing Mach-Zehnder interferometer layout, with dual input and output
ports, employing a novel FTS scan mechanism based on magnetic bearings and a linear motor. In this paper we discuss
the conceptual design of the focal-plane optics and describe how we implement the optical instrument functions, define
the photometric bands, deal with straylight control, diffraction and thermal emission in the long-wavelength limit and
interface to the large-format FPA arrays at one end and the SPICA telescope assembly at the other end.
We present the current status of the development of the SPICA Coronagraph Instrument (SCI). SPICA is a next-generation
3-meter class infrared telescope, which will be launched in 2022. SCI is high-contrast imaging, spectroscopic
instrument mainly for direct detection and spectroscopy of extra-solar planets in the near-to-mid infrared wavelengths to
characterize their atmospheres, physical parameters and evolutionary scenarios. SCI is now under the international
review process. In this paper, we present a science case of SCI. The main targets of SCI, not only for direct imaging but
also for spectroscopy, are young to matured giant planets. We will also show that some of known exoplanets by ground-based
direct detection are good targets for SCI, and a number of direct detection planets that are suitable for SCI will be
significantly increased in the next decade. Second, a general design of SCI and a key technology including a new high-throughput
binary mask coronagraph, will be presented. Furthermore, we will show that SCI is potentially capable of
achieving 10-6 contrast by a PSF subtraction method, even with a telescope pointing error. This contrast enhancement
will be important to characterize low-mass and cool planets.
SPICA (Space Infrared Telescope for Cosmology and Astrophysics) is a Japan-led infrared astronomical satellite project
with a 3.2-m lightweight cryogenic telescope. The SPICA telescope has stringent requirements such as that for the
imaging performance to be diffraction-limited at the shortest core wavelength of 5 microns at the operating temperature
of 6 K. The design of the telescope system has been studied by the Europe-Japan telescope working group led by ESA
with the European industries, the results of which will be presented in other papers. We here present our recent optical
testing activities in Japan for the SPICA telescope, focusing on the experimental and numerical studies of stitching
interferometry. The full pupil of the SPICA telescope will be covered by a sub-pupil array consisting of small
autocollimating flat mirrors (ACFs), which are rotated with respect to the optical axis of the telescope. For preliminary
stitching experiments, we have fabricated an 800-mm lightweight telescope all made of the C/SiC called HBCesic, which
is a candidate mirror material for the SPICA telescope, and started optical testing with 900-mm and 300-mm ACFs at an
ambient temperature. ACFs can suffer significant surface deformation in testing a telescope at cryogenic temperatures,
which is difficult to be measured directly. We therefore investigate the effects of the surface figure errors of the ACFs on
stitching results by numerical simulation.
The Space Infrared Telescope for Cosmology and Astrophysics (SPICA) is a 3.2m cooled (below 6K) telescope
mission which covers mid- and far-IR waveband with unprecedented sensitivity. An overview of recent design
updates of the Scientific Instrument Assembly (SIA), composed of the telescope assembly and the instrument
optical bench equipped with Focal Plane Instruments (FPIs) are presented. The FPI international science and
engineering review is on-going to determine the FPI suite onboard SPICA: at present the mandatory instruments
and functions to perform the unique science objectives of the SPICA mission are now consolidated. The final
decision on the composition of the FPI suite is expected in early 2013. Through the activities in the current pre-project
phase, several key technical issues which impact directly on the instruments’ performances and the science
requirements and the observing efficiency have been identified, and extensive works are underway both at
instrument and spacecraft level to resolve these issues and to enable the confirmation of the SPICA FPI suite.
We present the current status of the development of a far-infrared monolithic Ge:Ga photoconductor array
proposed for the SAFARI instrument onboard SPICA, which is a future infrared space mission. SPICA has a
large (3-m class) cooled (<6 K) telescope, which enables us to make astronomical observations with high spatial
resolution and unprecedented sensitivity in the mid- and far-infrared wavelength. As a candidate detector to
cover the 45-110 μm band of a far-infrared focal plan instrument of SAFARI, we are developing a large format
monolithic Ge:Ga array. The monolithic Ge:Ga array is directly connected to cryogenic readout electronics
(CRE) using the Au-Indium bumping technology. Our goal is to develop a 64×64 Ge:Ga array, on the basis
of existing technologies and experience in making the 3×20 Ge:Ga monolithic arrays for the AKARI satellite.
In order to realize a larger format array with better sensitivity than that of the AKARI array, we have been
making some technical improvements; (1) development of the Au-In bumping technology to realize the large
format array, (2) optimization of the structure of the transparent electrode to achieve the better sensitivity, (3)
development of an anti-reflection coating to reduce interference fringe between the Ge substrate, and (4) Use
of the low-noise cryogenic readout electronics with low power consumption. We fabricated the prototype 5×5
Ge:Ga arrays to demonstrate and evaluate the properties of monolithic array. We demonstrate experimentally
the feasibility of these elemental technologies, and also show the results of performance measurements for the
prototype Ge:Ga arrays.
There are two different types of beam combination: Fizeau interferometer and Michelson interferometer.
Pupil plane beam combination is referred as Fizeau interferometer. On the other hand, image plane beam
combination is referred as Michelson interferometer. In general, working principles of Michelson
interferometers are based on double Fourier interferometry. It is possible to acquire two-dimensional
spatial and one-dimensional spectral information of the sky by applying a Fourier transform spectrometer
algorithm and the Van Cittert-Zernike theorem. This imaging scheme is referred to as the double Fourier
interferometry. On the other hand, it is so far thought to be difficult to perform the imaging with a Fizeau
interferometer, because Fizeau interferometers basically don't have a delay line that is equipped with
Michelson interferometers. Here, Matsuo et al.1 presented a new spectral imaging method for Fizeau
interferometers, based on double Fourier interferometry. They noticed that a delay axis in Michelson
interferometers is equal to the axis of a fringe pattern on an image plane in Fizeau interferometers.
Therefore, this new approach can acquire three-dimensional information of the sky using a linear array
detector placed on the image plane. In this paper, we compare the new spectral imaging method for
Fizeau interferometer with the conventional one used for Michelson interferometer and discuss spectral
resolutions and field of views of these imaging methods.
We have developed a sensor optical system for the Far Infrared Interferometric Telescope (FITE). The spatial
resolution of FITE is expected to be 2.5 arcseconds. In order to derive the spatial extent of target objects, the
visibility of interference fringes has to be measured precisely. For this purpose, we constructed the focal plane
assembly of the FITE interferometer with the sensor optics. The focal plane is the entrance focus of the sensor
optics. A far-infrared (FIR) array detector is installed on the final focal plane of the sensor optics. Its camera
optics has F/106 beam for each beam of the interferometer. The PSF is dominated by diffraction, and its size
corresponds approximately to the array size so that the fringe pattern can be measured by the array in real time.
This system employs of two IR detectors and an optical CCD. The FIR detector has a format of 1.5mm ×15
pixels. In addition to the FIR array detector, we have a mid-IR detector and an optical CCD. They are also
installed on the final focal plane of the sensor optics. These two detectors are used for the precise alignment of the
interferometer optics.
We present the in-orbit performance of slow-scan observation of the Far-Infrared Surveyor (FIS) onboard the
AKARI satellite. The FIS, one of the two focal-plane instruments of AKARI, has four photometric bands from
50-180 μm with two kinds of Ge:Ga array detectors. In addition to the All-Sky Survey, the FIS also took images
of specific targets by the slow-scan. Because of the longer exposure time on a targeted source, the sensitivity
in the slow-scan mode is 1-2 orders of magnitude better than that in the All-Sky Survey mode. In order to
evaluate the point spread functions (PSFs), several bright point-like objects such as asteroids, stars, and galaxies
were observed. Though significant enhancements are seen at the tails of the PSFs, the derived full width at
the half maximum (FWHM) are consistent with those expected from the optical simulation and the laboratory
measurements; ~40" for two shorter wavelength bands and ~60" for two longer wavelength bands, respectively.
The absolute photometric calibration has been performed by observing well established photometric calibration
standards (asteroids and stars) in a wide range of fluxes. After the establishment for the method of the aperture
photometry, the photometric accuracy for point sources is less than 10% in all bands.
We report the in-orbit performance of the AKARI/Far-Infrared Surveyor Ge:Ga photoconductors, focusing on the
transient response and the radiation effects, to perform the characterization of these effects for data analyses. The
behavior for these effects is found to be significantly different between the Short-Wavelength and Long-Wavelength
array detectors of the FIS, most probably due to the difference in the array configuration. We discuss cosmic-ray
radiation effects, referring to the results of pre-flight proton-beam irradiation measurements. We also describe our efforts
to correct the slow transient response of the detectors by adopting a physical approach.
We have developed an imaging Fourier transform spectrometer (iFTS) for space-based far-infrared astronomical
observations. The iFTS employs newly developed photoconductive detector arrays with a capacitive transimpedance
amplifier, which makes the iFTS a completely unique instrument. The iFTS was installed as a
function of the far-infrared instrument (FIS: Far-Infrared Surveyor) on the Japanese astronomical satellite,
AKARI, which was launched on February 21, 2006 (UT) from the Uchinoura Space Center. The iFTS had
worked properly in the space environment as well as in laboratory for more than one year before liquid helium
ran out on August 26, 2007. The iFTS was operated nearly six hundreds of pointed observations. More than
one hundred hours of astronomical observations and almost the same amount of time for calibrations have been
carried out in the mission life. Meanwhile, it becomes clear that the detector transient effect is a considerable
factor for FTSs with photoconductive detectors. In this paper, the instrumentation of the iFTS and interesting
phenomena related to FTSs using photoconductive detectors are described, and the calibration strategy of the
iFTS is discussed briefly.
We present our high spectral resolution tandem Fabry-Perot (FP) spectrometer for detecting the pure rotational
transition line of molecular Hydrogen S (1) at 17.035 μm. It is designed to be attached to a new dedicated 1
m telescope planned to be put at a dry and high-altitude site. The spectrometer has two sequentially placed
FP units (order 1000 and 99 with finesse >50) consisting of ZnSe etalons and one narrow band filter. We will
be able to obtain high spectral resolution of R=50,000 at 17.035 μm. The ZnSe etalons of 110mm diameter
with >94% reflectance are to be provided from Barr Associates. The interval and tilt of etalons are sensed and
regulated by piezo actuators and newly-developed capacitance sensors, which resolve 100nm in vacuum and 30K
environment. By changing the interval, we change the wavelength of transmission up to 17.2 μm, corresponding
toν = 3000 km/s. We adopt an on-axis catadioptric system, in which the two FP units are placed. The focal
plane detector is a Raytheon SB-774, 320×240 pixel array of Si:As, yielding 9.1 × 6.8 arcmin2 field of view with
1.7 arcsec pixel scale. To suppress the thermal background radiation and dark current of the Si:As detector, the
system is cooled down to 6K at the detector and 35K for the whole optical system by two refrigerators. The
development of spectrometer will be completed in 2007.
We present pre-flight performance of a monolithic Ge:Ga array detector for Far-Infrared Surveyor (FIS) onboard the ASTRO-F satellite. The primary purpose of the ASTRO-F mission is to perform an all-sky survey in four photometric bands form 50-200 um. For shorter half of this spectral range, 50-110 um, we have developed the monolithic Ge:Ga array which is directly connected to a cryogenic readout electronics (CRE) with the indium-bump technology. In order to investigate the point-source detectability in the survey observation, we carry out a simulation experiment. The experiment was done by taking a image of moving pinholes located on the focal plane of the FIS optics. A clear image without any distortion was obtained, but the size of point source image is slightly larger than expected. We estimate the detection limit in the survey observation by taking account of all detector properties including the imaging performance. The results show that the detector sensitivity is sufficiently high to meet the requirement of the ASTRO-F mission.
The Far-Infrared Surveyor (FIS) is a focal plane instrument of the ASTRO-F satellite, and is designed primarily to achieve far-infrared all sky survey with four photometric bands in wavelength range of 50 - 200um. Compared to IRAS, the FIS has higher sensitivity, higher spatial resolution, and longer wavelength coverage. The FIS also has spectroscopic capability with a Fourier transform spectrometer (FTS). In order to assemble these two kinds of instrument into a small and light body, we have developed new compact detector arrays and adopt the unique optical design. In the first half year of the ASTRO-F mission, the all sky survey is performed intensively, and is completed in the following half year. In addition to this survey, the telescope can be kept to a specific direction during 10 minutes for pointing observations. In pointing observations, we can take deep photometric images by using the photometric mode, or can take spectra by using the FTS. According to the laboratory calibration, it is expected that the detection limit of the all sky survey is almost one order of magnitude better than the IRAS one. The FTS could take spectra with full spectral resolution for about two orders of magnitude brighter sources than the detection limit of the all sky survey for one pointing observation. Due to the imaging FTS, the observing efficiency is much improved for the extended sources. The FIS will provide us unique and valuable observational data in the far-infrared wavelength region.
We have developed the imaging Fourier Transform Spectrometer (FTS) for the FIS (Far-Infrared Surveyor) onboard the ASTRO-F satellite. A Martin-Puplett interferometer is adopted to achieve high optical efficiency in a wide wavelength range. The total optical efficiency of this spectrometer is achieved 40-80% of the ideal value which is 25% of the incident flux. The wavelength range of 50-200μm is covered with two kinds of detector; the monolithic Ge:Ga photoconductor array for short wavelength (50-110μm) and the stressed Ge:Ga photoconductor array for long wavelength (110-200μm). The spectral resolution expected from the maximum optical path difference is 0.18cm-1.
In order to evaluate the spectral resolution of the FTS, we measured absorption lines of H2O in atmosphere using the optics of the FTS with a bolometer at the room temperature. The measured line widths are consistent with the expected instrumental resolution of 0.18 cm-1. Some spectral measurements at the cryogenic temperature were carried out by using cold blackbody sources whose temperatures are controlled in a range from 20 to 50 K. The derived spectra considering with the spectral response of the system are consistent with expected ones.
Spectroscopic observations with the FTS will provide a lot of astronomical information; SED of galaxies detected in the all sky survey and the physical diagnostics of the interstellar matter by using the excited atomic or molecular lines.
Far-Infrared Surveyor (FIS) is one of the two focal plane instruments of ASTRO-F which is a Japanese infrared astronomical satellite and is planned to launch in 2004. The FIS has spectroscopic capability by a Fourier transform spectrometer (FTS) covering 50-200cm-1 with spectral resolution of 0.2-0.33 cm-1 in addition to the primary purpose of FIS (an all-sky photometric survey). The Martin-Puplett interferometer is adopted as the method for spectroscopy in order to achieve high optical efficiency in a wide wavelength range.
The most important issue of the FTS is the development of driving mechanism in order to scan a moving mirror with high optical performances. By the present we succeed to develop the driving mechanism satisfying a lot of limitations and requirements as a instrument onboard satellite. Furthermore the wire-grid polarizers are evaluated in optical performance, these are usable for polarized interferomter. We also measure FIR spectrum using Spectroscopy mode of FIS, and many absorption lines of H2O are detected on continuum spectrum of atmosphere. And the interferogram and spectrum are derived at low temperature (2K) that is practically used in space. The spectrum resembles expected one which are considered with optical components for flight model. The detection limit are estimated combining performances of optical components and detectors, the FISP has sufficient performance to archive objective sciences. FTS will provide a lot of astronomical information; determination of the SED in high-z objects detected by the survey observation of ASTRO-F, the redshift of such objects, and the physical conditions that are hard to be derived by optical/NIR-MIR observations, from FIR lines.
ASTRO-F is a Japanese infrared satellite, which is scheduled for launch in early 2004. Far-infrared instrument that will be onboard ASTRO-F, Far-Infrared Surveyor (FIS), will perform the four-color all sky survey in the 50-200 um wavelength range with the diffraction-limited spatial resolution for 67-cm diameter telescope. For short-wave photometric bands of 50-110 um, we have developed a monolithic Ge:Ga two-dimensional array detector with no light cavity. This top-illumination type array design is promising for making future large-format array. The monolithic Ge:Ga is directly attached onto cryogenic readout electronics, capacitive trans-impedance amplifier composed of silicon p-MOSFETs, designed specially for low-temperature use. Results of the detector measurements show that the device works properly and sensitive enough for astronomical applications. Complex behavior of the detector, such as non-linearity of the integration ramp, transient response, non-uniform responsivity in the array, and cross-talk response, which may cause systematic error in the photometry, have been found. But, these effects are ~10% of major part of the signal and correctable with accuracy of a few %.
The Japanese infrared astronomical satellite, ASTRO-F, employs the Far-Infrared Surveyor (FIS) for all sky survey. The FIS has two detector arrays; one covers from 50 to 110 μm wavelength, the other covers from 110 to 200 μm. Each of them uses Ge:Ga operating at 2K. We have developed and evaluated the preamplifiers for these detector arrays. The preamplifiers are required to work at 2K with low noise and low power dissipation. In this paper, we report on the development and evaluation of these cryogenic preamplifiers.
The ASTRO-F project is currently in its final stage of proto-model, which is constructed same as flight-model. Since instrument goals of the Far-Infrared Surveyor (FIS) are unprecedented achievement of high sensitivity and high spatial resolution in far-infrared wavelength, the proto- model stage is important to prove the performance as the flight instrument. We mainly present here the latest optical, thermal, and mechanical properties of the proto- model of the FIS.
We have developed the new balloon-borne telescope, Far Infrared Balloon-Borne Experiment (FIRBE), to survey the far-infrared radiations of star-forming regions. The primary mirror is an offset parabolid with a diameter of 50 cm (F/2) and telescope structure is made from Carbon Fiber Reinforced Plastics to lighten the whole telescope and hold the strain of image at the focal position minimum since its thermal contraction is very small. The telescope optics is off-axis system with on second mirror and no warm support structure in its optical path in order to reduce the infrared emission from the telescope structure itself.
We present a conceptual design of a future Japanese IR astronomical satellite: the HIII/L2 mission. We propose a 'warm launch' cooled telescope; the telescope is to be launched at ambient temperature and is to be cooled in orbit to 4.5K by a modest cryogenic cooler with the help of radiative cooling. Since liquid helium and hence a heavy vacuum vessel are not longer required, the warm launch design reduces the weight of the satellite dramatically. We propose to launch this satellite into a halo orbit around S- E L2, one of the Sun-Earth Lagrangian liberation points. The S-E L2 is an ideal orbit for IR astronomy, since (1) radiative cooling can become very effective, and (2) by the Japanese H-IIA launching vehicle. This mission focuses on high-resolution mid- to far-IR observations with unprecedented sensitivity, since the large aperture reduces confusion noise and the cooled optics suppresses instrumental background radiation. The HII/L2 mission is an ideal observatory-type platform to make follow-up observations to the ASTRO-F/IRIS survey mission. The target launch year is 2010.
Ge:Ga far-IR photoconductor 2D direct hybrid arrays are being developed for application in the focal-plane detectors of the far-IR surveyor, one of the two main instruments of the IR imaging surveyor satellite. The arrays are composed of Ge:Ga photoconductor arrays fabricated on one chip, Si- pMOS readout integrated circuits, and a hybridization of them done by using indium bump technology.
The far-IR Surveyor (IRS) is one of the two focal plane instruments of the IR Imaging Surveyor, IRIS, which is a Japanese IR astronomical satellite. FIS is designed primarily to perform an all-sky survey with several photometric bands like IRAS. Advantages of FIS to IRAS are its high detectivity of point sources and its longer wavelength capability. These features are gained by remarkable improvement in detector technology. FIS adopts currently developed unstressed and stressed Ge:Ga array detectors to cover 50 to 200 micrometers in wavelength. Due to highly sensitive detector system, it is expected to detect over 10 million objects by the all-sky, including a lot of high-z objects. FIS also has spectroscopic capability by a Fourier spectrometer covering 50 to 200 cm-1 in wave number with spectral resolution of 0.5 cm-1. The same detector arrays of the scanner are used and these two functions are switched. As a result of combining a spectroscopic function with the scanner, FIS becomes a unique instrument. The basic observation mode of the FIS is an all-sky survey using the scanner. The spectroscopic function is operated in the pointing mode in which it can take longer integration time. Spectral information can be used to estimate the redshifts of strange objects detected by the all-sky survey. The spectrometer is also a powerful instrument to reveal the physical properties of galactic and nearby sources.
Low-noise and low-power cryogenic readout electronics are developed for a focal plane instrument of the IR Imaging Surveyor. We measured the static characteristics and the noise spectra of several types of silicon MOSFETs at the cryogenic temperature where silicon JFETs do not work well due to the carrier freeze-out. The 'kink' behavior of n- channel MOSFETs was observed below the carrier freeze-out temperature, but it was not obvious for the p-channel MOSFET. It was demonstrated the p-channel MOSFETs can be used for the cryogenic readout electronics of the IRIS's far-IR array with an acceptable performance. The amplifier integrated with these MOSFETs showed low-noise at 2K under a low power consumption of 1 (mu) W per MOSFET. We now design and evaluate several circuits that are fabricated by the CMOS process for cryogenic readout.
We describe the design and performance of the near IR telescope experiment (NITE), a rocket-borne instrument designed to search for IR emission from baryonic dark matter in the halos of nearby edge-on spiral galaxies. A 256 X 256 InSb array at the focus of a 16.5 cm liquid-helium- cooled telescope achieves near-background-limited sensitivity in a 3.5-5.5 micrometers waveband where the local foreground from zodiacal emission is at a minimum. This experiment represents the first scientific application of a low-background IR InSb array, a precursor to the InSb arrays intended for SIRTF, in a space-borne observation. We describe the flight performance of the instrument and preliminary scientific result from an observation of NGC 4565.
We are developing a stressed Ge:Ga 2D array detector that will be used for balloon-borne and satellite-born astronomical observations at wavelength between 100 and 200 micrometers . We have succeeded in making a 4 X 8 element stressed array detector with a stress of 600 N/mm2 and responsivity peak wavelength moved to about 165 micrometers . This has the largest number of pixels at the present time. The responsivities of the detector are high enough as well as those currently in use. This detector has a compact structure and a small total pixel size, and thus, it can be used for satellite-born instruments that have severe space limitation.
KEYWORDS: Near infrared spectroscopy, Stars, Spectroscopy, Calibration, Camera shutters, Space telescopes, Sensors, Solids, Space operations, Surface conduction electron emitter displays
The near-infrared spectrometer (NIRS) is one of the focal plane instruments of the infrared telescope in space (IRTS). The NIRS is a simple grating spectrometer with two element InSb linear arrays, and was designed to measure the absolute sky brightness at the wavelengths from 1.4 to 4.0 micrometer with a spectral resolution of 0.13 micrometer and a beam size of 8 feet by 8 feet. The IRTS was launched on 1995 March 18. The NIRS worked well throughout the observation period from March 29 to April 25, and scanned about 7% of the entire sky. Multiple passage of bright stars through the NIRS field of view enabled us to reconstruct the beam pattern and to calibrate the sensitivity. Those flight data confirmed good performance of the NIRS on the orbit as was expected from the preflight measurements.
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