The mid/far infrared hosts a wealth of spectral information that allows direct determination of the physical state of matter in a large variety of astronomical objects, unhindered by foreground obscuration. Accessing this domain is essential for astronomers to much better grasp the fundamental physical processes underlying the evolution of many types of celestial objects, ranging from protoplanetary systems in our own milky way to 10-12 billion year old galaxies at the high noon of galaxy formation in our universe. The joint ESA/JAXA SPICA mission will give such access for the astronomical community at large, by providing an observatory with unprecedented mid- to far-infrared imaging, polarimetric and spectroscopic capabilities.
Measurements in the infrared wavelength domain allow us to assess directly the physical state and energy balance of cool matter in space, thus enabling the detailed study of the various processes that govern the formation and early evolution of stars and planetary systems in the Milky Way and of galaxies over cosmic time. Previous infrared missions, from IRAS to Herschel, have revealed a great deal about the obscured Universe, but sensitivity has been limited because up to now it has not been possible to fly a telescope that is both large and cold. Such a facility is essential to address key astrophysical questions, especially concerning galaxy evolution and the development of planetary systems.
SPICA is a mission concept aimed at taking the next step in mid- and far-infrared observational capability by combining a large and cold telescope with instruments employing state-of-the-art ultra-sensitive detectors. The mission concept foresees a 2.5-meter diameter telescope cooled to below 8 K. Rather than using liquid cryogen, a combination of passive cooling and mechanical coolers will be used to cool both the telescope and the instruments. With cooling not dependent on a limited cryogen supply, the mission lifetime can extend significantly beyond the required three years. The combination of low telescope background and instruments with state-of-the-art detectors means that SPICA can provide a huge advance on the capabilities of previous missions.
The SPICA instrument complement offers spectral resolving power ranging from ~50 through 11000 in the 17-230 µm domain as well as ~28.000 spectroscopy between 12 and 18 µm. Additionally, SPICA will be capable of efficient 30-37 µm broad band mapping, and small field spectroscopic and polarimetric imaging in the 100-350 µm range. SPICA will enable far infrared spectroscopy with an unprecedented sensitivity of ~5x10-20 W/m2 (5σ/1hr) - at least two orders of magnitude improvement over what has been attained to date. With this exceptional leap in performance, new domains in infrared astronomy will become accessible, allowing us, for example, to unravel definitively galaxy evolution and metal production over cosmic time, to study dust formation and evolution from very early epochs onwards, and to trace the formation history of planetary systems.
The Japanese SPace Infrared telescope for Cosmology and Astrophysics, SPICA, aims to provide astronomers with a truly new window on the universe. With a large -3 meter class- cold -6K- telescope, the mission provides a unique low background environment optimally suited for highly sensitive instruments limited only by the cosmic background itself. SAFARI, the SpicA FAR infrared Instrument SAFARI, is a Fourier Transform imaging spectrometer designed to fully exploit this extremely low far infrared background environment. The SAFARI consortium, comprised of European and Canadian institutes, has established an instrument reference design based on a Mach-Zehnder interferometer stage with outputs directed to three extremely sensitive Transition Edge Sensor arrays covering the 35 to 210 μm domain. The baseline instrument provides R > 1000 spectroscopic imaging capabilities over a 2’ by 2’ field of view. A number of modifications to the instrument to extend its capabilities are under investigation. With the reference design SAFARI’s sensitivity for many objects is limited not only by the detector NEP but also by the level of broad band background radiation – the zodiacal light for the shorter wavelengths and satellite baffle structures for the longer wavelengths. Options to reduce this background are dedicated masks or dispersive elements which can be inserted in the optics as required. The resulting increase in sensitivity can directly enhance the prime science goals of SAFARI; with the expected enhanced sensitivity astronomers would be in a better position to study thousands of galaxies out to redshift 3 and even many hundreds out to redshifts of 5 or 6. Possibilities to increase the wavelength resolution, at least for the shorter wavelength bands, are investigated as this would significantly enhance SAFARI’s capabilities to study star and planet formation in our own galaxy.
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.
The Japanese SPace Infrared telescope for Cosmology and Astrophysics, SPICA, will provide astronomers with a long
awaited new window on the universe. Having a large cold telescope cooled to only 6K above absolute zero, SPICA will
provide a unique environment where instruments are limited only by the cosmic background itself. A consortium of
European and Canadian institutes has been established to design and implement the SpicA FAR infrared Instrument
SAFARI, an imaging spectrometer designed to fully exploit this extremely low far infrared background environment
provided by the SPICA observatory.
SAFARI’s large instantaneous field of view combined with the extremely sensitive Transition Edge Sensing detectors
will allow astronomers to very efficiently map large areas of the sky in the far infrared – in a square degree survey of a
1000 hours many thousands of faint sources will be detected, and a very large fraction of these sources will be fully
spectroscopically characterised by the instrument. Efficiently obtaining such a large number of complete spectra is
essential to address several fundamental questions in current astrophysics: how do galaxies form and evolve over cosmic
time?, what is the true nature of our own Milky Way?, and why and where do planets like those in our own solar system
come into being?
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.
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 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 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 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.
Gallium-doped germanium (Ge:Ga) extrinsic photoconductor is one of a excellent quantum detector in the terahertz range. Design of a novel wave-guide Ge:Ga photoconductor integrated with silicon solid immersion lens and fabrication technology for linear arrays is presented. The possibilities to extend this technology for realizing large format Ge:Ga waveguide 2D-array detector are discussed.
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 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 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.
The far-infrared line mapper (FILM) is a far-infrared spectrometer and in one of four focal plane instruments of the infrared telescope in space (IRTS), FILM was designed for wide area intensity mapping of far-infrared emission from interstellar gas and dust in the galaxy. The targets are the [CII] 158 micrometer line of the ionized carbon, the [OI] 63 micrometer line of the oxygen atom, and the continuum emission at 155 and 160 micrometer from the interstellar dust grain. A cylindrically concave varied line-space grating and a linear array of stressed Ge:Ga were successfully developed and allowed us to make a compact spectrometer compatible to severe limitations of the small cryogenic telescope. The IRTS, onboard the space flyer unit (SFU), was launched by a HII rocket on March 18, 1995 and was recovered by a STS on January 13, 1996. The FILM worked very well during four weeks allocated for the IRTS observation and produced a lot of valuable data. The sensitivity and the spatial resolution for the [CII] line are an order of magnitude better than the previous work.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.