Fluctuations in the extragalactic background light trace emission from the history of galaxy formation, including the emission from the earliest sources from the epoch of reionization. A number of recent near-infrared measure- ments show excess spatial power at large angular scales inconsistent with models of z < 5 emission from galaxies. These measurements have been interpreted as arising from either redshifted stellar and quasar emission from the epoch of reionization, or the combined intra-halo light from stars thrown out of galaxies during merging activity at lower redshifts. Though astrophysically distinct, both interpretations arise from faint, low surface brightness source populations that are difficult to detect except by statistical approaches using careful observations with suitable instruments. The key to determining the source of these background anisotropies will be wide-field imaging measurements spanning multiple bands from the optical to the near-infrared. The Cosmic Infrared Background ExpeRiment 2 (CIBER-2) will measure spatial anisotropies in the extra- galactic infrared background caused by cosmological structure using six broad spectral bands. The experiment uses three 2048 x 2048 Hawaii-2RG near-infrared arrays in three cameras coupled to a single 28.5 cm telescope housed in a reusable sounding rocket-borne payload. A small portion of each array will also be combined with a linear-variable filter to make absolute measurements of the spectrum of the extragalactic background with high spatial resolution for deep subtraction of Galactic starlight. The large field of view and multiple spectral bands make CIBER-2 unique in its sensitivity to fluctuations predicted by models of lower limits on the luminosity of the first stars and galaxies and in its ability to distinguish between primordial and foreground anisotropies. In this paper the scientific motivation for CIBER-2 and details of its first flight instrumentation will be discussed, including detailed designs of the mechanical, cryogenic, and electrical systems. Plans for the future will also be presented.
We are now investigating and studying a small satellite mission HiZ-GUNDAM for future observation of gamma-ray bursts (GRBs). The mission concept is to probe “the end of dark ages and the dawn of formation of astronomical objects”, i.e. the physical condition of early universe beyond the redshift z > 7. We will consider two kinds of mission payloads, (1) wide field X-ray imaging detectors for GRB discovery, and (2) a near infrared telescope with 30 cm in diameter to select the high-z GRB candidates effectively. In this paper, we explain some requirements to promote the GRB cosmology based on the past observations, and also introduce the mission concept of HiZ-GUNDAM and basic development of X-ray imaging detectors.
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.
Ultraviolet emission from the first generation of stars in the Universe ionized the intergalactic medium in a
process which was completed by z ~ 6; the wavelength of these photons has been redshifted by (1 + z) into
the near infrared today and can be measured using instruments situated above the Earth's atmosphere. First
flying in February 2009, the Cosmic Infrared Background ExpeRiment (CIBER) comprises four instruments
housed in a single reusable sounding rocket borne payload. CIBER will measure spatial anisotropies in the
extragalactic IR background caused by cosmological structure from the epoch of reionization using two broadband
imaging instruments, make a detailed characterization of the spectral shape of the IR background using a
low resolution spectrometer, and measure the absolute brightness of the Zodiacal light foreground with a high
resolution spectrometer in each of our six science fields. The scientific motivation for CIBER and details of its
first and second flight instrumentation will be discussed. First flight results on the color of the zodiacal light
around 1 μm and plans for the future will also be presented.
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 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 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.
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 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.
Design and characterization of optical-THz phase-matched traveling-wave photomixers for difference-frequency generation of THz waves are presented. A dc-biased coplanar stripline fabricated on low-temperature-grown GaAs is illuminated by two non-collinear laser beams which generate moving interference fringes that are accompanied by THz waves. By tuning the offset angle between the two laser beams, the velocity of the interference fringe can be matched to the phase velocity of the THz wave in the coplanar stripline. The generated THz waves are radiated into free space by the antenna at the termination of the stripline. Enhancement of the output power was clearly observed when the phase-matching condition was satisfied. The output power spectrum has a 3-dB bandwidth of 2 THz and rolls off as approximately 9 dB/Oct which is determined by the frequency dependent attenuation in the stripline, while the bandwidth of conventional photomixer design has the limitation by the RC time constant due to the electrode capacitance. The device can handle the laser power of over 380 mW, which is 5 times higher than the maximum power handring capability of conventional small area devices. The results show that the traveling-wave photomixers have the potential to surpass small area designs, especially at higher frequencies over 1 THz, owing to their great thermal dissipation capability and capacitance-free wide bandwidth.
We developed a tunable, cavity-locked diode laser source at 850 nm for difference-frequency generation of coherent THz- waves. The difference frequency is synthesized by three fiber-coupled external-cavity diode lasers, where tow of the lasers are locked to adjacent modes of an ultra-stable Fabry-Perot cavity and the third laser is offset-phase- locked to the second cavity-locked laser using a tunable microwave oscillator. The first cavity-locked laser and the offset-locked laser produces the difference frequency, whose value is precisely determined by sum of integer multiple of free spectral range of the Fabry-Perot cavity and the offset frequency. The difference-frequency signal is amplified to 500 mW by the master oscillator power amplifier technique, simultaneous two-frequency injection-seeding with a single semiconductor optical amplifier. Here we demonstrate the difference-frequency generation of THz waves with the low- temperature-grown GaAs photomixers and its application to high-resolution spectroscopy of simple molecules. An absolute frequency calibration was carried out with an accuracy of approximately 10-7 using CO lines in the THz region.
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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