The Mid-Infrared Multi-field Imager for gaZing at the UnKnown Universe (MIMIZUKU) is a mid-infrared camera and spectrograph developed as a first-generation instrument on the University of Tokyo Atacama Observatory (TAO) 6.5-m telescope. MIMIZUKU covers a wide wavelength range from 2 to 38 μm and has a unique optical device called Field Stacker which realizes accurate calibration of variable atmospheric transmittance with a few percent accuracy. By utilizing these capabilities, MIMIZUKU realizes mid-infrared long-term monitoring, which has not been challenged well. MIMIZUKU has three optical channels, called NIR, MIR-S, and MIR-L, to realize the wide wavelength coverage. The MIR-S channel, which covers 6.8–26 μm, has been completed by now. We are planning to perform engineering observations with this channel at the Subaru telescope before the completion of the TAO 6.5-m telescope. In this paper, we report the results of the laboratory tests to evaluate the optical and detector performances of the MIR-S channel. As a result, we confirmed a pixel scale of 0.12 arcsec/pix and a vignetting- free field of view of 2./0 1./8. The instrument throughputs for imaging modes are measured to be 20–30%. Those for N - and Q -band spectroscopy modes are 17 and 5%, respectively. As for the detector performance, we derived the quantum efficiency to be 40–50% in the mid-infrared wavelength region and measured the readout noise to be 3000–6000 electrons, which are larger than the spec value. It was found that this large readout noise degrades the sensitivity of MIMIZUKU by a factor of two.
We introduce a new method named as “weighted average method" to reduce atmospheric noise on the images in ground based mid-infrared observations. The main idea of this method is to find a sky frame corresponded to an object frame by superposition of several sky frames, instead of the conventional chop-and-nod observation technique. This is very useful not only for improving the observing efficiency but also for taking images of extended objects larger than the chopping throw. This method is also valid for reducing data taken by the chopping with insufficient frequency. In this paper we will report the details of the weighted average method and demonstrate its performance against practical observing data.
MIMIZUKU is the first-generation mid-infrared instrument for the university of Tokyo Atacama Observatory (TAO) 6.5-m telescope. MIMIZUKU provides imaging and spectroscopic monitoring capabilities in a wide wavelength range from 2 to 38 μm, including unique bands like 2.7-μm and 30-μm band. Recently, we decided to add spectroscopic functions, KL-band mode (λ= 2.1-4.0 μm; R =λ/Δλ ~ 210) and 2.7-μm band mode ( λ= 2.4-2.95 μm; R ~ 620), and continuous spectroscopic coverage from 2.1 to 26 μm is realized by this update. Their optical designing is completed, and fabrications of optical elements are ongoing. As recent progress, we also report the completion of the cryogenic system and optics. The cryogenic system has been updated by changing materials and structures of thermal links, and the temperatures of the optical bench and detector mounting stages finally achieved required temperatures. Their stability against instrument attitude is also confirmed through an inclination test. As for the optics, its gold-plated mirrors have been recovered from galvanic corrosion by refabrication and reconstruction. Enough image quality and stability are confirmed by room-temperature tests. MIMIZUKU is intended to be completed in this autumn, and commissioning at the Subaru telescope and scientific operations on the TAO telescope are planned in 2017 and around 2019, respectively. In this paper, these development activities and future prospects of MIMIZUKU are reported.
Simultaneous-color Wide-field Infrared Multi-object Spectrograph, SWIMS, is one of the first generation instruments for University of Tokyo Atacama Observatory 6.5m Telescope where almost continuous atmospheric window from 0.9 to 2.5μm appears, thanks to the high altitude and dry climate of the site. To utilize this excellent condition, SWIMS is capable of simultaneous two-color imaging with a field of view of 9’. in diameter and λ/Δλ ~1000 multi-object spectroscopy at 0.9–2.5μm in a single exposure, utilizing a dichroic mirror inserted in the collimated beam. Here, we overview the instrument, report results of its full-assembly tests in the laboratory and present the future plan.
MIMIZUKU is a mid-infrared imager and spectrograph being developed for the University of Tokyo Atacama Observatory (TAO) 6.5-m telescope (PI: Y. Yoshii). To fully utilize a high atmospheric transmission of the Chajnantor site, MIMIZUKU covers a wide wavelength range from 2 to 38 μm with three array detectors: a HAWAII-1RG HgCdTe 1024 × 1024 array with a 5 μm cutoff manufactured by Teledyne, an Aquarius Si:As IBC 1024 × 1024 array by Raytheon, and a MF-128 Si:Sb BIB 128 × 128 array by DRS. We have newly developed an array controller system to operate these multiple arrays. A sampling rate higher than 0.5 MHz is required to prevent from saturation of their wells in broad-band imaging observations with MIMIZUKU due to high thermal background flux. Such high speed signals are dulled when passing through lines from the arrays to readout circuits. To overcome this problem, we have developed high-speed cryogenic buffer pre-amplifier circuits with commercial GaAs MESFETs, instead of Si JFETs, which are generally used in buffer amplifiers at cryogenic temperatures. The cryogenic buffer circuits are installed on an outer wall of the optical bench of MIMIZUKU at 20 K. We have measured readout noises of the array controller system including the cryogenic buffers in a test cryostat and room temperature circuits and confirmed that input referred noises of the system are lower than the specification value of the readout noise of the Aquarius array.
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.
Strong time variation of atmospheric transmittance is a crucial problem for monitoring observations at mid- infrared wavelengths from the ground. To overcome this problem, a new device called "Field Stacker" has been developed. It is an optical device to combine two discrete fields in the telescope FoV into a single field and feed it in the camera. It enables us to observe a science target and a reference star simultaneously, and improve the photometric accuracy dramatically based on real-time calibration. To practically achieve highly accurate photometry, the tilt of the mirrors in the Field Stacker should be accurately adjusted. Acceptable error of the misalignment of each pick-up mirror is estimated to be < 0.0085 deg from a simple geometric calculation. The actual tilt error measured in the laboratory almost met this requirement. Spatial variation of the water vapor in the atmosphere is another concern for the accurate photometry. Assuming a simple model of the atmospheric structure, the spatial variation was estimated from time variation of infrared background radiation. The estimated variation of the water vapor was 0.00036 mm within the telescope FoV (Φ25 arc- minutes), suggesting that it does not significantly affect the photometric accuracy even at 31 and 37 μm. Number density of reference stars was examined based on all-sky infrared catalogues to estimate the availability of the Field Stacker. The estimated availabilities at 9 and 18 μm were 99.8% and 58.8%, respectively.
Anti-reflection (AR) is very important for high-throughput optical elements. The durability against cooling is
required for the AR structure in the cryogenic optics used for mid-infrared astronomical instruments. Moth-eye structure is a promising AR technique strong against cooling. The silicon lens and grism with the moth-eye structure are being developed to make high-throughput elements for long-wavelength mid-infrared instruments. A double-sided moth-eye plano-convex lens (Effective diameter: 33 mm, Focal length: 188 mm) was fabricated. By the transmittance measurement, it was confirmed that its total throughput is 1.7± 0.1 times higher than bare silicon lenses in a wide wavelength range of 20{45 μm. It suggests that the lens can achieve 83±5% throughput in the cryogenic temperature. It was also confirmed that the moth-eye processing on the lens does not modify the focal length. As for the grism, the homogeneous moth-eye processing on blaze pattern was realized by employing spray coating for the resist coating in EB lithography. The silicon grism with good surface roughness was also developed. The required techniques for completing moth-eye grisms have been established.
Simultaneous Color Wide-field Infrared Multi-object Spectrograph, SWIMS, is one of the first generation in- struments for the University of Tokyo Atacama Observatory (TAO) 6.5m Telescope now under construction. A dichroic mirror being inserted in the collimated beam, it is capable of two-color simultaneous imaging with FoV
of 9:16φ or R ∼ 1000 multi-object spectroscopy at 0.9–2.5μm wavelength range in one shot, and enables us to
carry out efficient NIR imaging/spectroscopic survey of objects such as distant galaxies and young stellar objects.
All the major components have been fabricated and we will start integration and laboratory cool-down test in the summer of 2014. After the engineering and initial science observations at the Subaru telescope, SWIMS will be transported to TAO telescope and see the first light in 2018.
We report the restraint deformation and the corrosion protection of gold deposited aluminum mirrors for mid-infrared
instruments. To evaluate the deformation of the aluminum mirrors by thermal shrinkage, monitoring measurement of the
surface of a mirror has been carried out in the cooling cycles from the room temperature to 100 K. The result showed
that the effect of the deformation was reduced to one fourth if the mirror was screwed with spring washers.
We have explored an effective way to prevent the mirror from being galvanically corroded. A number of samples have
been prepared by changing the coating conditions, such as inserting an insulation layer, making a multi-layer and overcoating
water blocking layer, or carrying out precision cleaning before coating. Precision cleaning before the deposition
and protecting coat with SiO over the gold layer seemed to be effective in blocking corrosion of the aluminum. The SiO
over-coated mirror has survived the cooling test for the mid-infrared use and approximately 1 percent decrease in the
reflectance has been detected at 6-25 microns compared to gold deposited mirror without coating.
The MIMIZUKU is the first-generation mid-infrared instrument for the TAO 6.5-m telescope. It challenges to prove the origin of dust and the formation of planets with its unique capabilities, wide wavelength coverage and precise calibration capability. The wide wavelength coverage (2-38 μm) is achieved by three switchable cameras, NIR, MIR-S, and MIR-L. The specifications of the cameras are revised. A 5μm-cutoff HAWAII-1RG is decided to be installed in the NIR camera. The optical design of the MIR-L camera is modified to avoid detector saturation.
Its final F-number is extended from 5.2 to 10.5. With these modifications, the field of view of the NIR and MIR-L camera becomes 1.2’ × 1.2’ and 31” × 31”, respectively. The sensitivity of each camera is estimated based on the
revised specifications. The precise calibration is achieved by the “Field Stacker” mechanism, which enables the simultaneous observation of the target and the calibration object in different fields. The up-and-down motion
of the cryostat (~ 1 t), critical for the Field Stacker, is confirmed to have enough speed (4 mm/s) and position accuracy (~ 50 μm). A control panel for the Field Stacker is completed, and its controllers are successfully
installed. The current specifications and the development status are reported.
ANIR (Atacama Near InfraRed camera) is a near infrared camera for the University of Tokyo Atacama 1.0m telescope installed at the summit of Co. Chajnantor (5640m altitude) in northern Chile. The high altitude and the extremely low water vapor (precipitable water vapor:PWV=0.5mm) of the site enables us to perform observation of hydrogen Paschen alpha (Paα) emission line at 1.8751 μm. Since the first light observation in June 2009, we have succesfully obtained Paα narrow-band images of Galactic objects and near-by Galaxies. However, as there are many atmospheric absorption features within the wavelength range of the narrow-band filters which vary temporally due to change of PWV, it is difficult to calibrate the emission line flux accurately. Therefore, we have developed a new method to restore Paα emission-line flux from ground-based narrow-band filter imaging observations. First, average atmospheric transmittance within the narrow-band filter is derived using 2MASS stars in a image. Second, PWV is then estimated by comparing the transmittance with that calculated by atmospheric transmittance model software, ATRAN. Finally, the atmospheric transmittance at the wavelength of Paα emission-line is obtained from the model atmosphere corresponding to the obtained PWV. By applying this method to the data of nearby Luminous Infrared Galaxies obtained by ANIR, the emission line strength is estimated within the accuracy of 10% relative to that observed by HST/NICMOS. In this paper, we describe details of the calibration method and its accuracy.
We have evaluated on-sky performances of a mid-infrared camera MAX38 (Mid-infrared Astronomical eXploerer)
on the miniTAO 1-meter telescope. A Strehl ratio at the N-band is estimated to be 0.7-0.8, and it reaches to 0.9
at the 37.7 micron, indicating that diffraction limited angular resolution is almost achieved at the wavelength
range from 8 to 38 micron. System efficiencies at the N and the Q-band are estimated with photometry of
standard stars. The sensitivity at the 30 micron cannot be exactly estimated because there are no standard stars
bright enough. We use the sky brightness instead. The estimated efficiencies at the 8.9, 18.7, and 31.7 micron
are 4%, 3%, 15% , respectively. One-sigma sensitivity in 1 sec integration of each filter is also evaluated. These
give good agreements with the designed values. Preliminary scientific results are briefly reported.
TAO (The University of Tokyo Atacama Observatory) is planned to be constructed at the summit of Co. Chajnantor (5640 m altitude) in Chile. MIMIZUKU (Mid-Infrared Multi-field Imager for gaZing at the UnKnown Universe) is a mid-infrared imager (Field of View: 1' x 1'- 2' x 2') and spectrometer (Δλ/λ: 60-230) for the 6.5-m TAO telescope, covering the wavelength range of 2-38 μm. The MIMIZUKU has a unique equipment called Field Stacker (FS) which enables the simultaneous observation of target and reference object. The simultaneity is expected to improve photometric accuracy and to realize long-term monitoring observations. The development status of the MIMIZUKU is reported in this paper. The FS and the cryostat of the MIMIZUKU have been fabricated and under testing. The cold optics (550 mm x 750 mm x 2 floors) with 28 mirrors has been constructed. The mirrors were aligned with the positional precision of 0.1 mm and the angular precision of 0.1 deg. The evaluated optical performance is that the diffraction-limited image at λ <8 μm and the enough compact image (r <2 pix=0.22") at 2 λ ~2μm can be obtained. In the cold optics, the drive systems with backlash-less gears are employed and work well even in cryogenic environment. The grisms made with silicon and germanium have been fabricated by ultraprecision cutting. It was found that their surface roughness, grating constant, and blaze angle almost measure up to the designed values.
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.
Thirty micron has remained one of unexplored frontiers of ground-based astronomical observations. Recent developments of extreme high sites including the Chajnantor TAO site (5,640m) enable us to access the this wavelengths from the ground. The expected transmittance seems clear enough for astronomical observations, but practical evaluations based on astronomical data has not been carried out yet. We have analyzed images obtained at the 31.7 micron with a mid-infrared camera MAX38 attached on a mini-TAO 1.0-meter telescope. 109 images of a star IRC+10420 and 11,114 images of the sky have been reduced. Clear relationship between the measured photocurrents and the perceptible water vapor has been found. Simple estimation of the photocurrents with of the ATRAN model gives good agreements with the measurements, indicating that the ATRAN model reproduce the atmospheric transmittance reasonably well. This also supports our assumption that the scaling factor 0.85 of the PVW at the Chajnantor TAO site to the PWV at the APEX. The average transmittance in the 31.7 micron is achieved to be over 20% when the PWV below 0.6 mm. In some cases clear degradation up to 10% in the transmittance is found. It may be caused by droplets of liquid or iced water with a size over 10 micron although the causes are not exactly specified. Diurnal time variations of the sky photocurrents are also investigated. The sky is sometimes bright and usually unstable in the twilight time. On the other hand the sky around the noontime does not show clear difference from the night sky. It may suggest that the observing condition at the thirty micron windows remain good even in the daytime.
A metal mesh filter is appropriate to a band-pass filter for astronomy in the long mid-infrared between 25 and 40 μm,
where most of optical materials are opaque. The mesh filter does not require transparent dielectric materials unlike
interference filters because the transmission characteristics bare determined by surface plasmon-polariton (SPP)
resonances excited on a metal surface with a periodic structure. In this study, we have developed the mesh filters
optimized to atmospheric windows at 31.8 and 37.5 μm accessible from the Chajnantor site of 5,640 m altitude. First,
mesh filters made of a gold film of 2 μm thickness have been fabricated. Four identical film-type filters are stacked
incoherently to suppress leakages at stop-bands. The transmissions of the stacked filters have been measured to be 0.8 at
the peaks and below 1 x 10-3 at the stop-bands at 4 K. The ground-based mid-infrared camera MAX38 has been equipped
with the stacked filters and successfully obtained diffraction-limited stellar images at the Chajnantor site. The film-type
mesh filter does not have sufficient mechanical strength for a larger aperture and for use in space. We have developed
mesh filters with higher strength by applying the membrane technology for x-ray optics. The membrane-type mesh filter
is made of SiC and coated with a thin gold layer. The optical performance of the mesh filter is independent of internal
materials in principle because the SPP resonances are excited only on the metal surface. The fabricated membrane-type
mesh filter has been confirmed to provide comparable optical performance to the film-type mesh filter.
We have been developing high-throughput optical elements with the moth-eye structures for mid-infrared optical
systems. The moth-eye structures are optimized for the wavelength of 25-45μm. It consists of cones with a
height of 15-20μm arranged at an interval of 5μm. They are formed on silicon substrate by electron-beam
lithography and reactive ion etching. As a verification of the usefulness of moth-eye, a double-sided moth-eye
silicon plane was fabricated. It shows a transmittance increase of 60% compared with the unprocessed silicon
plane. As the first trial of the moth-eye optical element, two silicon lenses with single-sided moth-eye were
fabricated. One is a plane-convex lens with the moth-eye on the convex surface. The size of the moth-eye
formed region is 30 mm x 30 mm. Its focal length is 186 mm. The other one is a biconvex lens with moth-eye
formed region of Φ 33 mm and a focal length of 94 mm. Uniform moth-eye pattern was fabricated especially
for the second lens sample. Imaging test with the first sample showed that neither image degradation nor focal
length variation was induced by the moth-eye fabrication. As a step to grism with moth-eye, a moth-eye grating
sample was fabricated. The grating pattern (Grating constant: 124.9μm, Blaze angle: 4 deg) was successfully
fabricated with anisotropic etching. Moth-eye patterns were fabricated on the grating surface. Although the
resulted moth-eye was successfully fabricated in the most regions, some non-uniformity was found. It can be
attributed to unevenness of resist coating, and improvement of coating method is needed.
Mid-infrared, 25 - 45 microns, is a very important wavelength region to investigate the physics of lower temperature
environments in the universe. There are few transparent materials in the range of mid-infrared except
silicon. However, the reflection on a silicon surface reaches 30 % because of its high refractive index (~3.4).
To apply silicon to mid-infrared astronomical instruments, we need a way of antireflection and have adopted
a moth-eye structure. This structure keeps durable under cryogenic environments, which is advantageous to
mid-infrared instruments. We have fabricated three samples of the moth-eye structure on plane silicon surfaces
by electron-beam photo-lithograph and reactive ion etching. The structures consist of many cones standing on
silicon surfaces. We have substantiated the transmittance of 96 % or higher in the wide range of 20 - 50 microns
and higher than 98 % at the maximum. The transmittance of moth-eye surfaces, however, is theoretically expected
as 100 %. We have examined the discrepancy between the transmittance of the theory and fabrications
with electromagnetic simulations. It has been revealed that shapes of the cones and gaps at the bottom of the
cones seriously affect the transmittance. We have estimated a few tolerances for manufacturing the moth-eye
structures achieving sufficient transmittance of nearly 100 %.
We successfully carried out 30-micron observations from the ground-based telescope for the first time with our newly
developed mid-infrared instrument, MAX38, which is mounted on the University of Tokyo Atacama 1.0-m telescope
(miniTAO telescope). Thanks to the high altitude of the miniTAO (5,640m) and dry weather condition of the Atacama
site, we can access the 30-micron wavelength region from ground-based telescopes. To achieve the observation at 30-
micron wavelength, remarkable devices are employed in MAX38. First, a Si:Sb 128x128 array detector is installed
which can detect long mid-infrared light up to 38-micron. Second, we developed metal mesh filters for 30-micron region
band-pass filter, which are composed of several gold thin-films with cross-shaped holes. Third, a cold chopper, a 6-cm
square plane mirror controlled by a piezoelectric actuator, is built into the MAX38 optics for canceling out the
atmospheric turbulence noise. It enables square-wave chopping with a 50-arcsecound throw at a frequency more than 5-
Hz. Finally, a low-dispersion grism spectrometer (R~50) will provide information on the transmission spectrum of the
terrestrial atmosphere in 20 to 40 micron. In this observation, we clearly demonstrated that the atmospheric windows
around 30-micron can be used for the astronomical observations at the miniTAO site.
Ground-based mid-infrared observations have two distinct advantages over space observations despite relatively lower
sensitivity. One is the high spatial resolution and the other is the monitoring capability. These advantages can be
emphasized particularly for the next coming ground-based infrared project University of Tokyo Atacama Observatory
(TAO). Thanks to the low water vapor of the TAO site (5,640m) and the large aperture of the telescope (6.5meter), we
can observe at 30 micron with a spatial resolution of 1 arcsec. It is about ten times higher than that of current space
telescopes. The TAO is also useful for monitoring observations because of the ample observing time.
To take these advantages we are now developing a new mid-infrared infrared instrument for the TAO 6.5-meter
telescope. This covers a wide wavelength range from 2 to 38 micron with three detectors (Si:As, Si:Sb, and InSb).
Diffraction limited spatial resolution can be achieved at wavelengths longer than 7 micron. Low-resolution spectroscopy
can also be carried out with grisms. This instrument equips a newly invented "field stacker" for monitoring observations.
It is an optical system that consists of two movable pick-up mirrors and a triangle shaped mirror, and combine two
discrete fields of the telescope into camera's field of view. It will enable us to apply a differential photometry method
and dramatically improve the accuracy and increase the feasibility of the monitoring observations at the mid-infrared
wavelengths.
We have developed a near infrared camera called ANIR (Atacama Near InfraRed camera) for the University of
Tokyo Atacama 1.0m telescope installed at the summit of Co. Chajnantor (5640m altitude) in northern Chile.
The camera is based on a PACE HAWAII-2 array with an Offner relay optics for re-imaging, and field of view
is 5.
3 × 5.
3 with pixel scale of 0.
31/pix. It is also capable of optical/infrared simultaneous imaging by inserting
a dichroic mirror before the focal plane. The high altitude and extremely low water vapor (PWV=0.5mm) of
the site enables us to perform observation of hydrogen Paschenα (Paα) emission line at 1.8751 μm. The first
light observation was carried out in July 2009, and we have successfully obtained Paα images of the Galactic
center using the N1875 narrow-band filter. This is the first success of Paα imaging of a Galactic object from a
ground based telescope. System efficiencies for the broad-band filters are measured to be 15% at the J-band and
30% at Ks, while that of the N1875 narrow-band filter, corresponding to Paα; wavelength, varies from 8 to 15%,
which may be caused by fluctuation of the atmospheric transmittance. ATRAN simulation suggests that this
corresponds to PWV of 0.3 - 1.5mm, consistent with previous results of the site testing. Measured seeing size
is median ~0.
8, corresponding to the real seeing value of 0.
6 - 0.
8. These results demonstrates the excellent
capability of the site for infrared observations.
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.