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SPIE Future Sensing Technologies 2023 2023年5月22日
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Astronomical Optics: Design, Manufacture, and Test of Space and Ground Systems III 2021年8月24日
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Proceedings of SPIE - The International Society for Optical Engineering 11815 2021年This work reviews the search for extraterrestrial life signatures with a special focus on the fluorescence microscope that we have been developing for the life-signature search on Mars and other sites. The surface and subterranean Mars, clouds of Venus, the Moon, asteroids, icy bodies, such as the moons of Jupiter and Saturn, and so on are important sites for life-signature exploration in the solar system. One possible exploration strategy is to target characteristics similar to those in terrestrial life, such as microorganisms with metabolic activity and similar uniform small structures microbes surrounded by a membrane that primarily comprise carbon-based molecules. These characteristics can be analyzed with fluorescence microscopy, which has a high spatial resolution and employs a combination of fluorescent pigments to distinguish microbial properties. Following an introduction, the life signature search and astrobiological analysis of the targeted characteristics are discussed. The extraterrestrial life exploration methods using a microscope are described. Also, other methods, including mass spectrometry, the sterilization-and-comparison method (detection of ability to die), proliferation, and analysis of shape, color, growth, or movement, are discussed. Lastly, we overview the life-signature detection fluorescence microscope that we have been developing, and present the Bread Board Model of it.
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SPACE TELESCOPES AND INSTRUMENTATION 2020: ULTRAVIOLET TO GAMMA RAY 11444 2021年Many Earth-sized planets have been discovered and some of them are potentially in the habitable zone. In addition, several Earth-sized planets have been detected around low temperature stars near our solar system. However, it is difficult to characterize them as Earth-like or Venus-like, even though they are relatively very close to our solar system. We performed a conceptual design of an Ultraviolet Spectrograph for Exoplanet (UVSPEX) for World Space Observatory Ultraviolet (WSO-UV), which is 1.7-m UV space telescope being prepared by Russia. The spectral range is to exceed wavelengths from 115 nm to 135 nm to detect at least H Lyman alpha 121.6nm to O I 130 nm. The throughput is >4%. UVSPEX is planned to be a part of a Field Camera Unit (FCU). This additional instrument would enable us to observe similar to 20 Earth-like exoplanets and detect an oxygen exosphere if some of them have an Earth-like atmosphere.
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Proceedings of SPIE - The International Society for Optical Engineering 11353 2020年We present a life detection fluorescence microscope (LDM) for near-future Solar System exploration. The search for extra-terrestrial life in the Solar System is considered a crucial issue in space science. Previously, the NASA Viking mission conducted some life science experiments on Mars in 1976. Other exploration missions have increased our knowledge of Mars. Nevertheless, the presence of life on Mars has not yet been conclusively demonstrated. The LDM uses fluorescence pigments and an excitation light source to identify biological cells, coupled to a microscope for imaging of fluorescent cells. An optical design for this compact microscope is presented herein. We discuss the application of this LDM both for Mars soils and regolith and other targets in the Solar System.
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Trans. JSASS Aerospace Tech. Japan 17(17) 234-243 2019年 査読有り
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Proceedings of SPIE - The International Society for Optical Engineering 10706 2018年©2018 SPIE. Utilized in exploration missions of the solar system. The primary objective of the high-contrast baffle is to reveal atmospheric escape on Mars, while other faint objects around bright sources are potential targets. We diverted heritages studied for exoplanet science and instrumentation to this work. The apodization in this study is realized by an edge with microscopic Gaussian-shaped structures. Simulations confirmed the concept and design of the high-contrast apodization baffle and a lab-scale prototype baffle was manufactured, which comprised a transparent flat substrate and a thin film of aluminum. The experiment was executed using a He-Ne laser with a wavelength of 633 nm. The results obtained show that the apodization by the Gaussian-shaped structure significantly improves the contrast. Achieved contrast is better than 10-6.5and 10-8 at > 0.5° and ? > 1°,respectively, and satisfy the requirement for remote sensing of atmospheric escape on Mars.
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APPLIED OPTICS 56(23) 6694-6708 2017年This paper demonstrates a cryogenic deformable mirror (DM) with 1020 actuators based on micro-electrical mechanical systems (MEMS) technology. Cryogenic space-borne infrared telescopes can experience a wavefront error due to a figure error of their mirror surface, which makes the imaging performance worse. For on-orbit wavefront correction as one solution, we developed aMEMS-processed electro-static DM with a special surrounding structure for use under the cryogenic temperature. We conducted a laboratory demonstration of its operation in three cooling cycles between 5 K and 295 K. Using a laser interferometer, we detected the deformation corresponding to the applied voltages under the cryogenic temperature for the first time. The relationship between voltages and displacements was qualitatively expressed by the quadratic function, which is assumed based on the principle of electro-static DMs. We also found that it had a high operating repeatability of a few nm root-meansquare and no significant hysteresis. Using the measured values of repeatability, we simulated the improvement of the point spread function (PSF) by wavefront correction with our DM. These results show that our developed DM is effective in improving imaging performance and PSF contrast of space-borne infrared telescopes. (C) 2017 Optical Society of America
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MATERIAL TECHNOLOGIES AND APPLICATIONS TO OPTICS, STRUCTURES, COMPONENTS, AND SUB-SYSTEMS III 10372 2017年A large-scale lightweight mirror that is made of silicon carbide-based material is required for the coming astronomical and earth observation missions. The influence of the inhomogeneity of the coefficient of thermal expansion (CTE) on specular surface accuracy was studied as an important technological issue for such a large optical component. At first, a systematic case study for the series of CTE's main factors was conducted using the finite element method, and consequently a comprehensive equation to calculate the amount of surface deviation was derived. Based on that technology, finite element analysis to simulate the surface accuracy profile that a test mirror sample showed during cryogenic measurement was carried out using experimentally obtained CTE data from cutout test pieces, and the profile was successfully reproduced.
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Proceedings of SPIE - The International Society for Optical Engineering 10568 2017年Light-weight mirrors are developed for two Japanese infrared astronomical missions, ASTRO-F and SPICA. ASTRO-F is scheduled for launch in 2005, while the target year for launch of SPICA is 2010. The mirrors of the ASTRO-F telescope are made of a sandwich-type silicon carbide (SiC) material, comprising porous core and CVD coat of SiC on the surface. Cryogenic measurements of the ASTRO-F primary mirror and telescope assembly were performed extensively. As for the SPICA telescope, which has an aperture of 3.5-m diameter, carbon-fiber-reinforced SiC (C/SiC composite), as well as SiC, is one of the promising candidates for mirror material. C/SiC composite spherical test mirrors of 160-mm diameter has recently been manufactured and tested. This paper presents the experimental results of the cryogenic performance obtained for the sandwich-type SiC mirrors and the C/SiC composite mirrors.
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JOURNAL OF MATERIALS ENGINEERING AND PERFORMANCE 23(3) 850-858 2014年3月The Japan Aerospace Exploration Agency has studied large-scale, lightweight mirrors constructed of SiC-based materials as a key technology for future earth observations and astronomical missions. One of the most important technical issues for large-scale ceramic components is their quality stability (viz., differences in material properties depending on the part and the processing), which might influence the structural and/or thermal reliability through unforeseen deformation and breakage. In this study, the authors used a simple, low-cost method for evaluating the properties of SiC mirror materials. Using mechanical testing, thermodilatometry, and microstructural analysis on samples cut from the periphery of a prototype 800-mm-diameter mirror body, the overall quality of the mirror body material was determined.
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Proceedings of SPIE - The International Society for Optical Engineering 9143 2014年 査読有りWe present the design, fabrication and test results for a dichroic mirror, which was primarily developed for the SPICA Coronagraph Instrument (SCI), but is potentially useful for various types of astronomical instrument. The dichroic mirror is designed to reflect near- and mid-infrared but to transmit visible light. Two designs, one with 3 layers and one with 5 layers on BK7 glass substrates, are presented. The 3-layer design, consisting of Ag and ZnS, is simpler, and the 5-layer design, consisting of Ag and TiO< inf> 2< /inf> is expected to have better performance. Tape tests, evaluation of the surface figure, and measurements of the reflectivity and transmittance were carried out at ambient temperature in air. The reflectivity obtained from measurements made on mirrors with 5 layers were < 80 % for wavelengths, λ, from 1.2 to 22 μm and < 90 % for λ from 1.8 to 20 μm. The transmittance obtained from measurements made on mirrors with 5 layers were < 70 % for λ between 0.4 and 0.8 μm. Optical ghosting is estimated to be smaller than 10< sup> -4< /sup> at λ < 1.5 μm. A protective coating for preventing corrosion was applied and its influence on the reflectivity and transmittance evaluated. A study examining the trade-offs imposed by various configurations for obtaining a telescope pointing correction signal was also undertaken.
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Proceedings of SPIE - The International Society for Optical Engineering 9151 2014年 査読有りIn this report we describe our development of a prototype inverse-polished mirror for the passive correction of the static and predictable wavefront errors (WFE) of space-based telescopes, in particular, especially for infrared coronagraphs. An artificial WFE pattern with a root mean square (rms) value of 350 nm was numerically generated to facilitate the design of the prototype mirror. The surface of the mirror is approximately flat, is 50.0 mm in diameter and 15.0 mm thick at the edge. The designed WFE pattern was constructed on the mirror surface by micro-polishing. Both the figure and roughness of the mirror surface were evaluated. The rms value of the measured surface figure was reduced to 135 nm after subtraction of the designed surface figure. The benefit of subtraction to mid-infrared coronagraph performance was simulated, which showed the contrast was improved by a factor of ∼100 close to the core (closer than 10 λ/D where λ and D are the wavelength and telescope aperture diameter, respectively) of the coronagraphic image of a point source. An analysis of the power spectrum density shows that the lower frequencies in the WFE are well reproduced on the mirror, while the higher frequencies remain due to the limitations imposed on the controllable spatial resolution by the fabrication process. In this study, inverse-polished mirrors combined with deformable mirrors and their application to ground-based telescopes are also discussed. To fully explore the potential of the inverse-polished mirror, a systematic allocation of the error budget is essential taking into account not only the fabrication accuracy of the mirror but also an evaluation of the telescope and other factors with non-predictable uncertainties.
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INFRARED REMOTE SENSING AND INSTRUMENTATION XXII 9219 2014年We present the concept, design, fabrication, and evaluation of a new deformable mirror (DM), which is latchable, compact, and designed to be applicable for cryogenic environments. The main body of a prototype DM was fabricated from a monolithic cuboid of aluminum using wire electrical discharge machining (EDM). A flexible structure was constructed inside the block by 3-dimensionally crossed hollowing using the EDM. The prototype has 6 x 6 channels, and its volume is 27 mm x 27 mm x 30 mm. The mirror was formed on the surface of the aluminum block using a high-precision NC lathe. The surface figure of the mirror was evaluated and 34 nm rms was obtained. The evaluated surface roughness for the center and off-center areas of the mirror was 9.2 nm rms and 7.6 nm rms, respectively Screws set at the back of the block deform the mirror via springs and the internal flexible structure. We present our first demonstration of deformation of the mirror carried out at ambient temperature. The relationship between the displacement of the screws and the deformation of the mirror was evaluated. Consequently, a linear relationship was confirmed, and no significant hysteresis was found. The application of such mirrors to telescopes used for various different objectives is discussed. We conclude that a DM based on our concept can be used for wavefront correction of space-borne telescopes, especially in the infrared wavelength region.
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SPACE TELESCOPES AND INSTRUMENTATION 2014: OPTICAL, INFRARED, AND MILLIMETER WAVE 9143 2014年SPICA (Space Infrared Telescope for Cosmology and Astrophysics) is an astronomical mission optimized for mid-and far-infrared astronomy with a 3-m class telescope which is cryogenically cooled to be less than 6 K. The SPICA mechanical cooling system is indispensable for the mission but, generates micro-vibrations which could affect to the pointing stability performances. Activities to be undertaken during a risk mitigation phase (RMP) include consolidation of micro-vibration control design for the satellite, as well as a number of breadboarding activities centered on technologies that are critical to the success of the mission. This paper presents the RMP activity results on the micro-vibration control design.
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NOVEL OPTICAL SYSTEMS DESIGN AND OPTIMIZATION XVII 9193 2014年We present the development of wideband spectral dispersers of which the primary scientific objective is the characterization of the atmospheres of exoplanets, including the challenge of detecting biomarkers. A disperser comprising a prism with a grating pattern on its surface provides simultaneous wideband coverage with low spectral resolution (R = 300). The optics is simple, compact, and contains no moving parts. A comparative study of 21 materials for the disperser was carried out for use in the optical, near-infrared, and mid-infrared wavelength regions. KRS-5, CdZnTe, ZnS LiF, Sapphire, and S-TIH11 were selected, and designs of the optics for single-channel wideband spectrometers using the selected six materials were considered. Then, trial designs of the multi-channel spectrometers were carried out taking the properties of the detectors into consideration. The 3-channel design covers the wavelength region of similar to 0.2-23 mu m using a CCD detector, an InSb detector, and a Si: As detector. The 2-channel design covers similar to 0.4-23 mu m using a HgCdTe detector and a Si: As detector. A fabricated ZnS disperser is shown together with a CsI subprism which compensates for the optical axis. The application of defocusing, high dispersion spectroscopy, extension to the UV wavelength region, and the combination of the disperser with future space telescopes are discussed.
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APPLIED OPTICS 52(26) 6458-6466 2013年9月 査読有りThe authors studied the quality evaluation technology of a spaceborne large-scale lightweight mirror that was made of silicon carbide (SiC)-based material. To correlate the material property of a mirror body and the mirror accuracy, the authors evaluated the mirror surface deviation of a prototype mirror by inputting actually measured coefficient of thermal expansion (CTE) data into a finite element analysis model. The CTE data were obtained by thermodilatometry using a commercial grade thermal dilatometer for the samples cut from all over the mirror surface. The computationally simulated contour diagrams well reproduced the mirror accuracy profile that the actual mirror showed in cryogenic testing. Density data were also useful for evaluating the mirror surface deviation because they had a close relationship with the CTE. (c) 2013 Optical Society of America
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Applied optics 52(26) 6458-6466 2013年9月 査読有り
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APPLIED OPTICS 52(20) 4797-4805 2013年7月 査読有りThe Japan Aerospace Exploration Agency has studied a large-scale lightweight mirror constructed of reaction-bonded silicon carbide-based material as a key technology in future astronomical and earth observation missions. The authors selected silicon carbide as the promising candidate due to excellent characteristics of specific stiffness and thermal stability. One of the most important technical issues for large-scale ceramic components is the uniformity of the material's property, depending on part and processing. It might influence mirror accuracy due to uneven thermal deformation. The authors conducted systematic case studies for the conditions of CTE by finite element analysis to know the typical influence of material property nonuniformity on mirror accuracy and consequently derived a comprehensive empirical equation for the series of CTE's main factors. In addition, the authors computationally reproduced the mirror accuracy profile of a small prototype mirror shown in cryogenic testing and hereby verified wide-range practical computational evaluation technology of mirror accuracy. (C) 2013 Optical Society of America
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Applied optics 52(20) 4797-4805 2013年7月 査読有り
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Astronomy and Astrophysics 550 2013年Context. Little is known about the properties of the warm (T ≳ 150 K) debris disk material located close to the central star, which has a more direct link to the formation of terrestrial planets than does the low-temperature debris dust that has been detected to date. Aims. To discover new warm debris disk candidates that show large 18 μm excess and estimate the fraction of stars with excess based on the AKARI/IRC Mid-Infrared All-Sky Survey data. Methods. We searched for point sources detected in the AKARI/IRC All-Sky Survey, which show a positional match with A-M dwarf stars in the Tycho-2 Spectral Type Catalogue and exhibit excess emission at 18 μm compared to what is expected from the K magnitude in the 2MASS catalogue. Results. We find 24 warm debris candidates including 8 new candidates among A-K stars. The apparent debris disk frequency is estimated to be 2.8 ± 0.6%. We also find that A stars and solar-type FGK stars have different characteristics of the inner component of the identified debris disk candidates. While debris disks around A stars are cooler and consistent with steady-state evolutionary model of debris disks, those around FGK stars tend to be warmer and cannot be explained by the steady-state model. © 2013 ESO. dust S
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MATERIAL TECHNOLOGIES AND APPLICATIONS TO OPTICS, STRUCTURES, COMPONENTS, AND SUB-SYSTEMS 8837 2013年Owing to its high specific stiffness and high thermal stability, silicon carbide is one of the materials most suitable for large space-borne optics. Technologies for accurate optical measurements of large optics in the vacuum or cryogenic conditions are also indispensable. Within the framework of the large SiC mirror study program led by JAXA, we manufactured an 800-mm-diameter lightweight telescope, all of which is made of HB-Cesic, a new type of carbon-fiberreinforced silicon carbide (C/SiC) material developed jointly by ECM, Germany and MELCO, Japan. We first fabricated an 800-mm HB-Cesic primary mirror, and measured the cryogenic deformation of the mirror mounted on an HB-Cesic optical bench in a liquid-helium chamber. We observed the cryo-deformation of 110 nm RMS at 18 K with neither appreciable distortion associated with the mirror support nor significant residual deformation after cooling. We then integrated the primary mirror and a high-order aspheric secondary mirror into a telescope. To evaluate its optical performance, we established a measurement system, which consists of an interferometer in a pressure vessel mounted on a 5-axis adjustable stage, a 900-mm auto-collimating flat mirror, and a flat mirror stand with mechanisms of 2-axis tilt adjustment and rotation with respect to the telescope optical axis. We installed the telescope with the measurement system into the JAXA 6-m chamber and tested them at a vacuum pressure to verify that the system has a sufficiently high tolerance against vibrations in the chamber environment. Finally we conducted a preliminary study of sub-aperture stitching interferometry, which is needed for telescopes of our target missions in this study, by replacing the 900-mm flat mirror with a rotating 300-mm flat mirror.
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Proceedings of SPIE - The International Society for Optical Engineering 8837 2013年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. © 2013 SPIE.
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GROUND-BASED AND AIRBORNE INSTRUMENTATION FOR ASTRONOMY IV 8446 2012年A mid-infrared (MIR) imager and spectrometer is being investigated for possible construction in the early operation of the Thirty Meter Telescope (TMT). Combined with the MIR adaptive optics (AO) system (MIRAO), the instrument will afford similar to 15 times higher sensitivity and similar to 4 times better spatial resolution (0.07") at 10 mu m compared to 8m-class telescopes. Additionally, through exploiting the large collection area of the TMT, the high-dispersion spectroscopy mode will be unrivaled by other ground-and space-based facilities. These combined capabilities offer the possibility for breakthrough science, as well as 'workhorse' observing modes of imaging and low/moderate spectral resolution. In this paper we summarize the primary science drivers that are guiding the instrument design.
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Proceedings of SPIE - The International Society for Optical Engineering 8442 2012年We present the current status of the development of the SPICA Coronagraph Instrument (SCI). SPICA is a nextgeneration 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 groundbased 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 highthroughput binary mask coronagraph, will be presented. Furthermore, we will show that SCI is potentially capable of achieving 10 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. © 2012 SPIE. -6
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SPACE TELESCOPES AND INSTRUMENTATION 2012: OPTICAL, INFRARED, AND MILLIMETER WAVE 8442 2012年We have been developing an immersion grating for high-resolution spectroscopy in the mid-infrared (MIR) wavelength region. A MIR (12-18 mu m) high-resolution (R = 20,000-30,000) spectrograph with the immersion grating is proposed for SPICA, Japanese next-generation space telescope. The instrument will be the world's first high-resolution spectrograph in space, and it would make great impacts on infrared astronomy. To realize a high-efficiency immersion grating, optical properties and machinability of bulk materials are the critical issues. There are three candidate materials with good MIR transmittance; CdTe (n = 2.65), CdZnTe (n = 2.65), and KRS5 (n = 2.30). From measurements of transmittance with FTIR and of homogeneity with phase-shifting interferometry at 1.55 mu m, we confirmed that CdZnTe is the best material that satisfies all the optical requirements. As for machinability, by appling Canon's diamond cutting (planing) technique, fine grooves that meet our requirement were successfully cut on flats for all the materials. We also managed to fabricate a small CdZnTe immersion grating, which shows a high grating efficiency from the air. For the reflective metal coating, we tried Au (with thin underlying layer of Cr) and Al on CdZnTe flats both by sputter deposition and vapor deposition. All samples are found to be robust under 77 K and some of them achieve required reflectivity. Despite several remaining technical issues, the fabrication of CdZnTe immersion grating appears to be sound.
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SPACE TELESCOPES AND INSTRUMENTATION 2012: OPTICAL, INFRARED, AND MILLIMETER WAVE 8442 2012年This paper presents a conceptual design for a spectrometer designed specifically for characterizing transiting exoplanets with space-borne infrared telescopes. The design adopting cross-dispersion is intended to be simple, compact, highly stable, and has capability of simultaneous coverage over a wide wavelength region with high throughput. Typical wavelength coverage and spectral resolving power is 1-13 mu m with a spectral resolving power of similar to a few hundred, respectively. The baseline design consists of two detectors, two prisms with a dichroic coating and microstructured grating surfaces, and three mirrors. Moving parts are not adopted. The effect of defocusing is evaluated for the case of a simple shift of the detector, and anisotropic defocusing to maintain the spectral resolving power. Variations in the design and its application to planned missions are also discussed.
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SPACE TELESCOPES AND INSTRUMENTATION 2012: OPTICAL, INFRARED, AND MILLIMETER WAVE 8442 2012年We present the Prototype-testbed for Infrared Optics and Coronagraphs (PINOCO) which is a large, multi-purpose cryogenic chamber. At present, the priority for PINOCO is to evaluate binary pupil mask coronagraphs in the mid-infrared wavelength region, which are planned to be adopted for the SPICA coronagraph instrument. In addition, various other experiments are possible using PINOCO: testing diverse high dynamic-range techniques, mirrors, active optics, infrared detectors, filters and spectral dispersion devices, the mechanics of the instruments, measurement of material properties, and so on. PINOCO provides a work space of 1m x 1m x 0.3m, of which inside is cooled to <5K. Flexible access to the work surface is possible by removing detachable plates at the four sides and on the top of the chamber. At the interface to the exterior, PINOCO is currently equipped with an optical window, electric connectors, and an interferometer stage. PINOCO is cooled by two GM-cycle cryo-coolers, so no cryogen is needed. A cooling test of PINOCO was successfully completed.
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Publications of the Astronomical Society of Japan 63(4) 873-879 2011年8月25日We conducted a number of multi-color/broadband coronagraph experiments using a vacuum chamber and a binary-shaped pupil mask, which in principle should work at all wavelengths, in the context of the research and development of a stellar coronagraph to observe extra-solar planets (exoplanets) directly. The aim of this work is to demonstrate that subtraction of the Point Spread Function (PSF) and multi-color/broadband experiments using a binary-shaped pupil mask coronagraph would help to improve the contrast in observations of exoplanets. A checkerboard mask, a kind of binary-shaped pupil mask, was used. We improved the temperature stability by installing the coronagraph optics in a vacuum chamber, while controlling the temperature of the optical bench, and covering the vacuum chamber with thermal insulation layers. Active wavefront control was not applied in this work. We evaluated how much the PSF subtraction contributed to the high-contrast observation by subtracting images obtained through the coronagraph. We also carried out multi-color/broadband experiments in order to demonstrate a more realistic observation using Super luminescent Light Emitting Diodes (SLEDs) with center wavelengths of 650 nm, 750 nm, 800 nm, and 850 nm. A contrast of 2.3 × 10 was obtained for the raw coronagraphic image and a contrast of 1.3 × 10 was achieved after PSF subtraction with a He-Ne laser at 632.8 nm wavelength. Thus, the contrast was improved by around two orders of magnitude from the raw contrast by subtracting the PSF. We achieved contrasts of 3.1 × 10 , 1.1 × 10 , 1.6 × 10 , and 2.5 × 10 at the bands of 650 nm, 750 nm, 800 nm, and 850 nm, respectively, in multi-color/broadband experiments. The results show that the contrast within each of the wavelength bands was significantly improved compared with the non-coronagraphic optics. We demonstrated that PSF subtraction is potentially beneficial for improving the contrast of a binary-shaped pupil mask coronagraph; this coronagraph produces a significant improvement in contrast with multi-color/broadband light sources. © 2011. Astronomical Society of Japan. -7 -9 -7 -6 -6 -6
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 63(4) 873-879 2011年8月We conducted a number of multi-color/broadband coronagraph experiments using a vacuum chamber and a binary-shaped pupil mask, which in principle should work at all wavelengths, in the context of the research and development of a stellar coronagraph to observe extra-solar planets (exoplanets) directly. The aim of this work is to demonstrate that subtraction of the Point Spread Function (PSF) and multi-color/broadband experiments using a binary-shaped pupil mask coronagraph would help to improve the contrast in observations of exoplanets. A checkerboard mask, a kind of binary-shaped pupil mask, was used. We improved the temperature stability by installing the coronagraph optics in a vacuum chamber, while controlling the temperature of the optical bench, and covering the vacuum chamber with thermal insulation layers. Active wavefront control was not applied in this work. We evaluated how much the PSF subtraction contributed to the high-contrast observation by subtracting images obtained through the coronagraph. We also carried out multi-color/broadband experiments in order to demonstrate a more realistic observation using Super luminescent Light Emitting Diodes (SLEDs) with center wavelengths of 650 nm, 750 nm, 800 nm, and 850 nm. A contrast of 2.3 x 10(-7) was obtained for the raw coronagraphic image and a contrast of 1.3 x 10(-9) was achieved after PSF subtraction with a He-Ne laser at 632.8 nm wavelength. Thus, the contrast was improved by around two orders of magnitude from the raw contrast by subtracting the PSF. We achieved contrasts of 3.1 x 10(-7), 1.1 x 10(-6), 1.6 x 10(-6), and 2.5 x 10(-6) at the bands of 650 nm, 750 nm, 800 urn, and 850 nm, respectively, in multi-color/broadband experiments. The results show that the contrast within each of the wavelength bands was significantly improved compared with the non-coronagraphic optics. We demonstrated that PSF subtraction is potentially beneficial for improving the contrast of a binary-shaped pupil mask coronagraph; this coronagraph produces a significant improvement in contrast with multi-color/broadband light sources.
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ADVANCES IN SPACE RESEARCH 47(9) 1455-1462 2011年5月The SPICA coronagraph instrument (SCI) provides high-contrast imaging and moderate resolution (R<200) spectroscopy at the wavelength range from 3.5 to 27 mu m. Based on the planet evolutional model calculated by Burrows et al. (2003), SCI will search for gas giant planets down to one Jupiter mass around nearby young (1 Gyr) stars and two Jupiter masses around nearby old (5 Gyr) stars. SCI also allows to characterizing those planets of less than I Gyr by spectroscopic observations to reveal the nature of planetary formation and evolution.Focusing on the high sensitivity and high contrast at wavelengths longer than 10 pm, we show that SCI also allows us to directly image icy giant planets like Uranus and Neptune as well as gas giant planets around nearby early-type stars. In this paper, we compare the capabilities of SCI and the JWST coronagraphs and also discuss a new approach to answering questions concerning the formation and evolution of planetary systems through planet detection with SCI. (C) 2011 COSPAR. Published by Elsevier Ltd. All rights reserved.
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APPLIED OPTICS 49(20) 3941-3948 2010年7月 査読有りWe tested the optical performance at cryogenic temperatures of an 800 mm diameter lightweight mirror, consisting of carbon-fiber reinforced silicon carbide and with a mass of 11.2 kg. The ceramic composite of the mirror was HB-Cesic, developed by ECM, Germany, and Mitsubishi Electric Corporation, Japan. The test was carried out while the mirror was mounted, via Invar stress relief supports, on a lightweight optical bench also made of HB-Cesic. During the test, both the mirror and the optical bench were cooled to 18 K in a liquid-helium chamber. The test consisted of measuring the mirror's change of surface figure with an interferometer installed outside the cryo-chamber. The cryogenic deformation of the mirror was 110 nm RMS with no significant residual deformation after cooling, which is very promising for the applicability of the HB-Cesic composite to large lightweight cryogenic space optics. (C) 2010 Optical Society of America
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Applied optics 49(20) 3941-3948 2010年7月 査読有り
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ADVANCES IN SPACE RESEARCH 45(8) 1000-1006 2010年4月The SPace Infrared telescope for Cosmology and Astrophysics (SPICA) is a proposed mid-to-far infrared (4-200 mu m) astronomy misson, scheduled for launch in 2017. A single. 3.5 m aperture telescope would provide superior image quality at 5-200 mu m, and its very cold (similar to 5 K) instrumentation would provide superior sensitivity in the 25-200 mu m wavelength regimes. This would provide a breakthrough opportunity for studies of exoplanets, protoplanetary and debris disk, and small solar system bodies This paper summarizes the potential scientific Impacts for the proposed instrumentation (C) 2009 COSPAR Published by Elsevier Ltd All rights reserved
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PATHWAYS TOWARDS HABITABLE PLANETS 430 284-+ 2010年We present the SPICA Coronagraph Instrument for the direct imaging and spectroscopy of exoplanets. The SPICA mission gives us a unique opportunity for high-contrast observations because of the large telescope aperture, the simple pupil shape, and the capability for infrared observations from space. The primary goal of this coronagraph is the direct detection and spectroscopy of Jovian exoplanets. The specifications, performance, and the design of the instrument are shown. The main wavelengths and the contrast required for the observations are 3.5 - 27 mu m, and 10(-6), respectively. We also show the progress of the development of key technology to realize this instrument. The non-coronagraphic mode of this instrument is potentially useful for characterization of inner planets via observation of planetary transit and Color Differential Astrometry(CDA). We expect the SPICA coronagraph will provide drastic progress for understanding various planetary systems by it's unique capability, mid will be a fruitful precursor for a future mission targeting terrestrial planets.
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Proceedings of SPIE - The International Society for Optical Engineering 7731 2010年SPICA (Space Infrared Telescope for Cosmology and Astrophysics) is a Japan-led infrared astronomical satellite project with a 3-m-class telescope in collaboration with Europe. The telescope is cooled down to temperature below 6 K in space by a combination of mechanical coolers with radiative cooling in space. The telescope has requirements for its total weight to be lighter than 700 kg and for the imaging performance to be diffraction-limited at 5 μm at 6 K. The mirrors will be made of silicon carbide (SiC) or its related material, which has large heritages of the AKARI and Herschel telescopes. The design of the telescope system has been studied by the Europe-Japan telescope working group led by ESA with European industries to meet the requirements. As for optical testing, responsibilities will be split between Europe and Japan so that final optical verification at temperatures below 10 K will be executed in Japan. We present our recent optical testing activities in Japan for the SPICA telescope, which include the numerical and experimental studies of stitching interferometry as well as modifications of the 6-m-diameter radiometer space chamber facility at Tsukuba Space Center in JAXA. We also show results of cryogenic optical testing of the 160-mm and 800-mm lightweight mirrors made of a C/SiC material called HBCesic, which is a candidate mirror material for the SPICA telescope. © 2010 SPIE.
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SPACE TELESCOPES AND INSTRUMENTATION 2010: OPTICAL, INFRARED, AND MILLIMETER WAVE 7731 2010年SPICA (Space Infrared Telescope for Cosmology and Astrophysics) is a Japan-led infrared astronomical satellite project with a 3-m-class telescope in collaboration with Europe. The telescope is cooled down to temperature below 6 K in space by a combination of mechanical coolers with radiative cooling in space. The telescope has requirements for its total weight to be lighter than 700 kg and for the imaging performance to be diffraction-limited at 5 mu m at 6 K. The mirrors will be made of silicon carbide (SiC) or its related material, which has large heritages of the AKARI and Herschel telescopes. The design of the telescope system has been studied by the Europe-Japan telescope working group led by ESA with European industries to meet the requirements. As for optical testing, responsibilities will be split between Europe and Japan so that final optical verification at temperatures below 10 K will be executed in Japan. We present our recent optical testing activities in Japan for the SPICA telescope, which include the numerical and experimental studies of stitching interferometry as well as modifications of the 6-m-diameter radiometer space chamber facility at Tsukuba Space Center in JAXA. We also show results of cryogenic optical testing of the 160-mm and 800-mm lightweight mirrors made of a C/SiC material called HBCesic, which is a candidate mirror material for the SPICA telescope.
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SPACE TELESCOPES AND INSTRUMENTATION 2010: OPTICAL, INFRARED, AND MILLIMETER WAVE 7731 2010年We present the laboratory demonstration of a wavefront correction system for the SPICA project. We have been developing SPICA Coronagraph Instrument (SCI) for exoplanet detection and characterization. SCI employs a wavefront correction system with a 1024-element deformable mirror. The laboratory experiments demonstrated that 10(6) dynamic ranges at 3.5 lambda/D can be achieved after speckle nulling by using a DM at the He-Ne laser wavelength. We also started a wide-band wavefront correction experiment in the visible wavelengths. The combination of wide-band speckle nulling algorithm and a binary pupil mask will lead to a very wide-band, high contrast imaging system.
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SPACE TELESCOPES AND INSTRUMENTATION 2010: OPTICAL, INFRARED, AND MILLIMETER WAVE 7731 2010年The SPICA mission aims to achieve high spatial resolution and unprecedented sensitivity in the mid to far-infrared wavelength astronomy. We derived a set of pointing requirements from SPICA's mission requirements. Disturbance management over the SPICA system and an implementation of isolators are necessary, because cryogenic coolers' disturbances could generate vibration. Alignment and random pointing errors for focal-plane instruments are reduced with a focal-plane guidance camera. Furthermore, an additional focal-plane camera and a tip-tilt mirror actuator are installed for coronagraph mode. This paper presents an overview of the SPICA pointing requirements and a feasibility study to achieve the requirements.
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PATHWAYS TOWARDS HABITABLE PLANETS 430 457-+ 2010年We present our results from a laboratory experiment on a binary-shaped pupil mask coronagraph in the context of instrumentation R&D for the direct observation of exo-planets. The aim of this work is testing an axiom of the coronagraph using the method employing the PSF (point spread function) subtraction in thermally-stable condition. Both the raw coronagraphic contrast and the contrast after the PSF subtraction are evaluated. A contrast of 2.6 x 10(-7) was achieved for the raw coronagraphic images by analyzing the areal mean of the observed dark regions. A contrast of 1.8 x 10(-9) was achieved for the PSF subtraction by the areal variance (1 sigma) of the observed dark regions. Application of the PSF subtraction to the coronagraph can ease the requirements for the raw contrast.
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ASTROPHYSICAL JOURNAL LETTERS 695(1) L88-L91 2009年4月Photometry of the A0 V main-sequence star HD 106797 with AKARI and Gemini/T-ReCS is used to detect excess emission over the expected stellar photospheric emission between 10 and 20 mu m, which is best attributed to hot circumstellar debris dust surrounding the star. The temperature of the debris dust is derived as T-d similar to 190 K by assuming that the excess emission is approximated by a single temperature blackbody. The derived temperature suggests that the inner radius of the debris disk is similar to 14 AU. The fractional luminosity of the debris disk is 1000 times brighter than that of our own zodiacal cloud. The existence of such a large amount of hot dust around HD 106797 cannot be accounted for by a simple model of the steady state evolution of a debris disk due to collisions, and it is likely that transient events play a significant role. Our data also show a narrow spectral feature between 11 and 12 mu m attributable to crystalline silicates, suggesting that dust heating has occurred during the formation and evolution of the debris disk of HD 106797.
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EXPERIMENTAL ASTRONOMY 23(1) 193-219 2009年3月The Space Infrared telescope for Cosmology and Astrophysics (SPICA) is planned to be the next space astronomy mission observing in the infrared. The mission is planned to be launched in 2017 and will feature a 3.5 m telescope cooled to < 5 K through the use of mechanical coolers. These coolers will also cool the focal plane instruments thus avoiding the use of consumables and giving the mission a long lifetime. SPICA's large, cold aperture will provide a two order of magnitude sensitivity advantage over current far infrared facilities (> 30 microns wavelength). We describe the scientific advances that will be made possible by this large increase in sensitivity and give details of the mission, spacecraft and focal plane conceptual design.
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Advances in Space Research 43(1) 181-186 2009年1月5日We present our first results from laboratory experiments on a binary-shaped checkerboard mask coronagraph that was fitted inside a vacuum chamber for the development of skills to the direct observation of extra-solar planets. The aim of this work was to utilize a vacuum chamber for our coronagraph experiments in order to achieve an environment with higher thermal stability and which is free from air turbulence. We also aimed to evaluate and improve the performance of such a system consisting of a vacuum chamber with a coronagraph set inside the chamber. Both the raw contrast and the contrast after point spread function (PSF) subtraction are evaluated. We sited the vacuum chamber in a clean room, and we installed an optical fiber coupled to a visible He-Ne laser, appropriate coronagraph optics, a temperature sensor and heaters in the chamber. This provided a vacuum environment and a temperature-controlled environment with a visible light source, and was shown to improve the stability of the coronagraph. A contrast of 1.7 × 10 was achieved for the raw coronagraphic images by analyzing the areal mean of all of the observed dark regions. A contrast of 7.3 × 10 was achieved for the PSF subtraction by areal variance (1σ) of all of the observed dark regions. Speckles were a major limiting factor throughout the dark regions of both the raw images and the PSF subtracted images. The application of PSF subtraction for the Space Infrared telescope for Cosmology and Astrophysics (SPICA) and for other platforms is discussed. © 2008 COSPAR. - 7 - 9
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SPICA JOINT EUROPEAN/JAPANESE WORKSHOP 2009年SPICA coronagraph will be operating from 3.5 to 27 micron and primarily aims at directly imaging extra-solar planets of nearby stars. A strong limitation of the coronagraph for the 3.5 m telescope is its angular resolution which allows planet detectability farther than a few AUs at best. Color Differential Astrometry (CDA) is a spectrophotometric method which would push the detection range to very close-in planets and up to a few AUs, thus nicely complementing the imaging coronagraph. We present the method and show how it can be implemented within the host coronagraph without major impacts on its optical setup. We give preliminary estimates of its sensitivity according to different extra-solar planetary systems configurations. Critical instrumental requirements are discussed, especially regarding detector gain stability.
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SPICA JOINT EUROPEAN/JAPANESE WORKSHOP 2009年We present the SPICA Coronagraph Instrument (SCI) for the direct imaging and spectroscopy of exo-planets. The SPICA mission gives us a unique opportunity for high-contrast observations because of the large telescope aperture, the simple pupil shape, and the capability for infrared observations from space. The primary target of SCI is Jovian exo-planets. Using the spectroscopy mode of SCI, we will try the detection and the characterization of mid-infrared line features of the atmosphere of exo-planets. The specifications, performance and the design of the instrument are shown. The main wavelengths and the contrast required for the observations are 3.5-27 mu m, and 10(-6), respectively. We also show the progress of the development of key technology to realize SCI. Laboratory demonstration of the principle of coronagraph, realistic design and fabrication of masks, and the development of cryogenic active optics have been carried out, or are successfully ongoing. We are preparing a cryogenic chamber for the tests of the whole infrared coronagraph. A potentially important by-product of the instrument, transit monitoring for characterization of exo-planets, is also described. We expect that SCI will provide drastic progress in the understanding of various planetary systems and will be a unique capability in the SPICA era.
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SPICA JOINT EUROPEAN/JAPANESE WORKSHOP 2009年SPICA will provide the best sensitivity and image quality than ever at 5-210 mu m. This will revolutionize our understanding of exoplanets, protoplanetary disks, debris disks, and Solar system small bodies. This paper summarizes such key sciences with SPICA discussed so far among the Japanese SPICA Science Working Group, stressing on the planetary formation, and exoplanet detection and characterization.
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Astrophysical Journal 695(1 PART 2) 2009年Photometry of the A0 V main-sequence star HD 106797 with AKARI and Gemini/T-ReCS is used to detect excess emission over the expected stellar photospheric emission between 10 and 20 μm, which is best attributed to hot circumstellar debris dust surrounding the star. The temperature of the debris dust is derived as T ∼ 190 K by assuming that the excess emission is approximated by a single temperature blackbody. The derived temperature suggests that the inner radius of the debris disk is ∼14 AU. The fractional luminosity of the debris disk is 1000 times brighter than that of our own zodiacal cloud. The existence of such a large amount of hot dust around HD 106797 cannot be accounted for by a simple model of the steady state evolution of a debris disk due to collisions, and it is likely that transient events play a significant role. Our data also show a narrow spectral feature between 11 and 12 μm attributable to crystalline silicates, suggesting that dust heating has occurred during the formation and evolution of the debris disk of HD 106797. © 2009. The American Astronomical Society. All rights reserved. d
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EXOPLANETS AND DISKS: THEIR FORMATION AND DIVERSITY 1158 89-+ 2009年As a result of IRAS observations, main-sequence stars that have circumstellar debris disks and thus show infrared excess have been discovered. Since debris disks are thought to be the final stage of planet formation, it is very important to investigate the properties and evolution of debris disks statistically. Especially, mid-infrared observations become a key method for planet formation study because mid-infrared excess traces the thermal emission from debris dust in planet-forming regions. We are carrying on an unbiased survey of debris disk candidates that show mid-infrared excess by using the AKARI/ARC mid-infrared all-sky survey data. So far, we have identified seven new debris disk candidates that show large 18 gm excess. Here, we present the initial results of the debris disk survey.
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AKARI, A LIGHT TO ILLUMINATE THE MISTY UNIVERSE 418 109-+ 2009年Following the IRAS observations, many main-sequence stars that have circumstellar debris disks have been discovered through their infrared excesses. Since debris disks are thought trace the final stages of planet formation, it is very important to statistically investigate the properties and evolution of debris disks. Observations at mid-infrared wavelengths are important for planet formation studies because mid-IR excesses trace the thermal emission from debris dust in their planet forming regions. We are carrying on an unbiased survey of debris disk candidates showing mid-infrared excesses by using the AKARI/IRC mid-infrared all-sky survey data. So far, we have identified 7 new debris disk candidates that show large 18 mu m excess. Here, we present the initial results of the debris disk survey.
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Cryogenics 48(5-6) 189-197 2008年5月The AKARI satellite (formerly known as ASTRO-F) is Japan's first infrared astronomical satellite. AKARI is equipped with the infrared camera (IRC) and the far-infrared surveyor (FIS), which are cooled below 7 K. The AKARI's 68.5 cm telescope, which is made of SiC, is also cooled below 7 K. A unique feature of the AKARI cryostat is that it uses both cryogen and mechanical coolers. Using mechanical coolers, the helium lifetime can be greater than one year with 170 L of liquid helium. AKARI was launched on February 21, 2006 (UT), from the Uchinoura Space Center (USC). It has been performing successfully in orbit. © 2008 Elsevier Ltd. All rights reserved.
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