Direct detection of faint exoplanets is challenging due to a high-contrast ratio between a primary star and a planet. A high-contrast imaging system has an important role in directly detecting exoplanets. The system consists of coronagraph and speckle reduction technique. A common-path visible nulling coronagraph (VNC) is one of the attracting methods for high-contrast observation because of a simple optical configuration and achromatic stellar elimination. We introduced a spatial light modulator (SLM) into the common-path VNC to suppress residual speckles caused by wavefront aberrations. The SLM can potentially generate a huge dark hole thanks to its large pixel format. As a focal plane wavefront sensor, we utilized the self-coherent camera (SCC) method for the common-path VNC. We carried out the laboratory demonstration of the speckle reduction technique for the common-path VNC combined with the SCC methods. The experimental results show an initial contrast of 2.2 × 10-5 and a final contrast of 1.3 × 10-6 in monochromatic light at a wavelength of 633 nm. We discuss the limiting factors of the contrast for improvement of our demonstration to achieve the higher contrast.
We report experiments of solar ground-layer (GL) adaptive optics (AO) using the 60cm domeless solar telescope of the Hida Observatory, Japan. We developed an averaging-type GL wavefront sensor and confirmed that it properly worked in computer simulations. We set the wavefront sensor behind a conventional AO system and modified AO software so as to drive a deformable mirror using the GL sensor. We conducted solar observations with the GLAO system in September, 2017. It worked to improve observational images over wide fields.
An effective aperture with several tens or more kilometers is needed to resolve exoplanets. A hypertelescope consists of multiple elemental telescopes like an interferometric array. Light beams from the elemental telescopes are collected and densified and used to form a snap-shot image. Thus formed image, however, does not exhibit high quality features, because the spatial frequency sampling is not dense enough to image properly exoplanets. Some kind of image restoration should be implemented to reveal the surface features of exoplanets. We conduct the image restoration and show the results and the effectiveness of the image restoration through computer simulations.
An adaptive optics (AO) system is developed for the 60cm domeless solar telescope of the Hida Observatory, Japan. Its performances are analyzed by the computer simulations, and improved by replacing the Zernike polynomials by Karhunen-Loève functions. Also, a tomographic wavefront sensor is developed for a ground-layer AO system. From test data acquired at the Hida observatory, wavefront-phase maps both in the ground-layer and in an upper layer are successfully derived.
We designed and fabricated an achromatic eight-octant phase mask (8OPM) for broadband coronagraphic observations of exoplanets. The fabricated 8OPM is composed of three-layer eight-octant half-wave plates based on photonic crystals. By using Jones calculus, it is shown that the three-layer 8OPM achieves much higher contrast over broad wavelength range than that of the previous single-layer design. We carry out preliminary laboratory experiments of the coronagraph using the fabricated three-layer 8OPM. As a model star, we use several visible laser light sources for characterizing the coronagraphic performance. As a result, we obtain higher contrasts than theoretical ones of the single-layer 8OPM. However, the achieved contrasts are lower than the theoretical values of the three-layer one. At present we suspect that manufacturing errors of the half-wave plates in the 8OPM limit the achieved contrasts.
The Savart-Plate Lateral-shearing Interferometric Nuller for Exoplanets (SPLINE) is a kind of a visible nulling coronagraph for directly detecting exoplanets. The SPLINE consists of two crossed polarizers and a Savart plate placed between them. Theoretically the SPLINE realizes perfect cancellation of starlight. However, achievable contrast is limited by residual stellar speckles due to wavefront aberration caused by imperfect optical surfaces of the optical elements. For reducing the residual stellar speckles of the SPLINE, we propose a speckle nulling technique using a Liquid-Crystal Spatial Light Modulator (LCSLM) to create a dark hole. For the speckle nulling, we apply the Self-Coherent Camera (SCC) technique to the SPLINE for wavefront sensing in the focal plane. We report our recent progress on computer simulation and preliminary laboratory experiments of the speckle nulling technique applied to the SPLINE.
Phase-mask coronagraph holds the ability to detect exoplanets very close to their parent star. We report a new kind of phase mask that performs the contrast ratio of more than the tenth power of 10 for a circular aperture with shades of a secondary mirror and spiders. The phase distribution of the phase mask is numerically obtained by making the leaked light distribute outside the transparent part of the pupil. We applied the hybrid input-output algorithm, one of phase retrieval methods, to find the phase distribution of the phase mask. We show the characteristics of thus obtained phase mask.
We have been developing focal-plane phase-mask coronagraphs ultimately aiming at direct detection and characterization of Earth-like extrasolar planets by future space coronagraph missions. By utilizing photonic-crystal technology, we manufactured various coronagraphic phase masks such as eight-octant phase masks (8OPMs), 2nd-order vector vortex masks, and a 4th-order discrete (32-sector) vector vortex mask. Our laboratory experiments show that the 4th-order vortex mask reaches to higher contrast than the 2nd-order one at inner region on a focal plane. These results demonstrate that the higher-order vortex mask is tolerant of low-order phase aberrations such as tip-tilt errors. We also carried out laboratory demonstration of the 2nd-order vector vortex masks in the High-Contrast Imaging Testbed (HCIT) at the Jet Propulsion Laboratory (JPL), and obtained 10-8-level contrast owing to an adaptive optics system for creating dark holes. In addition, we manufactured a polarization-filtered 8OPM, which theoretically realizes achromatic performance. We tested the manufactured polarization-filtered 8OPM in the Infrared Coronagraphic Testbed (IRCT) at the JPL. Polychromatic light sources are used for evaluating the achromatic performance. The results suggest that 10-5- level peak-to-peak contrasts would be obtained over a wavelength range of 800-900 nm. For installing the focal-plane phase-mask coronagraph into a conventional centrally-obscured telescope with a secondary mirror, pupil-remapping plates have been manufactured for removing the central obscuration to enhance the coronagraphic performance. A result of preliminary laboratory demonstration of the pupil-remapping plates is also reported. In this paper, we present our recent activities of the photonic-crystal phase coronagraphic masks and related techniques for the high-contrast imaging.
We are developing a new adaptive optics (AO) system for the 60cm domeless solar telescope of the Hida Observatory, Japan. The system has a deformable mirror with 97 piezo-actuators, a Shack-Hartmann wavefront sensor with a 10×10-microlens array and standard personal computers. We conducted solar observations in September, 2013, and confirmed that our AO system cancelled image-shifts so that the deviations were within the resolution of the telescope. We report the detailed performances of our new AO system.
We have developed the Savart-Plate Lateral-shearing Interferometric Nuller for Exoplanets (SPLINE), which is a kind of
a nulling interferometer, for directly imaging exoplanets. The SPLINE consists of two polarizers and a Savart plate
between them. The SPLINE can theoretically obtain fully achromatic and stable nulled output. However, a drawback of
the SPLINE is its low system throughput due to the polarizers. For improving the system throughput, we propose a dualchannel
SPLINE using polarization beam splitters instead of the polarizers. We have carried out laboratory
demonstration of the dual-channel SPLINE. The achievable contrast of the SPLINE is limited by residual speckles
caused by surface roughness of optical elements. For improving the achievable contrast, we propose a method of
wavefront correction using a liquid-crystal spatial light modulator (LCSLM). We have carried out preliminary laboratory
demonstration using a liquid-crystal variable retarder (LCVR), instead of the LCSLM, for simulating the proposed
wavefront correction method. We report the laboratory demonstration in this paper.
One of the problems for direct observation of extrasolar planets is the speckle noise due to a wave-front error.
Therefore, high-accuracy adaptive optics is required for realizing a wavefront quality of λ/10000 rms. An unbalanced
nulling interferometer has a possibility to assist high-accuracy correction. In this paper, we propose the interferometer
with a four-quadrant phase mask in which an optical path is common. By using the mask, we succeed in stabilizing the
interference and taking measurements of wavefront errors with 10-times higher sensitivity. In this way, we expect to
construct high-accuracy adaptive optics which is more stable.
The Savart-Plate Lateral-shearing Interferometric Nuller for Exoplanet (SPLINE) is a stable and fully achromatic nulling
interferometer proposed for direct detection of extrasolar planets with segmented-mirror telescopes like the Thirty Meter
Telescope (TMT). The SPLINE uses a Savart plate, a kind of polarizing beam splitter, to split a light beam into two
orthogonally polarized ones with a lateral shift. The Savart plate placed between crossed polarizers causes fully
achromatic destructive interference for an on-axis star light. On the other hand, planetary light from an off-axis direction
does not destructively interfere due to the lateral shift. The SPLINE provides a stable interferometric output because of
its simple common-path optical design without an optical-path difference control system. We carried out laboratory
demonstrations of the SPLINE to evaluate its stability, achromaticity, and achievable contrast. As a result, a high
contrast of >104 (peak-to-peak contrast) is achieved using a broadband light source as a star model. In addition, we also
propose to apply a differential imaging technique to the SPLINE for improving achievable contrast. We report our recent
activities and show the results of the laboratory demonstrations.
Thirty Meter Telescope (TMT) will see the first light in 2019. We propose Second-Earth Imager for TMT (SEIT) as a
future instrument of TMT. The central science case of SEIT is direct imaging and characterization of habitable planets
around nearby late-type stars. Focusing on simultaneous spectroscopy of the central star and the planet, SEIT allows us
to remove an impact from the telluric absorption and then reveal the presence of oxygen molecules on the Earth-like
planets.
In order to achieve such a science goal, an extreme AO, a coronagraph, and a post-process technique for achieving high
contrast at the small inner working angle are key components. The combination of a shearing nulling interferometer and
a pupil remapping interferometer is applied to the first SEIT concept. The shearing nulling interferometer suppresses the
diffracted starlight after the extreme AO wavefront correction, and then the pupil remapping interferometer tackles the
speckle noise from starlight. Focusing on a fact that the pupil remapping interferometer has difficulty reconstructing the
wavefront from only the speckle noise, we found an unbalnced nulling technique enhances the performance of the pupil
remapping interferometer. We performed a numerical simulation to validate this concept and found this concept achieves
the 5-sigma detection contrast down to 8x10-8 at 10 mas for 5 hours. Thus, the SEIT concept detects habitable planets
with a radius two times that of the Earth around ten nearby M stars.
Photonic crystal, an artificial periodic nanostructure of refractive indices, is one of the attractive technologies for
coronagraph focal-plane masks aiming at direct imaging and characterization of terrestrial extrasolar planets. We
manufactured the eight-octant phase mask (8OPM) and the vector vortex coronagraph (VVC) mask very precisely using
the photonic crystal technology. Fully achromatic phase-mask coronagraphs can be realized by applying appropriate
polarization filters to the masks. We carried out laboratory experiments of the polarization-filtered 8OPM coronagraph
using the High-Contrast Imaging Testbed (HCIT), a state-of-the-art coronagraph simulator at the Jet Propulsion
Laboratory (JPL). We report the experimental results of 10-8-level contrast across several wavelengths over 10%
bandwidth around 800nm. In addition, we present future prospects and observational strategy for the photonic-crystal
mask coronagraphs combined with differential imaging techniques to reach higher contrast. We proposed to apply the
polarization-differential imaging (PDI) technique to the VVC, in which we built a two-channel coronagraph using
polarizing beam splitters to avoid a loss of intensity due to the polarization filters. We also proposed to apply the
angular-differential imaging (ADI) technique to the 8OPM coronagraph. The 8OPM/ADI mode mitigates an intensity
loss due to a phase transition of the mask and provides a full field of view around central stars. We present results of
preliminary laboratory demonstrations of the PDI and ADI observational modes with the phase-mask coronagraphs.
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.
Solar adaptive optics (AO) systems are developed at the 60cm domeless solar telescope in the Hida Observatory, Japan.
An AO system currently used has a deformable mirror with high-speed 97 electromagnetic actuators and a Shack-
Hartmann wavefront sensor with a 10x10-microlens array and 4000fps-CMOS camera. Its control frequency is about
1100-1400 Hz, and hence the -3dB cutoff frequency of the system is theoretically above 100 Hz. In parallel to
developing the system, a new full-scaled AO system is designed to be applicable to various observations, such as highdispersion
spectroscopy and simultaneous wide-range spectroscopy. The new system will work as classical AO at first.
The details of the current system, observational results using it, and the design of the new AO system are described.
The Vector Vortex Coronagraph (VVC) is one of the most attractive new-generation coronagraphs for ground- and
space-based exoplanet imaging/characterization instruments, as recently demonstrated on sky at Palomar and
in the laboratory at JPL, and Hokkaido University. Manufacturing technologies for devices covering wavelength
ranges from the optical to the mid-infrared, have been maturing quickly. We will review the current status of
technology developments supported by NASA in the USA (Jet Propulsion Laboratory-California Institute of
Technology, University of Arizona, JDSU and BEAMCo), Europe (University of Li`ege, Observatoire de Paris-
Meudon, University of Uppsala) and Japan (Hokkaido University, and Photonics Lattice Inc.), using liquid
crystal polymers, subwavelength gratings, and photonics crystals, respectively. We will then browse concrete
perspectives for the use of the VVC on upcoming ground-based facilities with or without (extreme) adaptive
optics, extremely large ground-based telescopes, and space-based internal coronagraphs.
We report laboratory demonstrations of an eight-octant phase-mask (EOPM) coronagraph for direct detection of
exoplanets. The EOPM coronagraph is a family of a four-quadrant phase-mask (FQPM) one, and shows better
coronagraphic performance for partially resolved stars. We manufactured an eight-octant ferroelectric liquid-crystal
(FLC) mask. The FLC mask is composed of eight-segmented half-wave plates whose principal axes are different
between adjacent segments. The mask operates as a fully achromatic EOPM when the FLC mask is placed between
crossed polarizers. We carried out laboratory experiments on the EOPM coronagraph by using partially resolved whitelight
source, and compared the performance with that of the FQPM one. As a result, we confirmed that the EOPM shows
higher contrast than the FQPM. A drawback of the proposed method is that the FLC mask can be used only for one
component of polarization of incoming light because it is necessary to use the polarizer in front of the FLC mask. To
solve this problem, a two-channel coronagraph, based on two polarizing beam splitters instead of the polarizers, is
proposed. Observational efficiency can significantly be improved because the two-channel coronagraph enables us to
detect both components of polarizations from exoplanets. We also report preliminary experimental results of laboratory
demonstrations of the two-channel coronagraph.
A solar adaptive optics system for a high-dispersion spectrograph is developed at the 60 cm domeless solar telescope of
the Hida Observatory in Japan. Details of its optical setup are described for implementing a scanning slit spectroscopy
with wavefront correction. A wavefront sensor used in the system is specified and a technique of reducing computational
cost in wavefront sensing is also described. In solar observations, the improvement of contrast in images obtained with
the adaptive optics system was demonstrated when a sunspot was used as a target of wavefront sensing.
An eight-octant phase-mask (EOPM) coronagraph is one of the highest performance coronagraphic concepts, and attains
simultaneously high throughput, small inner working angle, and large discovery space. However, its application to
ground-based telescopes such as the Subaru Telescope is challenging due to pupil geometry (thick spider vanes and large
central obstruction) and residual tip-tilt errors. We show that the Subaru Coronagraphic Extreme Adaptive Optics
(SCExAO) system, scheduled to be installed onto the Subaru Telescope, includes key technologies which can solve these
problems. SCExAO uses a spider removal plate which translates four parts of the pupil with tilted plane parallel plates.
The pupil central obstruction can be removed by a pupil remapping system similar to the PIAA optics already in the
SCExAO system, which could be redesigned with no amplitude apodization. The EOPM is inserted in the focal plane to
divide a stellar image into eight-octant regions, and introduces a π-phase difference between adjacent octants. This
causes a self-destructive interference inside the pupil area on a following reimaged pupil plane. By using a reflective
mask instead of a conventional opaque Lyot stop, the stellar light diffracted outside the pupil can be used for a
coronagraphic low-order wave-front sensor to accurately measure and correct tip-tilt errors. A modified inverse-PIAA
system, located behind the reimaged pupil plane, is used to remove off-axis aberrations and deliver a wide field of view.
We show that this EOPM coronagraph architecture enables high contrast imaging at small working angle on the Subaru
Telescope. Our approach could be generalized to other phase-mask type coronagraphs and other ground-based telescopes.
The building block method provides a promising algorithm to reconstruct an astronomical object image from its bispectrum. While the building block method has been well applied on stellar objects, in the present study we examine the applications to extended objects such as planets and satellites. We have obtained the visible light
specklegrams of Io (a Jupiter's satellite) at 515nm using the 2m telescope in Nishi-Harima Astronomical Observatory. We report a preliminary imaging result of Io using the building block method. The result is compared with the image as previously restored by the shift-and-add method with a deconvolution post-processing.
A solar adaptive optics system for the 60 cm domeless solar telescope of the Hida Observatory in Japan is developed. A
high-speed deformable mirror with 52 electromagnetic actuators is newly used in an experimental adaptive optics system.
The use of the mirror resulted in the improvement of Strehl ratios in laboratory experiments. In solar observations, the
system worked well when solar granulation was used as a target for wavefront sensing. An adaptive optics system being
developed for a vertical spectrograph of the domeless solar telescope is described.
A solar adaptive optics system is developed for the 60 cm domeless solar telescope of the Hida Observatory in Japan. It
is designed for compensating low order turbulence in G-band using a 52-electromagnetic-actuator deformable mirror, a
6x6 Shack-Hartmann wavefront sensor and standard personal computers. The details of the system, particularly features
of the deformable mirror are described. Laboratory experiments show that the use of adaptive optics raises the Strehl
ratio by a factor of five for turbulence of under 99Hz. In solar observations, the improvement of resolution in
long-exposure images with the adaptive optics system is demonstrated.
We present a method of the polarization degree analysis of exoplanets' objective-prism spectra. The polarization
analysis of the objective spectra can be used for discerning planet signal from noisy stellar light. The light reflected from
the planet is expected to be partially polarized, while the direct stellar light can be considered to be unpolarized. For
measuring objective spectra we use a four-quadrant polarization mask (FQPoM) coronagraph and a prism. The primary
suppression of starlight is achieved by destructive interference of the light passing through the central region of FQPoM.
For further suppression of starlight we use a polarization differential technique. By taking the difference between two
orthogonally polarized components of incoming light we can further suppress unpolarized starlight and reveal the
spectrum of the exoplanet. However, when the intensity contrast between the star and its planet is high, the starlight
noise impedes detection of the planetary spectrum. The analysis of the degree of polarization relieves the separation of
the planetary spectrum from the stellar noise. Moreover, any peculiar features in the objective spectra would be useful to
find out the location of the exoplanet. We obtained the experimental results under an intensity contrast of 3.5×10-5 and an
angular separation of 4.9 λ/D.
A four-quadrant phase-mask (FQPM) coronagraph can suppress perfectly stellar light when a star can be regarded as
a point-like source. However, the FQPM coronagraph is highly sensitive to partially resolved stars, and shows
second-order sensitivity to tip-tilt error leakage. Higher-order sensitivity is required for extremely high-contrast imaging
of nearby stars.
We propose an eight-octant phase-mask (EOPM) for achieving fourth-order sensitivity to tip-tilt errors. We
manufactured the phase-mask utilizing a nematic liquid crystal (LC) device, which is composed of eight segments. A
phase retardation of the LC can be adjustable by an applied voltage to the device. The LC phase-mask can be switched
between FQPM-mode and EOPM-mode by applying appropriate voltages to the segments. We carry out experiments on
the phase-mask coronagraph with various tip-tilt errors. The experimental results show the higher-order behavior of the
EOPM compared to the FQPM.
We present a current status of the laboratory experiments on the EOPM coronagraph, and also show coronagraphic
performance of the EOPM derived from numerical simulations.
The light from an exoplanet is expected to be different from that of its parent star in regard to polarization and spectral features. Thus, polarization or spectral differential technique will be a powerful tool for direct detection of exoplanets. We propose a novel technique that enables to detect both polarization and spectral differential images. This technique will be used in combination with the other high-contrast imagers to enhance the performance.
This approach uses two Wollaston prisms (WPs) and a thick retarder (TR) inserted between the WPs. Two WPs generate four images and make it possible to obtain polarization differential images. Spectra of these four images have sinusoidal patterns (channeled spectra) due to the WP-TR-WP system. By inserting an interference filter, this system works as bandpass filters whose center wavelengths are different between the images. Therefore, both polarization and spectral differential images can be obtained. Furthermore, we propose to use two variable retarders (VRs) to remove differential aberrations caused by different optical paths of these four images. One VR is inserted in front of WP-TR-WP system to modulate the polarized light beams, and the other one is inserted between WPs to modulate the channeled spectra. By modulating the retardations of the VRs, it becomes possible to remove the differential aberrations.
We present the principle of this method. Currently, we are conducting the preliminary laboratory experiment. The results of the laboratory demonstrations will be also reported.
This paper describes a PC-cluster-based observation system for improving the angular resolution of solar images. The system consists of two equipments separately working: one equipment realizes automatic acquisition of one hundred images at every fifteen seconds, and selects ten best images to be used in image processing. In the other one, image restoration and resolution improvement are carried out with a blind deconvolution method and a super-resolution method, respectively, using a PC cluster system. The system can take images at every fifteen seconds with high angular resolution. A test observation at the Hida Observatory confirmed a satisfactory performance of this system. The two equipments in the current hybrid system will be united in a future system that will realize image processing in pseudo-real time. A condition toward pseudo-real time processing is also investigated in this paper.
The light from exoplanets is expected to be partially polalized and the image intensity becomes different with the polarization direction. Based on this expectation we have reported the laboratory experiment of two-channel nulling stellar coronagraph for direct imaging of exoplanets, where a differential imaging with respect to mutually orthogonally polarized light is conducted. We show that this differential technique is also useful for obtaining objective spectra of exoplanets. Several experimental results on the differential objective spectrometer are reported.
A dual-channel nulling coronagraph to improve the detectability of
extrasolar planets is demonstrated. We have been developing a nulling
coronagraph with a four-quadrant polarization mask, and confirmed
its performance with monochromatic and polychromatic light sources.
However, the imperfections of the mask cause the leakage of the starlight, which is obstructive to the detection of faint companions. Here, we propose a two-channel nulling coronagraph, where s- and p-polarized components of the incident light are separated.
The light scattered and reflected from the atmosphere of an
extrasolar planet is expected to be partially polarized, while
the light from the parent star is usually unpolarized. Thus, the differential method, in which subtraction is taken between coronagraphic images of s- and p-polarized lights, is very useful for direct detection of extrasolar planets. In this approach, cancellation of the residual unpolarized starlight is realized when the coronagraphic performance of the two channels is identical.
We constructed the two-channel instrument. The experimental results confirm that the two-channel coronagraph can suppress the residual
stellar noise, and improve the detectability of faint companions.
The effects of the difference between two channels on the detectability are also discussed.
Nulling stellar coronagraph has been proposed to detect faint
objects very close to a bright point-like star, especially extra-solar planets. The principle of the nulling stellar coronagraph is to cause destructive interference for the light from a star. There have been proposed several methods for nulling interferometry. The key point of the nulling interferometry is the way to produce π-phase shift over wide range of wavelength. Here we propose a method for realizing achromatic π-phase shift utilizing polarization interference. The phase difference between two light beams that pass through different polarizers is π radians when these polarizers are placed between mutually orthogonal polarizer and analyzer. We adopt a ferroelectric liquid-crystal (FLC) device to convert the polarization direction of the incident beam. The FLC device is regarded as a birefringent device with retardation π, namely a half wave plate. The FLC device forms four-quadrant structure and is placed between the polarizer and the analyzer. By fixing the optic axes of the four-quadrant FLC suitably, it can rotate the incident linearly polarized light in parts by plus/minus 45°.
Geometric phase modulation is used to realize achromatic phase shift in nulling interferometer, where Fresnel rhombs are key components of the geometric phase modulator. Experimental results show high extinction ratio in visible region. Extension of our scheme to the infrared region is also discussed.
To avoid the drawbacks of conventional Fourier transform spectrometer (CFTS) based on the Michelson interferometer which needs a scanning system to acquire the interferogram in the temporal domain, the static Fourier transform (StFT) spectrometer has been developed. A new static Fourier-transform imaging spectrometer based on the Sagnac polariscope is proposed. The novelty of this work comes from slitless in this instrument, which means high throughput. The throughput advantage of this instrument over StFT imaging spectrometer based on Sagnac interferometer is presented. The principle and the system configuration are described. Several preliminary experimental results are shown.
A novel Fourier-transform imaging spectrometer based on Savart polariscope is presented. The novelty of this work comes from slitless in this instrument, which means high throughput. The effect on the interferogram due to the pixel size is analyzed. The principle and the system configuration are described. Several preliminary experimental results are shown.
Superresolution is attained for solar granulation images observed from the ground. The images are preprocessed with a blind deconvolution method, and then are superresolved. The resultant images show features with resolution higher than the diffraction limit.
The shift-and-add (SAA) method is applied to specklegrams of solar granulation to reconstruct its high-resolution image. The SAA recovers solar granulation from the atmospherically degraded images. From our reconstruction result it is shown that SAA method is useful for a largely extended object.
It is shown that high resolution imaging is possible by use of a reference star that is separated wider than the isoplanatic angle from an object under observation. A shift-and-add operation to the reference star results in a high resolution image of an object, though not diffraction-limited. Observational results of a binary star with angular separation of 22" indicate that a simple adaptive optics system is feasible in the visible region.
It is sometimes important to investigate the 3D structure of a small transparent
object, such as biological cells or optical fibers. Here we describe an interference
microscope with digital image processing systems, in which the interferograms of a small
phase-object projected in various directions are measured and then the internal structune of the object is digitally reconstructed by technique of computer tomography.
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