Adaptive optics (AO) is a powerful tool for correcting wavefront errors induced by complex structures of biological samples which significantly causes image degradation. A scene-based sensing technique is being popular in microscopic AO systems with Shack-Hartmann (SH) wavefront sensors. A problem in application of the technique is that the shapes of images observed on SAs vary dependently to their positions on the aperture, especially when using microscopic objectives with higher NAs. To mitigate this problem, a differential sensing technique is used that enables measuring image shifts with high correlations over the aperture. Experiments using an artificial testing target including fluorescent beads, which simulates the leaf of moss, were conducted to investigate imaging performances of the present AO system. Unbiased maximum ratios were measured from blurred and AO-corrected images, and then the Strehl ratios were derived from them. Resultant Strehl ratios were around 0.58.
Significance: A scene-based adaptive-optics (AO) system is developed and a method for investigating its imaging performance is proposed. The system enables derivation of Strehl ratios from observed images via collaboration with computer simulations. The resultant Strehl ratios are comparable with those of other current AO systems.
Aim: For versatile and noninvasive AO microscopy, a scene-based wavefront-sensing technique working on a Shack–Hartmann wavefront sensor is developed in a modal control system. The purpose of the research is to clarify the imaging performance of the AO system via the derivation of Strehl ratios from observed images toward applications in microscopy of living cells and tissues.
Approach: Two imaging metrics that can be directly measured from observed images (i.e., an energy concentration ratio and unbiased maximum ratio) are defined and related to the Strehl ratio via computer simulations. Experiments are conducted using artificial targets to measure the imaging metrics, which are then converted to Strehl ratios.
Results: The resultant Strehl ratios are >0.7 and 0.5 in the cases of defocus and higher aberrations, respectively. The half-widths at half-maximum of the AO-corrected bead images are favorably comparable to those of on-focus images under simple defocus aberration, and the AO system works both under bright-field illumination and on fluorescent bead images.
Conclusions: The proposed scene-based AO system is expected to work with a Strehl ratio of more than 0.5 when applied to high-resolution live imaging of cells and tissues under bright-field and fluorescence microscopies.
We develop a machine learning (ML) software to estimate morphological parameters (e.g., the half-light radius re) of high redshift galaxies in the Subaru/Hyper Suprime-Cam data. To make the ML software capture simultaneously galaxy morphological features and point spread function (PSF) broadening effects, we implement a two-stream convolutional neural network (CNN) for inputs of galaxy and PSF images. Thanks to large training samples of galaxy and PSF images, the two-stream CNN estimates re more accurately than a single-stream CNN with only galaxy images. Our ML software would be a useful tool to investigate galaxy morphological properties with PSF-unstable images obtained in future large-area ground-based surveys.
We have developed a microscopic adaptive optics (AO) system that corrects wavefront phase errors induced by complex structures of biological samples. The technique of correlation-based Shack-Hartmann (SH) sensing used in the AO system enables wavefront measurement using complex structures in a target as the reference. However, sub-images in the SH sensor become deformed dependently on the positions of sub-apertures as the NA of the microscopic objective is higher. This often deteriorates the accuracy of wavefront sensing. To mitigate the undesirable effect, we here propose a differential wavefront sensing technique with a mathematical formula, which is expected to measure wavefront at a better precision. Because differences in image shapes are less significant between nearby SAs, correlations between adjacent SAs are measured in the proposed method. We confirmed that the AO system worked as designed by experiments.
Adaptive optics (AO) is a promising technique for correcting wavefront errors induced by complex structures of biological samples which significantly causes image degradation. We develop a microscopic AO system with a Shack-Hartmann wavefront sensor based on image correlation. The correlation-based wavefront sensing is feasible using an extended object under bright-field illumination, as well as spot fluorescence. To make the correlation-based sensing more reliable, we newly introduce a technique of excluding sub-images with insufficient quality. We show experimental results under a variety of conditions for objects, light sources, and wavefront error sources. In any cases, we confirmed that the AO system effectively worked so as to improve image qualities.
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.
We aim at improving solar images partially compensated by Adaptive Optics (AO) or Ground-Layer (GL) AO using a phase diversity (PD) method. To reduce computational time in the PD execution, we develop a computer cluster system that enables restoration of several images in parallel. We set a PD-observational system downstream of an AO system in the Hida Observatory in Japan. Driving the AO system, we recorded focused and defocused solar images. They were segmented to partial images, and then were restored by the PD method. We show the results of solar image restoration, and also demonstrate the reduction of processing time by the computer cluster.
Live-cell imaging using fluorescent molecules is now essential for biological researches. However, images of living cells are accompanied with blur, which becomes stronger according to the depth inside the cells and tissues. This image blur is caused by the disturbance on light that goes through optically inhomogeneous living cells and tissues. Here, we show adaptive optics (AO) imaging of living plant cells. AO has been developed in astronomy to correct the disturbance on light caused by atmospheric turbulence. We developed AO microscope effective for the observation of living plant cells with strong disturbance by chloroplasts, and successfully obtained clear images inside plant cells.
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.
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 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 propose a new high contrast imager for Kyoto 4m segmented telescope called SEICA (Second-generation
Exoplanet Imager with Coronagraphic Adaptive optics), aiming at detection and characterization of selfluminous
gas giants within 10AU around nearby stars. SEICA is aggressively optimized for high performance
at very small inner working angle, 10-6 detection contrast at 0".1 in 1-hour integration. We start the on-sky
commissioning test in 2016 and the science observations in 2017. Since it is the first time to realize the highcontrast
imaging on the segmented telescope, SEICA is an important step toward future high contrast
sciences on Extremely Large Telescopes (ELTs). This paper presents an overall of the SEICA program and
the conceptual design for ultimate performance under given atmospheric conditions.
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.
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.
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.
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 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 apply some superresolution techniques to ultraviolet Betelgeuse images observed with the Hubble Space Telescope (HST). Betelgeuse images used here were observed from 1995 to 1999. The profile of Betelgeuse drastically changed during this period, and bright areas (hotspots) sometime appeared on its surface. Their sizes were comparable to the diffraction limit of the HST. Thus, to obtain information on Betelgeuse, the improvement of the resolution is necessary. Through applying superresolution methods to observed images, we clarify their utilities in the analysis of Betelgeuse images. We obtain the positional information on hotspots from superresolved images, and then carry out model fitting of Betelgeuse profiles. We describe the results of model fitting.
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.
We proposed a new method using likelihood evaluation for detecting astronomical faint moving objects (e.g. asteroids, Edgeworth-Kuiper belt objects). We applied our method to observed images, and showed its effectiveness in the detection of faint moving objects.
A blind deconvolution method is proposed for restoring a diffraction-limited object from a convolution image with a band-limited PSF. The method is based on conjugate-gradient minimization of an error metric defined in this paper. An image restored with the proposed method always satisfies nonnegativity constraint. The performance of the method is investigated by computer simulation.
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 the band-limit spectrum of a nonnegative image is represented as the auto-convolution of a spectrum whose cutoff is half of the band limit. The relation between the nonnegative image and its spectrum is used to construct a phase retrieval method and a superresolution method. Computer simulation results of these methods are shown.
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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