7,930 research outputs found
Large Scale 3D Image Reconstruction in Optical Interferometry
Astronomical optical interferometers (OI) sample the Fourier transform of the
intensity distribution of a source at the observation wavelength. Because of
rapid atmospheric perturbations, the phases of the complex Fourier samples
(visibilities) cannot be directly exploited , and instead linear relationships
between the phases are used (phase closures and differential phases).
Consequently, specific image reconstruction methods have been devised in the
last few decades. Modern polychromatic OI instruments are now paving the way to
multiwavelength imaging. This paper presents the derivation of a
spatio-spectral ("3D") image reconstruction algorithm called PAINTER
(Polychromatic opticAl INTErferometric Reconstruction software). The algorithm
is able to solve large scale problems. It relies on an iterative process, which
alternates estimation of polychromatic images and of complex visibilities. The
complex visibilities are not only estimated from squared moduli and closure
phases, but also from differential phases, which help to better constrain the
polychromatic reconstruction. Simulations on synthetic data illustrate the
efficiency of the algorithm.Comment: EUSIPCO, Aug 2015, NICE, Franc
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Coherent microscopy and optical coherence tomography for biomedical applications
This paper was presented at the 3rd Micro and Nano Flows Conference (MNF2011), which was held at the Makedonia Palace Hotel, Thessaloniki in Greece. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, Aristotle University of Thessaloniki, University of Thessaly, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute.In recent years many new methods of 3D optical imaging have been introduced that are applicable to the study of micro- and nano-scale flows. Coherent microscopy and optical coherence tomography join more established methods such as coherence scanning interferometry and confocal microscopy. These methods are very closely related and, using linear systems theory, can be compared in terms of their point spread and transfer functions. This paper introduces linear theory, demonstrates the main differences between the methods and discusses their use in micro- and nano-scale flow measurement. It is shown that coherent microscopy is currently the only method capable of single shot recording and consequently simultaneous whole-field flow measurement. Its use is limited to sparsely seeded flows however, such that individual particles can be identified. The other techniques provide increased 3D discrimination. Using a large numerical aperture, confocal microscopy and coherence scanning interferometry provide the most detailed 3D images making use the additional information available when the object is illuminated with plane waves propagating at different angles. In contrast optical coherence tomography uses the information that is available when the object is illuminated with different wavelengths. It is shown that the fundamental difference between these approaches is that the lateral and axial resolutions are decoupled in OCT making the technique easily scalable. This and the development of modern tunable laser sources, make OCT the method of choice for many biomedical applications
The 2010 Interferometric Imaging Beauty Contest
We present the results of the fourth Optical/IR Interferometry Imaging Beauty
Contest. The contest consists of blind imaging of test data sets derived from
model sources and distributed in the OI-FITS format. The test data consists of
spectral data sets on an object "observed" in the infrared with spectral
resolution. There were 4 different algorithms competing this time: BSMEM the
Bispectrum Maximum Entropy Method by Young, Baron & Buscher; RPR the Recursive
Phase Reconstruction by Rengaswamy; SQUEEZE a Markov Chain Monte Carlo
algorithm by Baron, Monnier & Kloppenborg; and, WISARD the Weak-phase
Interferometric Sample Alternating Reconstruction Device by Vannier & Mugnier.
The contest model image, the data delivered to the contestants and the rules
are described as well as the results of the image reconstruction obtained by
each method. These results are discussed as well as the strengths and
limitations of each algorithm.Comment: To be published in SPIE 2010 "Optical and infrared interferometry II
Stellar intensity interferometry: Optimizing air Cherenkov telescope array layouts
Kilometric-scale optical imagers seem feasible to realize by intensity
interferometry, using telescopes primarily erected for measuring Cherenkov
light induced by gamma rays. Planned arrays envision 50--100 telescopes,
distributed over some 1--4 km. Although array layouts and telescope sizes
will primarily be chosen for gamma-ray observations, also their interferometric
performance may be optimized. Observations of stellar objects were numerically
simulated for different array geometries, yielding signal-to-noise ratios for
different Fourier components of the source images in the interferometric
-plane. Simulations were made for layouts actually proposed for future
Cherenkov telescope arrays, and for subsets with only a fraction of the
telescopes. All large arrays provide dense sampling of the -plane due to
the sheer number of telescopes, irrespective of their geographic orientation or
stellar coordinates. However, for improved coverage of the -plane and a
wider variety of baselines (enabling better image reconstruction), an exact
east-west grid should be avoided for the numerous smaller telescopes, and
repetitive geometric patterns avoided for the few large ones. Sparse arrays
become severely limited by a lack of short baselines, and to cover
astrophysically relevant dimensions between 0.1--3 milliarcseconds in visible
wavelengths, baselines between pairs of telescopes should cover the whole
interval 30--2000 m.Comment: 12 pages, 10 figures; presented at the SPIE conference "Optical and
Infrared Interferometry II", San Diego, CA, USA (June 2010
Why Chromatic Imaging Matters
During the last two decades, the first generation of beam combiners at the
Very Large Telescope Interferometer has proved the importance of optical
interferometry for high-angular resolution astrophysical studies in the near-
and mid-infrared. With the advent of 4-beam combiners at the VLTI, the u-v
coverage per pointing increases significantly, providing an opportunity to use
reconstructed images as powerful scientific tools. Therefore, interferometric
imaging is already a key feature of the new generation of VLTI instruments, as
well as for other interferometric facilities like CHARA and JWST. It is thus
imperative to account for the current image reconstruction capabilities and
their expected evolutions in the coming years. Here, we present a general
overview of the current situation of optical interferometric image
reconstruction with a focus on new wavelength-dependent information,
highlighting its main advantages and limitations. As an Appendix we include
several cookbooks describing the usage and installation of several state-of-the
art image reconstruction packages. To illustrate the current capabilities of
the software available to the community, we recovered chromatic images, from
simulated MATISSE data, using the MCMC software SQUEEZE. With these images, we
aim at showing the importance of selecting good regularization functions and
their impact on the reconstruction.Comment: Accepted for publication in Experimental Astronomy as part of the
topical collection: Future of Optical-infrared Interferometry in Europ
High-speed in vitro intensity diffraction tomography
We demonstrate a label-free, scan-free intensity diffraction tomography technique utilizing annular illumination (aIDT) to rapidly characterize large-volume three-dimensional (3-D) refractive index distributions in vitro. By optimally matching the illumination geometry to the microscope pupil, our technique reduces the data requirement by 60 times to achieve high-speed 10-Hz volume rates. Using eight intensity images, we recover volumes of ∼350 μm × 100 μm × 20 μm, with near diffraction-limited lateral resolution of ∼ 487 nm and axial resolution of ∼ 3.4 μm. The attained large volume rate and high-resolution enable 3-D quantitative phase imaging of complex living biological samples across multiple length scales. We demonstrate aIDT’s capabilities on unicellular diatom microalgae, epithelial buccal cell clusters with native bacteria, and live Caenorhabditis elegans specimens. Within these samples, we recover macroscale cellular structures, subcellular organelles, and dynamic micro-organism tissues with minimal motion artifacts. Quantifying such features has significant utility in oncology, immunology, and cellular pathophysiology, where these morphological features are evaluated for changes in the presence of disease, parasites, and new drug treatments. Finally, we simulate the aIDT system to highlight the accuracy and sensitivity of the proposed technique. aIDT shows promise as a powerful high-speed, label-free computational microscopy approach for applications where natural imaging is required to evaluate environmental effects on a sample in real time.https://arxiv.org/abs/1904.06004Accepted manuscrip
Review of the mathematical foundations of data fusion techniques in surface metrology
The recent proliferation of engineered surfaces, including freeform and structured surfaces, is challenging current metrology techniques. Measurement using multiple sensors has been proposed to achieve enhanced benefits, mainly in terms of spatial frequency bandwidth, which a single sensor cannot provide. When using data from different sensors, a process of data fusion is required and there is much active research in this area. In this paper, current data fusion methods and applications are reviewed, with a focus on the mathematical foundations of the subject. Common research questions in the fusion of surface metrology data are raised and potential fusion algorithms are discussed
Interferometry of Aurigae: Characterization of the asymmetric eclipsing disk
We report on a total of 106 nights of optical interferometric observations of
the Aurigae system taken during the last 14 years by four beam
combiners at three different interferometric facilities. This long sequence of
data provides an ideal assessment of the system prior to, during, and after the
recent 2009-2011 eclipse. We have reconstructed model-independent images from
the 10 in-eclipse epochs which show that a disk-like object is indeed
responsible for the eclipse. Using new 3D, time-dependent modeling software, we
derive the properties of the F-star (diameter, limb darkening), determine
previously unknown orbital elements (, ), and access the global
structures of the optically thick portion of the eclipsing disk using both
geometric models and approximations of astrophysically relevant density
distributions. These models may be useful in future hydrodynamical modeling of
the system. Lastly, we address several outstanding research questions including
mid-eclipse brightening, possible shrinking of the F-type primary, and any
warps or sub-features within the disk.Comment: 105 pages, 57 figures. This is an author-created, un-copyedited
version of an article accepted for publication in Astrophysical Journal
Supplement Series. IOP Publishing Ltd is not responsible for any errors or
omissions in this version of the manuscript or any version derived from i
Serial optical coherence microscopy for label-free volumetric histopathology
The observation of histopathology using optical microscope is an essential procedure for examination of tissue biopsies or surgically excised specimens in biological and clinical laboratories. However, slide-based microscopic pathology is not suitable for visualizing the large-scale tissue and native 3D organ structure due to its sampling limitation and shallow imaging depth. Here, we demonstrate serial optical coherence microscopy (SOCM) technique that offers label-free, high-throughput, and large-volume imaging of ex vivo mouse organs. A 3D histopathology of whole mouse brain and kidney including blood vessel structure is reconstructed by deep tissue optical imaging in serial sectioning techniques. Our results demonstrate that SOCM has unique advantages as it can visualize both native 3D structures and quantitative regional volume without introduction of any contrast agents
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