9,267 research outputs found
When holography meets coherent diffraction imaging
Modern imaging techniques at the molecular scale rely on utilizing novel
coherent light sources like X-ray free electron lasers for the ultimate goal of
visualizing such objects as individual biomolecules rather than crystals. Here,
unlike in the case of crystals where structures can be solved by model building
and phase refinement, the phase distribution of the wave scattered by an
individual molecule must directly be recovered. There are two well-known
solutions to the phase problem: holography and coherent diffraction imaging
(CDI). Both techniques have their pros and cons. In holography, the
reconstruction of the scattered complex-valued object wave is directly provided
by a well-defined reference wave that must cover the entire detector area which
often is an experimental challenge. CDI provides the highest possible, only
wavelength limited, resolution, but the phase recovery is an iterative process
which requires some pre-defined information about the object and whose outcome
is not always uniquely-defined. Moreover, the diffraction patterns must be
recorded under oversampling conditions, a pre-requisite to be able to solve the
phase problem. Here, we report how holography and CDI can be merged into one
superior technique: holographic coherent diffraction imaging (HCDI). An inline
hologram can be recorded by employing a modified CDI experimental scheme. We
demonstrate that the amplitude of the Fourier transform of an inline hologram
is related to the complex-valued visibility, thus providing information on
both, the amplitude and the phase of the scattered wave in the plane of the
diffraction pattern. With the phase information available, the condition of
oversampling the diffraction patterns can be relaxed, and the phase problem can
be solved in a fast and unambiguous manner.Comment: 22 pages, 7 figure
Phase Retrieval with Application to Optical Imaging
This review article provides a contemporary overview of phase retrieval in
optical imaging, linking the relevant optical physics to the information
processing methods and algorithms. Its purpose is to describe the current state
of the art in this area, identify challenges, and suggest vision and areas
where signal processing methods can have a large impact on optical imaging and
on the world of imaging at large, with applications in a variety of fields
ranging from biology and chemistry to physics and engineering
Recommended from our members
ToScA North America (6 – 8 June 2017, The University of Texas, Austin, TX) Program
ToScA North America will address key areas of science,
including Multi-modal Imaging, Geosciences, Forensics, Increasing Contrast,
Educational Outreach, Data, Materials Science and Medical and Biological
Science.University of Texas High-Resolution X-ray CT Facility (UTCT);
Jackson School of Geosciences, The University of Texas at Austin;
Natural History Museum (London);
Royal Microscopical Society (Oxford, UK)Geological Science
Harmonically matched grating-based full-field quantitative high-resolution phase microscope for observing dynamics of transparent biological samples
We have developed a full-field high resolution quantitative phase imaging technique for observing dynamics of transparent biological samples. By using a harmonically matched diffraction grating pair (600 and 1200
lines/mm), we were able to obtain non-trivial phase difference (other than 0° or 180°) between the output ports of the gratings. Improving upon our previous design, our current system mitigates astigmatism artifacts and is
capable of high resolution imaging. This system also employs an improved phase extraction algorithm. The system has a lateral resolution of 1.6 ÎĽm and a phase sensitivity of 62 mrad. We employed the system to acquire high resolution phase images of onion skin cells and a phase movie of amoeba
proteus in motion
Maskless imaging of dense samples using pixel super-resolution based multi-height lensfree on-chip microscopy.
Lensfree in-line holographic microscopy offers sub-micron resolution over a large field-of-view (e.g., ~24 mm2) with a cost-effective and compact design suitable for field use. However, it is limited to relatively low-density samples. To mitigate this limitation, we demonstrate an on-chip imaging approach based on pixel super-resolution and phase recovery, which iterates among multiple lensfree intensity measurements, each having a slightly different sample-to-sensor distance. By digitally aligning and registering these lensfree intensity measurements, phase and amplitude images of dense and connected specimens can be iteratively reconstructed over a large field-of-view of ~24 mm2 without the use of any spatial masks. We demonstrate the success of this multi-height in-line holographic approach by imaging dense Papanicolaou smears (i.e., Pap smears) and blood samples
Modern optical astronomy: technology and impact of interferometry
The present `state of the art' and the path to future progress in high
spatial resolution imaging interferometry is reviewed. The review begins with a
treatment of the fundamentals of stellar optical interferometry, the origin,
properties, optical effects of turbulence in the Earth's atmosphere, the
passive methods that are applied on a single telescope to overcome atmospheric
image degradation such as speckle interferometry, and various other techniques.
These topics include differential speckle interferometry, speckle spectroscopy
and polarimetry, phase diversity, wavefront shearing interferometry,
phase-closure methods, dark speckle imaging, as well as the limitations imposed
by the detectors on the performance of speckle imaging. A brief account is
given of the technological innovation of adaptive-optics (AO) to compensate
such atmospheric effects on the image in real time. A major advancement
involves the transition from single-aperture to the dilute-aperture
interferometry using multiple telescopes. Therefore, the review deals with
recent developments involving ground-based, and space-based optical arrays.
Emphasis is placed on the problems specific to delay-lines, beam recombination,
polarization, dispersion, fringe-tracking, bootstrapping, coherencing and
cophasing, and recovery of the visibility functions. The role of AO in
enhancing visibilities is also discussed. The applications of interferometry,
such as imaging, astrometry, and nulling are described. The mathematical
intricacies of the various `post-detection' image-processing techniques are
examined critically. The review concludes with a discussion of the
astrophysical importance and the perspectives of interferometry.Comment: 65 pages LaTeX file including 23 figures. Reviews of Modern Physics,
2002, to appear in April issu
Spatial image modulation to improve performance of computed tomography imaging spectrometer
Computed tomography imaging spectrometers ("CTIS"s) having patterns for imposing spatial structure are provided. The pattern may be imposed either directly on the object scene being imaged or at the field stop aperture. The use of the pattern improves the accuracy of the captured spatial and spectral information
Imaging Protein Fibers at the Nanoscale and In Situ.
Protein self-assembly offers a rich repertoire of tools and technologies. However, despite significant progress in this area, a deterministic measure of the phenomenon, which might lead to predictable relationships between protein components, assembly mechanisms, and ultimately function, is lacking. Often the challenge relates to the choice of the most informative and precise measurements that can link the chemistry of the building blocks with the resulting assembly, ideally in situ and in real time. Using the example of protein fibrillogenesis-a self-assembly process fundamental to nearly every aspect of biological organization, from viral assembly to tissue restoration-this chapter demonstrates how protein self-assembly can be visually and precisely measured while providing measurement protocols applicable to other self-assembly systems
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