11,245 research outputs found
The Application of Preconditioned Alternating Direction Method of Multipliers in Depth from Focal Stack
Post capture refocusing effect in smartphone cameras is achievable by using
focal stacks. However, the accuracy of this effect is totally dependent on the
combination of the depth layers in the stack. The accuracy of the extended
depth of field effect in this application can be improved significantly by
computing an accurate depth map which has been an open issue for decades. To
tackle this issue, in this paper, a framework is proposed based on
Preconditioned Alternating Direction Method of Multipliers (PADMM) for depth
from the focal stack and synthetic defocus application. In addition to its
ability to provide high structural accuracy and occlusion handling, the
optimization function of the proposed method can, in fact, converge faster and
better than state of the art methods. The evaluation has been done on 21 sets
of focal stacks and the optimization function has been compared against 5 other
methods. Preliminary results indicate that the proposed method has a better
performance in terms of structural accuracy and optimization in comparison to
the current state of the art methods.Comment: 15 pages, 8 figure
Real-time optical manipulation of cardiac conduction in intact hearts
Optogenetics has provided new insights in cardiovascular research, leading to new methods for cardiac pacing, resynchronization therapy and cardioversion. Although these interventions have clearly demonstrated the feasibility of cardiac manipulation, current optical stimulation strategies do not take into account cardiac wave dynamics in real time. Here, we developed an allâoptical platform complemented by integrated, newly developed software to monitor and control electrical activity in intact mouse hearts. The system combined a wideâfield mesoscope with a digital projector for optogenetic activation. Cardiac functionality could be manipulated either in freeârun mode with submillisecond temporal resolution or in a closedâloop fashion: a tailored hardware and software platform allowed realâtime intervention capable of reacting within 2 ms. The methodology was applied to restore normal electrical activity after atrioventricular block, by triggering the ventricle in response to optically mapped atrial activity with appropriate timing. Realâtime intraventricular manipulation of the propagating electrical wavefront was also demonstrated, opening the prospect for realâtime resynchronization therapy and cardiac defibrillation. Furthermore, the closedâloop approach was applied to simulate a reâentrant circuit across the ventricle demonstrating the capability of our system to manipulate heart conduction with high versatility even in arrhythmogenic conditions. The development of this innovative optical methodology provides the first proofâofâconcept that a realâtime optically based stimulation can control cardiac rhythm in normal and abnormal conditions, promising a new approach for the investigation of the (patho)physiology of the heart
Spectral pre-modulation of training examples enhances the spatial resolution of the Phase Extraction Neural Network (PhENN)
The Phase Extraction Neural Network (PhENN) is a computational architecture,
based on deep machine learning, for lens-less quantitative phase retrieval from
raw intensity data. PhENN is a deep convolutional neural network trained
through examples consisting of pairs of true phase objects and their
corresponding intensity diffraction patterns; thereafter, given a test raw
intensity pattern PhENN is capable of reconstructing the original phase object
robustly, in many cases even for objects outside the database where the
training examples were drawn from. Here, we show that the spatial frequency
content of the training examples is an important factor limiting PhENN's
spatial frequency response. For example, if the training database is relatively
sparse in high spatial frequencies, as most natural scenes are, PhENN's ability
to resolve fine spatial features in test patterns will be correspondingly
limited. To combat this issue, we propose "flattening" the power spectral
density of the training examples before presenting them to PhENN. For phase
objects following the statistics of natural scenes, we demonstrate
experimentally that the spectral pre-modulation method enhances the spatial
resolution of PhENN by a factor of 2.Comment: 12 pages, 10 figure
Accelerated Modeling of Near and Far-Field Diffraction for Coronagraphic Optical Systems
Accurately predicting the performance of coronagraphs and tolerancing optical
surfaces for high-contrast imaging requires a detailed accounting of
diffraction effects. Unlike simple Fraunhofer diffraction modeling, near and
far-field diffraction effects, such as the Talbot effect, are captured by
plane-to-plane propagation using Fresnel and angular spectrum propagation. This
approach requires a sequence of computationally intensive Fourier transforms
and quadratic phase functions, which limit the design and aberration
sensitivity parameter space which can be explored at high-fidelity in the
course of coronagraph design. This study presents the results of optimizing the
multi-surface propagation module of the open source Physical Optics Propagation
in PYthon (POPPY) package. This optimization was performed by implementing and
benchmarking Fourier transforms and array operations on graphics processing
units, as well as optimizing multithreaded numerical calculations using the
NumExpr python library where appropriate, to speed the end-to-end simulation of
observatory and coronagraph optical systems. Using realistic systems, this
study demonstrates a greater than five-fold decrease in wall-clock runtime over
POPPY's previous implementation and describes opportunities for further
improvements in diffraction modeling performance.Comment: Presented at SPIE ASTI 2018, Austin Texas. 11 pages, 6 figure
Accurate position tracking of optically trapped live cells
Optical trapping is a powerful tool in Life Science research and is becoming common place in many microscopy laboratories and facilities. There is a growing need to directly trap the cells of interest rather than introduce beads to the sample that can affect the fundamental biological functions of the sample and impact on the very properties the user wishes to observe and measure. However, instabilities while tracking large inhomogeneous objects, such as cells, can make tracking position, calibrating trap strength and making reliable measurements challenging. These instabilities often manifest themselves as cell roll or re-orientation and can occur as a result of viscous drag forces and thermal convection, as well as spontaneously due to Brownian forces. In this paper we discuss and mathematically model the cause of this roll and present several experimental approaches for tackling these issues, including using a novel beam profile consisting of three closely spaced traps and tracking a trapped object by analysing fluorescence images. The approaches presented here trap T cells which form part of the adaptive immune response system, but in principle can be applied to a wide range of samples where the size and inhomogeneous nature of the trapped object can hinder particle tracking experiments
Roadmap on structured light
Structured light refers to the generation and application of custom light fields. As the tools and technology to create and detect structured light have evolved, steadily the applications have begun to emerge. This roadmap touches on the key fields within structured light from the perspective of experts in those areas, providing insight into the current state and the challenges their respective fields face. Collectively the roadmap outlines the venerable nature of structured light research and the exciting prospects for the future that are yet to be realized.Peer ReviewedPostprint (published version
Tight focusing of plane waves from micro-fabricated spherical mirrors
We derive a formula for the light field of a monochromatic plane wave that is
truncated and reflected by a spherical mirror. Our formula is valid even for
deep mirrors, where the aperture radius approaches the radius of curvature. We
apply this result to micro-fabricated mirrors whose size scales are in the
range of tens to hundreds of wavelengths, and show that sub-wavelength spot
sizes can be achieved. This opens up the possibility of scalable arrays of
tightly focused optical dipole traps without the need for high-performance
optical systems.Comment: 8 pages, 5 color figures, 1 .sty file; changes made in response to
referee comments; published in Optics Expres
Holographic optical trapping
Holographic optical tweezers use computer-generated holograms to create
arbitrary three-dimensional configurations of single-beam optical traps useful
for capturing, moving and transforming mesoscopic objects. Through a
combination of beam-splitting, mode forming, and adaptive wavefront correction,
holographic traps can exert precisely specified and characterized forces and
torques on objects ranging in size from a few nanometers to hundreds of
micrometers. With nanometer-scale spatial resolution and real-time
reconfigurability, holographic optical traps offer extraordinary access to the
microscopic world and already have found applications in fundamental research
and industrial applications.Comment: 8 pages, 7 figures, invited contribution to Applied Optics focus
issue on Digital Holograph
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