2,076 research outputs found
Quantitative imaging of the complexity in liquid bubbles' evolution reveals the dynamics of film retraction
The dynamics and stability of thin liquid films have fascinated scientists
over many decades. Thin film flows are central to numerous areas of
engineering, geophysics, and biophysics and occur over a wide range of length,
velocity, and liquid properties scales. In spite of many significant
developments in this area, we still lack appropriate quantitative experimental
tools with the spatial and temporal resolution necessary for a comprehensive
study of film evolution. We propose tackling this problem with a holographic
technique that combines quantitative phase imaging with a custom setup designed
to form and manipulate bubbles. The results, gathered on a model aqueous
polymeric solution, provide an unparalleled insight into bubble dynamics
through the combination of full-field thickness estimation, three-dimensional
imaging, and fast acquisition time. The unprecedented level of detail offered
by the proposed methodology will promote a deeper understanding of the
underlying physics of thin film dynamics
Least squares DOA estimation with an informed phase unwrapping and full bandwidth robustness
The weighted least-squares (WLS) direction-of-arrival estimator that minimizes an error based on interchannel phase differences is both computationally simple and flexible. However, the approach has several limitations, including an inability to cope with spatial aliasing and a sensitivity to phase wrapping. The recently proposed phase wrapping robust (PWR)-WLS estimator addresses the latter of these issues, but requires solving a nonconvex optimization problem. In this contribution, we focus on both of the described shortcomings. First, a conceptually simpler alternative to PWR is presented that performs comparably given a good initial estimate. This newly proposed method relies on an unwrapping of the phase differences vector. Secondly, it is demonstrated that all microphone pairs can be utilized at all frequencies with both estimators. When incorporating information from other frequency bins, this permits a localization above the spatial aliasing frequency of the array. Experimental results show that a considerable performance improvement is possible, particularly for arrays with a large microphone spacing
Accelerating phase unwrapping and affine transformations for optical quadrature microscopy using CUDA
Optical Quadrature Microscopy (OQM) is a process which uses phase data to capture information about the sample being studied. OQM is part of an imaging framework developed by the Optical Science Laboratory at Northeastern University. In one particular application of interest, the framework is used to extract phase information from the image of an embryo to determine embryo viability. Phase Unwrapping is the process of reconstructing the real phase shift (propagation delay) of a sample from the measured âwrappedâ representation which is between âÏ and +Ï. Unwrapping can be done using the Minimum L P Norm Phase Unwrap algorithm. Images are first preprocessed using an Affine Transform before they are unwrapped. Both of these steps are time consuming and would benefit greatly from parallelization and acceleration. Faster processing would lower many research barriers (in terms of throughpu
Interferometric phase-dispersion microscopy
We describe a new scanning microscopy technique, phase-dispersion microscopy (PDM). The technique is based on measuring the phase difference between the fundamental and the second-harmonic light in a novel interferometer. PDM is highly sensitive to subtle refractive-index differences that are due to dispersion (differential optical path sensitivity, 5 nm). We apply PDM to measure minute amounts of DNA in solution and to study biological tissue sections. We demonstrate that PDM performs better than conventional phase-contrast microscopy in imaging dispersive and weakly scattering samples
Non-paraxial design and fabrication of a compact OAM sorter in the telecom infrared
A novel optical device is designed and fabricated in order to overcome the
limits of the traditional sorter based on log-pol optical transformation for
the demultiplexing of optical beams carrying orbital angular momentum (OAM).
The proposed configuration simplifies the alignment procedure and significantly
improves the compactness and miniaturization level of the optical architecture.
Since the device requires to operate beyond the paraxial approximation, a
rigorous formulation of transformation optics in the non-paraxial regime has
been developed and applied. The sample has been fabricated as 256-level
phase-only diffractive optics with high-resolution electron-beam lithography,
and tested for the demultiplexing of OAM beams at the telecom wavelength of
1310 nm. The designed sorter can find promising applications in next-generation
optical platforms for mode-division multiplexing based on OAM modes both for
free-space and multi-mode fiber transmission.Comment: 12 pages, 8 figure
Automated Fourier space region-recognition filtering for off-axis digital holographic microscopy
Automated label-free quantitative imaging of biological samples can greatly
benefit high throughput diseases diagnosis. Digital holographic microscopy
(DHM) is a powerful quantitative label-free imaging tool that retrieves
structural details of cellular samples non-invasively. In off-axis DHM, a
proper spatial filtering window in Fourier space is crucial to the quality of
reconstructed phase image. Here we describe a region-recognition approach that
combines shape recognition with an iterative thresholding to extracts the
optimal shape of frequency components. The region recognition technique offers
fully automated adaptive filtering that can operate with a variety of samples
and imaging conditions. When imaging through optically scattering biological
hydrogel matrix, the technique surpasses previous histogram thresholding
techniques without requiring any manual intervention. Finally, we automate the
extraction of the statistical difference of optical height between malaria
parasite infected and uninfected red blood cells. The method described here
pave way to greater autonomy in automated DHM imaging for imaging live cell in
thick cell cultures
Tactile whole-field imaging sensor on photoelasticity
The paper describes a whole-field imaging sensor developed on the principles of photoelasticity. The sensor produces colored fringe patterns when load is applied on the contacting surface. These fringes can be analyzed using conventional photoelastic techniques, however, as the loading in the present case is not conventional some new strategies need to be devised to analyze the load imprint. The loading is unconventional in the sense that low modulus photoelastic material is deformed under vertical load in the direction of light travel to induce the photoelastic effect. The paper discusses the efficacy of both RGB calibration and phase shifting techniques in sensing applications. The characteristics of fringe patterns obtained under vertical and shear loads have been studied and the results obtained under these conditions are discussed with their limitations specifically when this is applied for sensing applications. Finally a case study has been conducted to analyze a foot image and conclusions drawn from this have been presented. Copyright © 2007 by ASME
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