scholarly journals Near-field to far-field characterization of speckle patterns generated by disordered nanomaterials

2016 ◽  
Vol 24 (7) ◽  
pp. 7019 ◽  
Author(s):  
Valentina Parigi ◽  
Elodie Perros ◽  
Guillaume Binard ◽  
Céline Bourdillon ◽  
Agnès Maître ◽  
...  
Keyword(s):  
Near Field ◽  
Far Field ◽  
Speckle Patterns

scholarly journals Imaging with Local Speckle Intensity Correlations: Theory and Practice

2021 ◽  
Vol 40 (3) ◽  
pp. 1-22
Author(s):  
Marina Alterman ◽  
Chen Bar ◽  
Ioannis Gkioulekas ◽  
Anat Levin
Keyword(s):  
Near Field ◽  
Biological Tissues ◽  
Computational Imaging ◽  
Theory And Practice ◽  
Fluorescent Imaging ◽  
Light Sources ◽  
Far Field ◽  
Scattering Layer ◽  
Speckle Patterns ◽  
Field Imaging

Recent advances in computational imaging have significantly expanded our ability to image through scattering layers such as biological tissues by exploiting the auto-correlation properties of captured speckle intensity patterns. However, most experimental demonstrations of this capability focus on the far-field imaging setting, where obscured light sources are very far from the scattering layer. By contrast, medical imaging applications such as fluorescent imaging operate in the near-field imaging setting, where sources are inside the scattering layer. We provide a theoretical and experimental study of the similarities and differences between the two settings, highlighting the increased challenges posed by the near-field setting. We then draw insights from this analysis to develop a new algorithm for imaging through scattering that is tailored to the near-field setting by taking advantage of unique properties of speckle patterns formed under this setting, such as their local support. We present a theoretical analysis of the advantages of our algorithm and perform real experiments in both far-field and near-field configurations, showing an order-of magnitude expansion in both the range and the density of the obscured patterns that can be recovered.

Miniaturized beamsplitters realized by X-ray waveguides

2016 ◽  
Vol 72 (5) ◽  
pp. 515-522 ◽  
Author(s):  
Sarah Hoffmann-Urlaub ◽  
Tim Salditt
Keyword(s):  
Interference Pattern ◽  
Phase Retrieval ◽  
Near Field ◽  
Retrieval Algorithm ◽  
Far Field ◽  
X Ray ◽  
Reconstructed Field ◽  
Propagation Methods ◽  
Cladding Material

This paper reports on the fabrication and characterization of X-ray waveguide beamsplitters. The waveguide channels were manufactured by electron-beam lithography, reactive ion etching and wafer bonding techniques, with an empty (air) channel forming the guiding layer and silicon the cladding material. A focused synchrotron beam is efficiently coupled into the input channel. The beam is guided and split into two channels with a controlled (and tunable) distance at the exit of the waveguide chip. After free-space propagation and diffraction broadening, the two beams interfere and form a double-slit interference pattern in the far-field. From the recorded far-field, the near-field was reconstructed by a phase retrieval algorithm (error reduction), which was found to be extremely reliable for the two-channel setting. By numerical propagation methods, the reconstructed field was then propagated along the optical axis, to investigate the formation of the interference pattern from the two overlapping beams. Interestingly, phase vortices were observed and analysed.

Box-Scan: A Novel 3DXRD Method for Studies of Recrystallization and Grain Growth

2012 ◽  
Vol 715-716 ◽  
pp. 518-520 ◽  
Author(s):  
Allan Lyckegaard ◽  
Henning Friis Poulsen ◽  
Wolfgang Ludwig ◽  
Richard W. Fonda ◽  
Erik M. Lauridsen
Keyword(s):  
Spatial Resolution ◽  
Near Field ◽  
Polycrystalline Materials ◽  
High Temporal Resolution ◽  
Far Field ◽  
X Ray Diffraction ◽  
The Individual ◽  
Individual Grains ◽  
Non Destructive

Within the last decade a number of x-ray diffraction methods have been presented for non-destructive 3D characterization of polycrystalline materials. 3DXRD [1] and Diffraction Contrast Tomography [2,3,4] are examples of such methods providing full spatial and crystallographic information of the individual grains. Both methods rely on specially designed high-resolution near-field detectors for acquire the shape of the illuminated grains, and therefore the spatial resolution is for both methods limited by the resolution of the detector, currently ~2 micrometers. Applying these methods using conventional far-field detectors provides information on centre of mass, crystallographic orientation and stress state of the individual grains [5], at the expense of high spatial resolution. However, far-field detectors have much higher efficiency than near-field detectors, and as such are suitable for dynamic studies requiring high temporal resolution and set-ups involving bulky sample environments (e.g. furnaces, stress-rigs etc.)

scholarly journals The Comparison of Seismic Effects of Near-field and Far-field Earthquakes on Relative Displacement of Seven-storey Concrete Building with Shear Wall

2015 ◽  
Vol 10 (Special-Issue1) ◽  
pp. 40-46 ◽  
Author(s):  
Mahdi Heydari ◽  
Mahdi Mousavi
Keyword(s):  
Near Field ◽  
Shear Wall ◽  
Incremental Dynamic Analysis ◽  
Relative Displacement ◽  
Far Field ◽  
The Past ◽  
Concrete Building ◽  
Structural Behaviors ◽  
Storey Building

In the past few years, numerous studies on the effects of near-field earthquakes on the response of structures and their differences with far-field earthquakes imply the attention of researchers to this issue. In this regard, the objectives of present study are to study the effects of near-field earthquakes on the behavior of structures and to compare these types of earthquakes with far-field ones. To do this, the characterization of near-field earthquakes and their descriptions are used to define the differences between near-field and far-field earthquakes in regard to radically distinctive responses of structures. In the present study, the incremental dynamic analysis of a seven-storey building with concrete structure for few near-field and far-field earthquakes is done and the associated diagrams of relative structural displacement are compared. In the end, the comparison of these plots is used to denote the differences in the structural behaviors of these two types of earthquakes.

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