6,600 research outputs found
Aberrated dark-field imaging systems
We study generalized dark-field imaging systems. These are a subset of linear
shift-invariant optical imaging systems, that exhibit arbitrary aberrations,
and for which normally-incident plane-wave input yields zero output. We write
down the theory for the forward problem of imaging coherent scalar optical
fields using such arbitrarily-aberrated dark-field systems, and give numerical
examples. The associated images may be viewed as a form of dark-field Gabor
holography, utilizing arbitrary outgoing Green functions as generalized
Huygens-type wavelets, and with the Young-type boundary wave forming the
holographic reference
Phase-and-amplitude recovery from a single phase contrast image using partially spatially coherent X-ray radiation
A simple method of phase-and-amplitude extraction is derived that corrects
for image blurring induced by partially spatially coherent incident
illumination using only a single intensity image as input. The method is based
on Fresnel diffraction theory for the case of high Fresnel number, merged with
the space-frequency description formalism used to quantify partially coherent
fields and assumes the object under study is composed of a single material. A
priori knowledge of the object's complex refractive index and information
obtained by characterizing the spatial coherence of the source is required. The
algorithm was applied to propagation-based phase contrast data measured with a
laboratory-based micro-focus X-ray source. The blurring due to the finite
spatial extent of the source is embedded within the algorithm as a simple
correction term to the so-called Paganin algorithm and is also numerically
stable in the presence of noise
Situations in traffic - how quickly they change
Spatio-temporal correlations of intensity of traffic are analysed for one
week data collected in the motorway M-30 around Madrid in January 2009. We
found that the lifetime of these correlations is the shortest in the evening,
between 6 and 8 p.m. This lifetime is a new indicator how much attention of
drivers is demanded in given traffic conditions.Comment: 9 pages, 6 figure
Aberrations in shift-invariant linear optical imaging systems using partially coherent fields
Here the role and influence of aberrations in optical imaging systems
employing partially coherent complex scalar fields is studied. Imaging systems
require aberrations to yield contrast in the output image. For linear
shift-invariant optical systems, we develop an expression for the output
cross-spectral density under the space-frequency formulation of statistically
stationary partially coherentfields. We also develop expressions for the output
cross{spectral density and associated spectral density for weak-phase,
weak-phase-amplitude, and single-material objects in one transverse spatial
dimension
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