95 research outputs found
A two-step method for retrieving the longitudinal profile of an electron bunch from its coherent radiation
The coherent radiation emitted by an electron bunch provides a diagnostic
signal that can be used to estimate its longitudinal distribution. Commonly
only the amplitude of the intensity spectrum can be measured and the associated
phase must be calculated to obtain the bunch profile. Very recently an
iterative method was proposed to retrieve this phase. However ambiguities
associated with non-uniqueness of the solution are always present in the phase
retrieval procedure. Here we present a method to overcome the ambiguity problem
by first performing multiple independent runs of the phase retrieval procedure
and then second, sorting the good solutions by mean of cross-correlation
analysis. Results obtained with simulated bunches of various shapes and
experimental measured spectra are presented, discussed and compared with the
established Kramers-Kronig method. It is shown that even when the effect of the
ambiguities is strong, as is the case for a double peak in the profile, the
cross-correlation post-processing is able to filter out unwanted solutions. We
show that, unlike the Kramers-Kronig method, the combined approach presented is
able to faithfully reconstruct complicated bunch profiles.Comment: 22 pages, 5 figure
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
Statistical Image Reconstruction for High-Throughput Thermal Neutron Computed Tomography
Neutron Computed Tomography (CT) is an increasingly utilised non-destructive
analysis tool in material science, palaeontology, and cultural heritage. With
the development of new neutron imaging facilities (such as DINGO, ANSTO,
Australia) new opportunities arise to maximise their performance through the
implementation of statistically driven image reconstruction methods which have
yet to see wide scale application in neutron transmission tomography. This work
outlines the implementation of a convex algorithm statistical image
reconstruction framework applicable to the geometry of most neutron tomography
instruments with the aim of obtaining similar imaging quality to conventional
ramp filtered back-projection via the inverse Radon transform, but using a
lower number of measured projections to increase object throughput. Through
comparison of the output of these two frameworks using a tomographic scan of a
known 3 material cylindrical phantom obtain with the DINGO neutron radiography
instrument (ANSTO, Australia), this work illustrates the advantages of
statistical image reconstruction techniques over conventional filter
back-projection. It was found that the statistical image reconstruction
framework was capable of obtaining image estimates of similar quality with
respect to filtered back-projection using only 12.5% the number of projections,
potentially increasing object throughput at neutron imaging facilities such as
DINGO eight-fold
Paraxial diffusion-field retrieval
Unresolved spatially-random microstructure, in an illuminated sample, can
lead to position-dependent blur when an image of that sample is taken using an
incoherent imaging system. For a small propagation distance, between the exit
surface of the sample and the entrance surface of a position-sensitive
detector, the paraxial approximation implies that the blurring influence of the
sample may be modeled using an anomalous-diffusion field. This diffusion field
may have a scalar or tensor character, depending on whether the random
microstructure has an autocorrelation function that is rotationally isotropic
or anisotropic, respectively. Partial differential equations are written down
and then solved, in a closed-form manner, for several variants of the inverse
problem of diffusion-field retrieval given suitable intensity images. Both
uniform-illumination and structured-illumination schemes are considered. Links
are made, between the recovered diffusion field and certain statistical
properties of the unresolved microstructure. The developed theory -- which may
be viewed as a crudely parallel form of small-angle scattering under the
Guinier approximation -- is applicable to a range of paraxial radiation and
matter fields, such as visible light, x rays, neutrons, and electrons
Contextual, Optimal and Universal Realization of the Quantum Cloning Machine and of the NOT gate
A simultaneous realization of the Universal Optimal Quantum Cloning Machine
(UOQCM) and of the Universal-NOT gate by a quantum injected optical parametric
amplification (QIOPA), is reported. The two processes, forbidden in their exact
form for fundamental quantum limitations, are found universal and optimal, and
the measured fidelity F<1 is found close to the limit values evaluated by
quantum theory. This work may enlighten the yet little explored
interconnections of fundamental axiomatic properties within the deep structure
of quantum mechanics.Comment: 10 pages, 2 figure
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