38 research outputs found
Nonuniversal correlations in multiple scattering
We show that intensity of a wave created by a source embedded inside a
three-dimensional disordered medium exhibits a non-universal space-time
correlation which depends explicitly on the short-distance properties of
disorder, source size, and dynamics of disorder in the immediate neighborhood
of the source. This correlation has an infinite spatial range and is
long-ranged in time. We suggest that a technique of "diffuse microscopy" might
be developed employing spatially-selective sensitivity of the considered
correlation to the disorder properties.Comment: 15 pages, 3 postscript figures, accepted to Phys. Rev.
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INVESTIGATION OF MULTI-MATERIAL LIQUID METAL JETTING WITH COPPER MATERIALS
Technical parts are typically subject to various requirements that may conflict with each
other. Multi-material parts can be a way to overcome such conflicting goals. Liquid Metal Jetting
(LMJ) can be a promising additive manufacturing process for the production of multi-material
copper parts with high geometric complexity. Since LMJ builds up a part droplet by droplet, there
are no mixed powders after printing. In addition, LMJ offers the possibility of changing materials
from droplet to droplet. In previous studies, we have shown that it is possible to produce copper
alloy parts using LMJ. In this work, we produced multi-material copper specimens at different
process parameters to investigate the manufacturing of multi-material copper parts. The
investigations show that the quality of the compound and the microstructure depend significantly
on the thermal process parameters used.Mechanical Engineerin
Time-Resolved Diffusing Wave Spectroscopy for selected photon paths beyond 300 transport mean free paths
This paper is devoted to the theoretical and experimental demonstration of
the possibility to perform time-resolved diffusing wave spectroscopy: we
successfully registered field fluctuations for selected photon path lengths
that can overpass 300 transport mean free paths. Such a performance opens new
possibilities for biomedical optics applications.Comment: 12 pages, 3 figure
Diffusing-wave spectroscopy of nonergodic media
We introduce an elegant method which allows the application of diffusing-wave
spectroscopy (DWS) to nonergodic, solid-like samples. The method is based on
the idea that light transmitted through a sandwich of two turbid cells can be
considered ergodic even though only the second cell is ergodic. If absorption
and/or leakage of light take place at the interface between the cells, we
establish a so-called "multiplication rule", which relates the intensity
autocorrelation function of light transmitted through the double-cell sandwich
to the autocorrelation functions of individual cells by a simple
multiplication. To test the proposed method, we perform a series of DWS
experiments using colloidal gels as model nonergodic media. Our experimental
data are consistent with the theoretical predictions, allowing quantitative
characterization of nonergodic media and demonstrating the validity of the
proposed technique.Comment: RevTeX, 12 pages, 6 figures. Accepted for publication in Phys. Rev.
Probing helium interfaces with light scattering : from fluid mechanics to statistical physics
We have investigated the formation of helium droplets in two physical
situations. In the first one, droplets are atomised from superfluid or normal
liquid by a fast helium vapour flow. In the second, droplets of normal liquid
are formed inside porous glasses during the process of helium condensation. The
context, aims, and results of these experiments are reviewed, with focus on the
specificity of light scattering by helium. In particular, we discuss how, for
different reasons, the closeness to unity of the index of refraction of helium
allows in both cases to minimise the problem of multiple scattering and obtain
results which it would not be possible to get using other fluids.Comment: 21 page
Temporal fluctuations of waves in weakly nonlinear disordered media
We consider the multiple scattering of a scalar wave in a disordered medium
with a weak nonlinearity of Kerr type. The perturbation theory, developed to
calculate the temporal autocorrelation function of scattered wave, fails at
short correlation times. A self-consistent calculation shows that for
nonlinearities exceeding a certain threshold value, the multiple-scattering
speckle pattern becomes unstable and exhibits spontaneous fluctuations even in
the absence of scatterer motion. The instability is due to a distributed
feedback in the system "coherent wave + nonlinear disordered medium". The
feedback is provided by the multiple scattering. The development of instability
is independent of the sign of nonlinearity.Comment: RevTeX, 15 pages (including 5 figures), accepted for publication in
Phys. Rev.
Time-resolved diffusing wave spectroscopy applied to dynamic heterogeneity imaging
We report in this paper what is to our knowledge the first observation of a
time-resolved diffusing wave spectroscopy signal recorded by transillumination
through a thick turbid medium: the DWS signal is measured for a fixed photon
transit time, which opens the possibility of improving the spatial resolution.
This technique could find biomedical applications, especially in mammography.Comment: 9 pages, 4 figure
Visualization of flow in multiple-scattering liquids
We have performed quasi-elastic multiple-light-scattering experiments on a
suspension of colloidal particles in Brownian motion into which a capillary
with Poiseuille flow of the same suspension was inserted. We show that the
time correlation function of the backscattered light, measured at various
points on the sample surface, provides information on the position
of the capillary and on the flow rate, demonstrating the possibility of
imaging
flow in turbid media under conditions of no static scattering contrast