14 research outputs found
Second harmonic generation in suspensions of spherical particles
We study the second harmonic generation (SHG) in a suspension of small
spherical particles confined within a slab, assuming undepleted pump and
applying (i) single scattering approximation and (ii) diffusion approximation.
In the case (i), the angular diagram, the differential and total crossections
of the SHG process, as well as the average cosine of SH scattering angle are
calculated. In the case (ii), the average SH intensity is found to show no
explicit dependence on the linear scattering properties of the suspension. The
average intensity of SH wave scales as I_0 L / \Lambda_2 in both cases (i) and
(ii), where I_0 is the intensity of the incident wave, L is the slab thickness,
and \Lambda_2 is an intensity-dependent "SH scattering" length.Comment: PDF, 20 pages, 4 figure
Langevin description of speckle dynamics in nonlinear disordered media
We formulate a Langevin description of dynamics of a speckle pattern
resulting from the multiple scattering of a coherent wave in a nonlinear
disordered medium. The speckle pattern exhibits instability with respect to
periodic excitations at frequencies below some
, provided that the nonlinearity exceeds some
-dependent threshold. A transition of the speckle pattern from a
stationary state to the chaotic evolution is predicted upon increasing
nonlinearity. The shortest typical time scale of chaotic intensity fluctuations
is of the order of .Comment: 6 pages, 3 figure
Monitoring spatially heterogeneous dynamics in a drying colloidal thin film
We report on a new type of experiment that enables us to monitor spatially
and temporally heterogeneous dynamic properties in complex fluids. Our approach
is based on the analysis of near-field speckles produced by light diffusely
reflected from the superficial volume of a strongly scattering medium. By
periodic modulation of an incident speckle beam we obtain pixel-wise ensemble
averages of the structure function coefficient, a measure of the dynamic
activity. To illustrate the application of our approach we follow the different
stages in the drying process of a colloidal thin film. We show that we can
access ensemble averaged dynamic properties on length scales as small as ten
micrometers over the full field of view.Comment: To appear in Soft Material
Saturation induced coherence loss in coherent backscattering of light
We use coherent backscattering (CBS) of light by cold Strontium atoms to
study the mutual coherence of light waves in the multiple scattering regime. As
the probe light intensity is increased, the atomic optical transition starts to
be saturated. Nonlinearities and inelastic scattering then occur. In our
experiment, we observe a strongly reduced enhancement factor of the coherent
backscattering cone when the intensity of the probe laser is increased,
indicating a partial loss of coherence in multiple scattering
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.
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.
Diffusion and Localization of Cold Atoms in 3D Optical Speckle
In this work we re-formulate and solve the self-consistent theory for
localization to a Bose-Einstein condensate expanding in a 3D optical speckle.
The long-range nature of the fluctuations in the potential energy, treated in
the self-consistent Born approximation, make the scattering strongly velocity
dependent, and its consequences for mobility edge and fraction of localized
atoms have been investigated numerically.Comment: 8 pages, 11 figure
Coherent multiple light scattering in Faraday active materials
Wave propagation in multiple scattering media shows various kinds of coherent phenomena such as coherent backscattering [1, 2] or Anderson localization [3], both of which are intimately connected to the concept of reciprocity. Manipulating reciprocity in such media is a powerful tool to study these phenomena in experiments [4]. Here we discuss the manipulation of reciprocity in reflection and transmission geometry for the case of light propagation in magneto-optical media. We show new experiments on coherent backscattering and speckle correlations in strongly scattering samples containing Faraday active materials (CeF3) with transport mean free path in the μm range, at low temperatures (T < 10 K) and high fields (B = 18 T). Under such conditions we observe the effect of a Faraday rotation saturation in multiple scattering measurements.publishe
Mapping of periodically poled crystals via spontaneous parametric down-conversion
A new method for characterization of periodically poled crystals is developed
based on spontaneous parametric down-conversion. The method is demonstrated on
crystals of Y:LiNbO3, Mg:Y:LiNbO3 with non-uniform periodically poled
structures, obtained directly under Czochralski growth procedure and designed
for application of OPO in the mid infrared range. Infrared dispersion of
refractive index, effective working periods and wavelengths of OPO were
determined by special treatment of frequency-angular spectra of spontaneous
parametric down-conversion in the visible range. Two-dimensional mapping via
spontaneous parametric down-conversion is proposed for characterizing spatial
distribution of bulk quasi-phase matching efficiency across the input window of
a periodically poled sample.Comment: 19 pages, 6 figure