1,781 research outputs found
Impact of interparticle dipole-dipole interactions on optical nonlinearity of nanocomposites
In this paper, effect of dipole-dipole interactions on nonlinear optical
properties of the system of randomly located semiconductor nanoparticles
embedded in bulk dielectric matrix is investigated. This effect results from
the nonzero variance of the net dipole field in an ensemble. The analytical
expressions describing the contribution of the dipole-dipole coupling to
nonlinear dielectric susceptibility are obtained. The derived relationships are
applicable over the full range of nanoparticle volume fractions. The factors
entering into the contribution and depending on configuration of the dipoles
are calculated for several cases. It is shown that for the different
arrangements of dipole alignments the relative change of this contribution does
not exceed 1/3.Comment: 5 pages, 1 figur
Possibility of negative refraction for visible light in disordered all-dielectric resonant high index metasurfaces
Effective refractive index of disordered all-dielectric metasurfaces
consisting of gallium phosphide (GaP) spheres is studied by means of
three-dimensional finite-difference time-domain (FDTD) simulations at the
wavelength of 532~nm. It is shown that a mixture of the high index
nanoparticles with sizes close to the first magnetic and electric resonances
randomly dispersed on metasurface may possess negative refraction. The
dependence of the metasurface effective refractive index on the nanoparticle
concentration and size is constructed. The feasibility of negative refraction
at large concentrations of the high index resonant spheres is demonstrated. The
negative effective refractive index is exhibited only for a monolayer of GaP
spheres.Comment: 7 pages, 6 figures, 1 tabl
Giant enhancement and sign inversion of optical Kerr nonlinearity in random high index nanocomposites near Mie resonances
High index dielectric nanoantennas excited at Mie-type resonances have
exhibited enormous enhancement of optical nonlinearity. Such nanostructures
have been actively studied by researchers in the last years. The present work
provides the first numerical analysis study of the optical Kerr effect of
nanocomposites consisting of high refractive index (GaP) spheres at the
wavelength of 532~nm. This is done by means of three-dimensional
finite-difference time-domain (FDTD) simulations. The effective nonlinear
refractive index of ~m thick nanocomposites and metasurfaces is
evaluated. It is shown that the optical Kerr nonlinearity of the nanocomposites
rises by orders in proximity to Mie resonances and may exceed the second-order
refractive index of the bulk material. It is revealed that the sign of the
effective optical Kerr coefficient is inverted near the Mie resonances. This
effect may be of interest in developing nonlinear optical metadevices.Comment: 8 pages, 7 figures, 2 table
Retrieving nonlinear refractive index of nanocomposites using finite-difference time-domain simulations
In this Letter, it is proposed a method which utilizes three-dimensional
finite-difference time-domain (FDTD) simulations of light propagation for
restoring the effective Kerr nonlinearity of nanocomposite media. In this
approach, a dependence of the phase shift of the transmitted light on the input
irradiance is exploited. The reconstructed values of the real parts of the
nonlinear refractive index of a structure of randomly arranged spheres are in
good agreement with the predictions of the effective medium approximations.Comment: 4 pages, 2 figures, 2 table
Optical Kerr nonlinearity of disordered all-dielectric resonant high index metasurfaces with negative refraction
The optical Kerr effect of material with negative refraction is estimated for
the first time. This is done via three-dimensional finite-difference
time-domain (FDTD) simulations of disordered bidisperse metasurfaces consisting
of high index (GaP) spheres at the wavelength of 532~nm. The metasurfaces
comprise spherical particles randomly arranged on plane having two sizes close
to the magnetic and electric dipole Mie resonances. The real part of the
effective nonlinear refractive index of the metasurfaces is computed in the
vicinity of the Mie resonances where the metasurface possesses the negative
index of refraction. The optical Kerr nonlinearity has a peak under the
condition for the negative refraction. Intensity-dependent refractive index of
the bidisperse metasurfaces is studied through concentration transition to the
negative refraction state. It is shown that the nonlinear Kerr coefficient of
the monolayer metasurface has maximum when the effective linear refractive
index is close to zero.Comment: 5 pages, 4 figure
Reconstructing signal from fiber-optic measuring system with non-linear perceptron
A computer model of the feed-forward neural network with the hidden layer is
developed to reconstruct physical field investigated by the fiber-optic
measuring system. The Gaussian distributions of some physical quantity are
selected as learning patterns. Neural network is learned by error
back-propagation using the conjugate gradient and coordinate descent
minimization of deviation. Learned neural network reconstructs the
two-dimensional scalar physical field with distribution having one or two
Gaussian peaks.Comment: 3 pages, Latex, 1 postscript figur
Multivariate subordination of stable processes
This article is devoted to some time-changed stochastic models based on
multivariate stable processes. The considered models have several advantages in
comparison with classical time-changed Brownian motions - for instance, it
turns out that they are more appropriate for describing stock prices if the
amount of transactions is used for a stochastic time change. In this paper, we
provide a detailed discussion of the model, which is based on two popular
concepts - multivariate subordination and L{\'e}vy copulas.Comment: 2
Coadjoint orbits of the group
We present the classification of coadjoint orbits of the unitriangular group
. We also describe subregular orbits of for an arbitrary
.Comment: 27 page
Subregular characters of the group UT(n,R)
The formulas for subregular characters of the unitriangular Lie group are
obtained. The supports of regular and subregular characters are described in
terms of the orbit method.Comment: 14 page
Dipolar induced anisotropy in the random-field Ising model
The crystalline ferromagnet with dipole-dipole interactions is studied within
the framework of the three-dimensional random-field Ising model. The field
distribution function and the analytic expression for temperature dependent
free energy are found. The dipolar induced magnetic anisotropy energy of bulk
cubic ferromagnetic materials is calculated.Comment: LaTeX, 3 page
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