229 research outputs found
The eigenpairs of a Sylvester-Kac type matrix associated with a simple model for one-dimensional deposition and evaporation
A straightforward model for deposition and evaporation on discrete cells of a
finite array of any dimension leads to a matrix equation involving a
Sylvester-Kac type matrix. The eigenvalues and eigenvectors of the general
matrix are determined for an arbitrary number of cells. A variety of models to
which this solution may be applied are discussed.Comment: 7 pages, no figure
Polarization switching and induced birefringence in InGaAsP multiple quantum wells at 1.5 mu m
We analyze the 1.5mum wavelength operation of a room temperature polarization switch based on electron spin dynamics in InGaAsP multiple quantum wells. An unexpected difference in response for left and right circularly polarized pump light in pump-probe measurements was discovered and determined to be caused by an excess carrier induced birefringence. Transient polarization rotation and ellipticity were measured as a function of time delay. (C) 2002 American Institute of Physics.</p
Spatial dependence of gain nonlinearities in InGaAs semiconductor optical amplifier
Counter-propagating sub-picosecond pulses are used to monitor gain saturation along the waveguide of an InGaAs superlattice semiconductor optical amplifier at 1550 nm wavelength. The functional form of the spatial dependence of gain saturation is found to depend on pulse energy. These observations are interpreted by combining the optical nonlinearities associated with interband carrier dynamics and carrier heating together and their respective time constants. We show that the results are consistent with the predictions of a propagation model. Implications for all-optical switching, particularly in the limit of full saturation across the whole amplifier, are discussed. (c) 2005 American Institute of Physics.</p
Exploiting lens aberrations to create electron vortex beams
A model for a new electron vortex beam production method is proposed and
experimentally demonstrated. The technique calls on the controlled manipulation
of the degrees of freedom of the lens aberrations to achieve a helical phase
front. These degrees of freedom are accessible by using the corrector lenses of
a transmission electron microscope. The vortex beam is produced through a
particular alignment of these lenses into a specifically designed astigmatic
state and applying an annular aperture in the condensor plane. Experimental
results are found to be in good agreement with simulations.Comment: 5 pages, 4 figure
Three-dimensional spatiotemporal optical solitons in nonlocal nonlinear media
We demonstrate the existence of stable three-dimensional spatiotemporal
solitons (STSs) in media with a nonlocal cubic nonlinearity. Fundamental
(nonspinning) STSs forming one-parameter families are stable if their
propagation constant exceeds a certain critical value, that is inversely
proportional to the range of nonlocality of nonlinear response. All spinning
three-dimensional STSs are found to be unstable.Comment: 14 pages, 6 figures, accepted to PRE, Rapid Communication
Stable three-dimensional spinning optical solitons supported by competing quadratic and cubic nonlinearities
We show that the quadratic interaction of fundamental and second harmonics in
a bulk dispersive medium, combined with self-defocusing cubic nonlinearity,
give rise to completely localized spatiotemporal solitons (vortex tori) with
vorticity s=1. There is no threshold necessary for the existence of these
solitons. They are found to be stable against small perturbations if their
energy exceeds a certain critical value, so that the stability domain occupies
about 10% of the existence region of the solitons. We also demonstrate that the
s=1 solitons are stable against very strong perturbations initially added to
them. However, on the contrary to spatial vortex solitons in the same model,
the spatiotemporal solitons with s=2 are never stable.Comment: latex text, 10 ps and 2 jpg figures; Physical Review E, in pres
Green-function Method for Nonlinear Interactions of Elastic Waves
In the linear wave propagation regime, an analytical
mesh-free Green-function decomposition has been shown as a
viable alternative to FDTD and FEM. However, its expansion into
nonlinear regimes has remained elusive due to the inherent linear
properties of the Green-function approach. This work presents
a novel frequency-domain Green function method to describe
and model nonlinear wave interactions in isotropic hyperelastic
media. As an example of the capabilities of the method, we
detail the generation of sum frequency waves when initial quasimonochromatic waves are emitted in a fluid by finite sources.
The method is supported by both numerical and experimental
results using immersion ultrasonic techniques
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