367 research outputs found
Complexity of Polarized Spatial Patterns in Large Area Square VCSEL
We consider pattern selection process in a wide aperture VCSEL near
threshold. We show that for a square geometry of the laser aperture, the
patterns formed at lasing threshold can be very complicated because of a
possible misalignment between directions of an intrinsic spatial anisotropy of
VCSEL and lateral boundaries of its aperture. The analogy with quantum billiard
structures is established, and fingerprints of wave chaos are found. Influence
of localized inhomogeneous in the pump current is also considered.Comment: 10 pages, 8 figures, uses REVTEX
Bistability conditions between lasing and non-lasing states for vertical-cavity surface-emitting lasers with frequency-selective optical feedback
This paper gives analytical treatment and experimental details on on/off-bistability in vertical-cavity surface-emitting lasers with frequency-selective feedback by a grating. In particular, the conditions for the coexistence of lasing and nonlasing states and an abrupt turn-on behaviour at threshold are derived using an envelope approximation. The theoretical and experimental results are in satisfactory agreement
Optical vault: reconfigurable bottle beam by conically refracted light
We employ conical refraction of light in a biaxial crystal to create an
optical bottle for trapping and manipulation of particles. We show that by just
varying the polarization of the input light the bottle can be opened and closed
at will. We experimentally demonstrate stable photophoretic trapping and
controllable loading and unloading of light absorbing particles in the trap.Comment: 4 pages, 5 figure
Wave-vector and polarization dependence of conical refraction
We experimentally address the wave-vector and polarization dependence of the
internal conical refraction phenomenon by demonstrating that an input light
beam of elliptical transverse profile refracts into two beams after passing
along one of the optic axes of a biaxial crystal, i.e. it exhibits double
refraction instead of refracting conically. Such double refraction is
investigated by the independent rotation of a linear polarizer and a
cylindrical lens. Expressions to describe the position and the intensity
pattern of the refracted beams are presented and applied to predict the
intensity pattern for an axicon beam propagating along the optic axis of a
biaxial crystal
gauged boson stars in the Einstein-Friedberg-Lee-Sirlin model
We consider spherically symmetric gauged boson stars in the
two-component scalar Friedberg-Lee-Sirlin model with a symmetry breaking
potential in 3+1 dimensional spacetime. Depending on the relative strength of
gravity and the electromagnetic interaction, the resulting boson stars exhibit
either the typical properties of ungauged boson stars, or their behavior
resembles the pattern found for gauged Q-balls of the Friedberg-Lee-Sirlin
model in flat spacetime, both for a finite and a vanishing potential.Comment: 18 pages, 8 figure
Drifting instabilities of cavity solitons in vertical cavity surface-emitting lasers with frequency selective feedback
In this paper we study the formation and dynamics of self-propelled cavity
solitons (CSs) in a model for vertical cavity surface-emitting lasers (VCSELs)
subjected to external frequency selective feedback (FSF), and build their
bifurcation diagram for the case where carrier dynamics is eliminated. For low
pump currents, we find that they emerge from the modulational instability point
of the trivial solution, where traveling waves with a critical wavenumber are
formed. For large currents, the branch of self-propelled solitons merges with
the branch of resting solitons via a pitchfork bifurcation. We also show that a
feedback phase variation of 2\pi can transform a CS (whether resting or moving)
into a different one associated to an adjacent longitudinal external cavity
mode. Finally, we investigate the influence of the carrier dynamics, relevant
for VCSELs. We find and analyze qualitative changes in the stability properties
of resting CSs when increasing the carrier relaxation time. In addition to a
drifting instability of resting CSs, a new kind of instability appears for
certain ranges of carrier lifetime, leading to a swinging motion of the CS
center position. Furthermore, for carrier relaxation times typical of VCSELs
the system can display multistability of CSs.Comment: 11 pages, 12 figure
Polarization tailored novel vector beams based on conical refraction
Coherent vector beams with involved states of polarization (SOP) are
widespread in the literature, having applications in laser processing,
super-resolution imaging and particle trapping. We report novel vector beams
obtained by transforming a Gaussian beam passing through a biaxial crystal, by
means of the conical refraction phenomenon. We analyze both experimentally and
theoretically the SOP of the different vector beams generated and demonstrate
that the SOP of the input beam can be used to control both the shape and the
SOP of the transformed beam. We also identify polarization singularities of
such beams for the first time and demonstrate their control by the SOP of an
input beam
Neural networks for aerosol particles characterization
© 2016 Elsevier LtdMultilayer perceptron neural networks with one, two and three inputs are built to retrieve parameters of spherical homogeneous nonabsorbing particle. The refractive index ranges from 1.3 to 1.7; particle radius ranges from 0.251 μm to 56.234 μm. The logarithms of the scattered radiation intensity are used as input signals. The problem of the most informative scattering angles selection is elucidated. It is shown that polychromatic illumination helps one to increase significantly the retrieval accuracy. In the absence of measurement errors relative error of radius retrieval by the neural network with three inputs is 0.54%, relative error of the refractive index retrieval is 0.84%. The effect of measurement errors on the result of retrieval is simulated
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