12,063 research outputs found
Characteristics of bound modes in coupled dielectric waveguides containing negative index media
We investigate the characteristics of guided wave modes in planar coupled
waveguides. In particular, we calculate the dispersion relations for TM modes
in which one or both of the guiding layers consists of negative index media
(NIM)-where the permittivity and permeability are both negative. We find that
the Poynting vector within the NIM waveguide axis can change sign and
magnitude, a feature that is reflected in the dispersion curves
Storage by trapping and spatial staggering of multiple interacting solitons in -type media
In this paper we investigate the properties of self induced transparency
(SIT) solitons, propagating in a -type medium. It was found that the
interaction between SIT solitons can lead to trapping with their phase
preserved in the ground state coherence of the medium. These phases can be
altered in a systematic way by the application of appropriate light fields,
such as additional SIT solitons. Furthermore, multiple independent SIT solitons
can be made to propagate as bi-solitons through their mutual interaction with a
separate light field. Finally, we demonstrate that control of the SIT soliton
phase can be used to implement an optical exclusive-or gate.Comment: 7 pages, 7 figure
Electron bunch injection at an angle into a laser wakefield
External injection of electron bunches longer than the plasma wavelength in a
laser wakefield accelerator can lead to the generation of femtosecond
ultrarelativistic bunches with a couple of percent energy spread. Extensive
study has been done on external electron bunch (e.g. one generated by a
photo-cathode rf linac) injection in a laser wakefield for different
configurations. In this paper we investigate a new way of external injection
where the electron bunch is injected at a small angle into the wakefield. This
way one can avoid the ponderomotive scattering as well as the vacuum-plasma
transition region, which tend to destroy the injected bunch. In our
simulations, the effect of the laser pulse dynamics is also taken into account.
It is shown that injection at an angle can provide compressed and accelerated
electron bunches with less than 2% energy spread. Another advantage of this
scheme is that it has less stringent requirements in terms of the size of the
injected bunch and there is the potential to trap more charge
Ultrafast, low-power, all-optical switching via birefringent phase-matched transverse mode conversion in integrated waveguides
We demonstrate the potential of birefringence-based, all-optical, ultrafast
conversion between the transverse modes in integrated optical waveguides by
modelling the conversion process by numerically solving the multi-mode coupled
nonlinear Schroedinger equations. The observed conversion is induced by a
control beam and due to the Kerr effect, resulting in a transient index grating
which coherently scatters probe light from one transverse waveguide mode into
another. We introduce birefringent phase matching to enable efficient
all-optically induced mode conversion at different wavelengths of the control
and probe beam. It is shown that tailoring the waveguide geometry can be
exploited to explicitly minimize intermodal group delay as well as to maximize
the nonlinear coefficient, under the constraint of a phase matching condition.
The waveguide geometries investigated here, allow for mode conversion with over
two orders of magnitude reduced control pulse energy compared to previous
schemes and thereby promise nonlinear mode switching exceeding efficiencies of
90% at switching energies below 1 nJ
Characterization of Microbial Activity
The overall goal of this study is to investigate the phenomena that affect the fate and transport of radionuclides in the environment. The objective of this task, “Characterization of Microbial Activity”, is to develop a molecular biological method for the characterization of the microbial population indigenous to the Yucca Mountain Project site, with emphasis in detection and measurement of species or groups of microorganisms that could be involved in actinide and/or metal reduction, and subsurface transport. Subtasks consist of QA planning and preparation, and literature review. This task is part of a cooperative agreement between the UNLV Research Foundation and the U.S. Department of Energy (#DE-FC28-04RW12237) titled “Yucca Mountain Groundwater Characterization”
The cool end of the DZ sequence in the SDSS
We report the discovery of cool DZ white dwarfs, which lie in the SDSS (u-g)
vs. (g-r) two-color diagram across and below the main sequence. These stars
represent the extension of the well-known DZ sequence towards cooler
temperatures.Comment: To appear in the proceedings of the "17th European Workshop on White
Dwarfs", Tuebingen, Germany, August 16-20, 201
Frequency stability of a self-phase-locked degenerate continuous-wave optical parametric oscillator
The properties of a self-phase-locked by-2-divider optical parametric oscillator are presented. A locking range of up to 156 MHz is measured, and the divider's relative frequency stability is shown to be better than 6/spl times/10/sup -14/
Plasmonic Resonances and Electromagnetic Forces Between Coupled Silver Nanowires
We compute the electromagnetic response and corresponding forces between two
silver nanowires. The wires are illuminated by a plane wave which has the
electric field vector perpendicular to the axis of the wires, insuring that
plasmonic resonances can be excited. We consider a nontrivial square cross
section geometry that has dimensions on the order of , where
is the wavelength of the incident electromagnetic field. We find that
due to the plasmonic resonance, there occurs great enhancement of the direct
and mutual electromagnetic forces that are exerted on the nanowires. The
Lippman-Schwinger volume integral equation is implemented to obtain solutions
to Maxwell's equations for various and separation distances between
wires. The forces are computed using Maxwell's stress tensor and numerical
results are shown for both on and off resonant conditions
Production of Neutral Pions and Eta-mesons in pp Collisions Measured with ALICE
Invariant cross sections for neutral pions and eta mesons in pp collisions at
sqrt(s) = 0.9, 2.76, and 7 TeV were measured by the ALICE detector at the Large
Hadron Collider. Next-to-leading order (NLO) perturbative QCD calculations
describe the pi0 and eta spectra at 0.9 TeV, but overestimate the measured
cross sections at 2.76 TeV and 7 TeV. The measured eta/pi0 ratio is consistent
with mT scaling at 2.76 TeV. At 7 TeV indications for a violation of mT scaling
were found.Comment: 4 pages, 2 figures, to appear in the proceedings of the XXII
International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions,
Quark Matter 2011, Annec
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