1,805 research outputs found
Time for pulse traversal through slabs of dispersive and negative (, ) materials
The traversal times for an electromagnetic pulse traversing a slab of
dispersive and dissipative material with negative dielectric permittivity
() and magnetic permeability () have been calculated by using
the average flow of electromagnetic energy in the medium. The effects of
bandwidth of the pulse and dissipation in the medium have been investigated.
While both large bandwidth and large dissipation have similar effects in
smoothening out the resonant features that appear due to Fabry-P\'{e}rot
resonances, large dissipation can result in very small or even negative
traversal times near the resonant frequencies. We have also investigated the
traversal times and Wigner delay times for obliquely incident pulses and
evanescent pulses. The coupling to slab plasmon polariton modes in frequency
ranges with negative or is shown to result in large traversal
times at the resonant conditions. We also find that the group velocity mainly
contributes to the delay times for pulse propagating across a slab with n=-1.
We have checked that the traversal times are positive and subluminal for pulses
with sufficiently large bandwidths.Comment: 9 pages, 9 figures, Submitted to Phys. Rev.
Effective photon-photon interaction in a two-dimensional "photon fluid"
We formulate an effective theory for the atom-mediated photon-photon
interactions in a two-dimensional ``photon fluid'' confined in a Fabry-Perot
resonator. With the atoms modelled by a collection of anharmonic Lorentz
oscillators, the effective interaction is evaluated to second order in the
coupling constant (the anharmonicity parameter). The interaction has the form
of a renormalized two-dimensional delta-function potential, with the
renormalization scale determined by the physical parameters of the system, such
as density of atoms and the detuning of the photons relative to the resonance
frequency of the atoms. For realistic values of the parameters, the
perturbation series has to be resummed, and the effective interaction becomes
independent of the ``bare'' strength of the anharmonic term. The resulting
expression for the non-linear Kerr susceptibility, is parametrically equal to
the one found earlier for a dilute gas of two-level atoms. Using our result for
the effective interaction parameter, we derive conditions for the formation of
a photon fluid, both for Rydberg atoms in a microwave cavity and for alkali
atoms in an optical cavity.Comment: 25 pages (revtex4), including 2 figure
Can a charged ring levitate a neutral, polarizable object? Can Earnshaw's Theorem be extended to such objects?
Stable electrostatic levitation and trapping of a neutral, polarizable object
by a charged ring is shown to be theoretically impossible. Earnshaw's Theorem
precludes the existence of such a stable, neutral particle trap.Comment: 11 pages, 1 figur
High-performance fiber/epoxy composite pressure vessels
Activities described include: (1) determining the applicability of an ultrahigh-strength graphite fiber to composite pressure vessels; (2) defining the fatigue performance of thin-titanium-lined, high-strength graphite/epoxy pressure vessel; (3) selecting epoxy resin systems suitable for filament winding; (4) studying the fatigue life potential of Kevlar 49/epoxy pressure vessels; and (5) developing polymer liners for composite pressure vessels. Kevlar 49/epoxy and graphite fiber/epoxy pressure vessels, 10.2 cm in diameter, some with aluminum liners and some with alternation layers of rubber and polymer were fabricated. To determine liner performance, vessels were subjected to gas permeation tests, fatigue cycling, and burst tests, measuring composite performance, fatigue life, and leak rates. Both the metal and the rubber/polymer liner performed well. Proportionately larger pressure vessels (20.3 and 38 cm in diameter) were made and subjected to the same tests. In these larger vessels, line leakage problems with both liners developed the causes of the leaks were identified and some solutions to such liner problems are recommended
Signal velocity, causality, and quantum noise in superluminal light pulse propagation
We consider pulse propagation in a linear anomalously dispersive medium where
the group velocity exceeds the speed of light in vacuum (c) or even becomes
negative. A signal velocity is defined operationally based on the optical
signal-to-noise ratio, and is computed for cases appropriate to the recent
experiment where such a negative group velocity was observed. It is found that
quantum fluctuations limit the signal velocity to values less than c.Comment: 4 Journal pages, 3 figure
A new class of trapped light filaments
New class light filament identified in Raman radiation of intense ruby laser bea
A terahertz grid frequency doubler
We present a 144-element terahertz quasi-optical grid frequency doubler. The grid is a planar structure with bow-tie antennas as a unit cell, each loaded with a planar Schottky diode. The maximum output power measured for this grid is 24 mW at 1 THz for 3.1-μs 500-GHz input pulses with a peak input power of 47 W. An efficiency of 0.17% for an input power of 6.3 W and output power of 10.8 mW is measured. To date, this is the largest recorded output power for a multiplier at terahertz frequencies. Input and output tuning curves are presented and an output pattern is measured and compared to theory
- …