2,648 research outputs found
Propagating and evanescent waves in absorbing media
We compare the behavior of propagating and evanescent light waves in
absorbing media with that of electrons in the presence of inelastic scattering.
The imaginary part of the dielectric constant results primarily in an
exponential decay of a propagating wave, but a phase shift for an evanescent
wave. We then describe how the scattering of quantum particles out of a
particular coherent channel can be modeled by introducing an imaginary part to
the potential in analogy with the optical case. The imaginary part of the
potential causes additional scattering which can dominate and actually prevent
absorption of the wave for large enough values of the imaginary part. We also
discuss the problem of maximizing the absorption of a wave and point out that
the existence of a bound state greatly aids absorption. We illustrate this
point by considering the absorption of light at the surface of a metal.Comment: Brief Review, to appear in the American Journal of Physics,
http://www.kzoo.edu/ajp
Sub-wavelength imaging: Resolution enhancement using metal wire gratings
An experimental evidence of subwavelength imaging with a "lens", which is a
uniaxial negative permittivity wire medium slab, is reported. The slab is
formed by gratings of long thin parallel conducting cylinders. Taking into
account the anisotropy and spatial dispersion in the wire medium we
theoretically show that there are no usual plasmons that could be exited on
surfaces of such a slab, and there is no resonant enhancement of evanescent
fields in the slab. The experimentally observed clear improvement of the
resolution in the presence of the slab is explained as filtering out the
harmonics with small wavenumbers. In other words, the wire gratings (the wire
medium) suppress strong traveling-mode components increasing the role of
evanescent waves in the image formation. This effect can be used in near-field
imaging and detection applications.Comment: 12 pages, 6 figure
Diffusion at constant speed in a model phase space
We reconsider the problem of diffusion of particles at constant speed and
present a generalization of the Telegrapher process to higher dimensional
stochastic media (), where the particle can move along directions.
We derive the equations for the probability density function using the
``formulae of differentiation'' of Shapiro and Loginov. The model is an
advancement over similiar models of photon migration in multiply scattering
media in that it results in a true diffusion at constant speed in the limit of
large dimensions.Comment: Final corrected version RevTeX, 6 pages, 1 figur
The conditional tunneling time for reflection using the WKB wave-function
We derive an expression for the conditional time for the reflection of a wave
from an arbitrary potential barrier using the WKB wavefunction in the barrier
region. Our result indicates that the conditional times for transmission and
reflection are equal for a symmetric barrier within the validity of the WKB
approach.Comment: 4 pages RevTeX, 1 eps figure include
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.
Complete controllability of quantum systems
Sufficient conditions for complete controllability of -level quantum
systems subject to a single control pulse that addresses multiple allowed
transitions concurrently are established. The results are applied in particular
to Morse and harmonic-oscillator systems, as well as some systems with
degenerate energy levels. Morse and harmonic oscillators serve as models for
molecular bonds, and the standard control approach of using a sequence of
frequency-selective pulses to address a single transition at a time is either
not applicable or only of limited utility for such systems.Comment: 8 pages, expanded and revised versio
Controlling Metamaterial Resonances with Light
We investigate the use of coherent optical fields as a means of dynamically
controlling the resonant behaviour of a variety of composite metamaterials,
wherein the metamaterial structures are embedded in a dispersive dielectric
medium. Control and switching is implemented by coherently driving the resonant
permittivity of the embedding medium by applied optical radiation. The effect
of embedding Split ring resonators (SRR) in a frequency- dispersive medium with
Lorentz-like dispersion or with dispersion engineered by electromagnetic
induced transparency (EIT), is manifested in the splitting of the negative
permeability band, the modified (frequency-dependent) filling fractions and
dissipation factors. The modified material parameters are strongly linked to
the resonant frequencies of the medium, while for an embedding medium
exhibiting EIT, also to the strength and detuning of the control field. The
robustness of control against the deleterious influence of dissipation
associated with the metallic structures as well as the inhomogeneous broadening
due to structural imperfections is demonstrated. Studies on plasmonic
metamaterials that consist of metallic nanorods arranged in loops and exhibit a
collective magnetic response at optical frequencies are presented. Control and
switching in this class of plasmonic nanorod metamaterials is shown to be
possible, for example, by embedding these arrays in a Raman active liquid like
CS and utilizing the Inverse Raman Effect.Comment: 9 pages, 9 figure
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