2,018 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
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
Sub-wavelength imaging at optical frequencies using canalization regime
Imaging with sub-wavelength resolution using a lens formed by periodic
metal-dielectric layered structure is demonstrated. The lens operates in
canalization regime as a transmission device and it does not involve negative
refraction and amplification of evanescent modes. The thickness of the lens
have to be an integer number of half-wavelengths and can be made as large as
required for ceratin applications, in contrast to the other sub-wavelength
lenses formed by metallic slabs which have to be much smaller than the
wavelength. Resolution of at 600 nm wavelength is confirmed by
numerical simulation for a 300 nm thick structure formed by a periodic stack of
10 nm layers of glass with and 5 nm layers of metal-dielectric
composite with . Resolution of is predicted for a
structure with same thickness, period and operating frequency, but formed by
7.76 nm layers of silicon with and 7.24 nm layers of silver with
.Comment: 4 pages, 4 figures, submitted to PR
Reliability Testing of AlGaN/GaN HEMTs Under Multiple Stressors
We performed an experiment on AlGaN/GaN HEMTs with high voltage and high power as stressors. We found that devices tested under high power generally degraded more than those tested under high voltage. In particular, the high-voltage-tested devices did not degrade significantly as suggested by some papers in the literature. The same papers in the literature also suggest that high voltages cause cracks and pits. However, the high-voltage-tested devices in this study do not exhibit cracks or pits in TEM images, while the high-power-tested devices exhibit pits
Plasmon polaritons in photonic superlattices containing a left-handed material
We analyze one-dimensional photonic superlattices which alternate layers of
air and a left-handed material. We assume Drude-type dispersive responses for
the dielectric permittivity and magnetic permeability of the left-handed
material. Maxwell's equations and the transfer-matrix technique are used to
derive the dispersion relation for the propagation of obliquely incident
optical fields. The photonic dispersion indicates that the growth-direction
component of the electric (or magnetic) field leads to the propagation of
electric (or magnetic) plasmon polaritons, for either TE or TM configurations.
Furthermore, we show that if the plasma frequency is chosen within the photonic
zeroth-order bandgap, the coupling of light with plasmons
weakens considerably. As light propagation is forbidden in that particular
frequency region, the plasmon-polariton mode reduces to a pure plasmon mode.Comment: 4 pages, 4 figure
A Superlens Based on Metal-Dielectric Composites
Pure noble metals are typically considered to be the materials of choice for
a near-field superlens that allows subwavelength resolution by recovering both
propagating and evanescent waves. However, a superlens based on bulk metal can
operate only at a single frequency for a given dielectric host. In this Letter,
it is shown that a composite metal-dielectric film, with an appropriate metal
filling factor, can operate at practically any desired wavelength in the
visible and near-infrared ranges. Theoretical analysis and simulations verify
the feasibility of the proposed lens.Comment: 15 pages, 4 figure
Limitations on Sub-Diffraction Imaging with a Negative Refractive Index Slab
Recently it has been proposed that a planar slab of material, for which both
the permittivity and permeability have the values of -1, could bring not only
the propagating fields associated with a source to a focus, but could also
refocus the nonpropagating near-fields, thereby achieving a subdiffraction
image. In this work we discuss the sensitivity of the subwavelength focus to
various slab parameters, pointing out the connection to slab plasmon modes. We
also note and resolve a paradox associated with the perfect imaging of a point
source. We conclude that subwavelength resolution is achievable with available
technology, but only by implementation of a critical set of design parameters.Comment: pdf fil
Constructive control of quantum systems using factorization of unitary operators
We demonstrate how structured decompositions of unitary operators can be
employed to derive control schemes for finite-level quantum systems that
require only sequences of simple control pulses such as square wave pulses with
finite rise and decay times or Gaussian wavepackets. To illustrate the
technique it is applied to find control schemes to achieve population transfers
for pure-state systems, complete inversions of the ensemble populations for
mixed-state systems, create arbitrary superposition states and optimize the
ensemble average of dynamic observables.Comment: 28 pages, IoP LaTeX, principal author has moved to Cambridge
University ([email protected]
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