177 research outputs found
Localization of transverse waves in randomly layered media at oblique incidence
We investigate the oblique incidence of transverse waves on a randomly
layered medium in the limit of strong disorder. An approximate method for
calculating the inverse localization length based on the assumptions of zero
energy flux and complete phase stochastization is presented. Two effects not
found at normal incidence have been studied: dependence of the localization
length on the polarization, and decrease of the localization length due to the
internal reflections from layers with small refractive indexes. The inverse
localization length (attenuation rate) for P-polarized radiation is shown to be
always smaller than that of S-waves, which is to say that long enough randomly
layered sample polarizes transmitted radiation. The localization length for
P-polarization depends non-monotonically on the angle of propagation, and under
certain conditions turns to infinity at some angle, which means that typical
(non-resonant) random realizations become transparent at this angle of
incidence (stochastic Brewster effect).Comment: 12 pages, 1 figure, accepted for publication in Physical Review
Localized Modes in Open One-Dimensional Dissipative Random Systems
We consider, both theoretically and experimentally, the excitation and
detection of the localized quasi-modes (resonances) in an open dissipative 1D
random system. We show that even though the amplitude of transmission drops
dramatically so that it cannot be observed in the presence of small losses,
resonances are still clearly exhibited in reflection. Surprisingly, small
losses essentially improve conditions for the detection of resonances in
reflection as compared with the lossless case. An algorithm is proposed and
tested to retrieve sample parameters and resonances characteristics inside the
random system exclusively from reflection measurements.Comment: 5 pages, 3 figures, to appear in Phys. Rev. Let
Resonances in 1D disordered systems: localization of energy and resonant transmission
Localized states in one-dimensional open disordered systems and their
connection to the internal structure of random samples have been studied. It is
shown that the localization of energy and anomalously high transmission
associated with these states are due to the existence inside the sample of a
transparent (for a given resonant frequency) segment with the minimal size of
order of the localization length. A mapping of the stochastic scattering
problem in hand onto a deterministic quantum problem is developed. It is shown
that there is no one-to-one correspondence between the localization and high
transparency: only small part of localized modes provides the transmission
coefficient close to one. The maximal transmission is provided by the modes
that are localized in the center, while the highest energy concentration takes
place in cavities shifted towards the input. An algorithm is proposed to
estimate the position of an effective resonant cavity and its pumping rate by
measuring the resonant transmission coefficient. The validity of the analytical
results have been checked by extensive numerical simulations and wavelet
analysis
Total absorption of an electromagnetic wave by an overdense plasma
We show both theoretically and experimentally that an electromagnetic wave
can be totally absorbed by an overdense plasma when a subwavelength diffraction
grating is placed in front of the plasma surface. The absorption is due to
dissipation of surface plasma waves (plasmons-polaritons) that have been
resonantly excited by the evanescent component of the diffracted
electromagnetic wave. The developed theoretical model allows one to determine
the conditions for the total absorption.Comment: To be published in PR
Electron Beam Instability in Left-Handed Media
We predict that two electron beams can develop an instability when passing
through a slab of left-handed media (LHM). This instability, which is inherent
only for LHM, originates from the backward Cherenkov radiation and results in a
self-modulation of the beams and radiation of electromagnetic waves. These
waves leave the sample via the rear surface of the slab (the beam injection
plane) and form two shifted bright circles centered at the beams. A simulated
spectrum of radiation has well-separated lines on top of a broad continuous
spectrum, which indicates dynamical chaos in the system. The radiation
intensity and its spectrum can be controlled either by the beams' current or by
the distance between the two beams.Comment: 4 pages, 4 figure
Transverse Shifts in Paraxial Spinoptics
The paraxial approximation of a classical spinning photon is shown to yield
an "exotic particle" in the plane transverse to the propagation. The previously
proposed and observed position shift between media with different refractive
indices is modified when the interface is curved, and there also appears a
novel, momentum [direction] shift. The laws of thin lenses are modified
accordingly.Comment: 3 pages, no figures. One detail clarified, some misprints corrected
and references adde
Spatio-temporal vortex beams and angular momentum
We present a space-time generalization of the known spatial (monochromatic)
wave vortex beams carrying intrinsic orbital angular momentum (OAM) along the
propagation direction. Generic spatio-temporal vortex beams are polychromatic
and can carry intrinsic OAM at an arbitrary angle to the mean momentum.
Applying either (i) a transverse wave-vector shift or (ii) a Lorentz boost to a
monochromatic Bessel beam, we construct a family of either (i) time-diffracting
or (ii) non-diffracting spatio-temporal Bessel beams, which are exact solutions
of the Klein-Gordon wave equations. The proposed spatio-temporal OAM states are
able to describe either photon or electron vortex states (both relativistic and
nonrelativistic), and can find applications in particle collisions, optics of
moving media, quantum communications, and astrophysics.Comment: 9 pages, 6 figures, to appear in Phys. Rev.
Millimeter Wave Localization: Slow Light and Enhanced Absorption
We exploit millimeter wave technology to measure the reflection and
transmission response of random dielectric media. Our samples are easily
constructed from random stacks of identical, sub-wavelength quartz and Teflon
wafers. The measurement allows us to observe the characteristic transmission
resonances associated with localization. We show that these resonances give
rise to enhanced attenuation even though the attenuation of homogeneous quartz
and Teflon is quite low. We provide experimental evidence of disorder-induced
slow light and superluminal group velocities, which, in contrast to photonic
crystals, are not associated with any periodicity in the system. Furthermore,
we observe localization even though the sample is only about four times the
localization length, interpreting our data in terms of an effective cavity
model. An algorithm for the retrieval of the internal parameters of random
samples (localization length and average absorption rate) from the external
measurements of the reflection and transmission coefficients is presented and
applied to a particular random sample. The retrieved value of the absorption is
in agreement with the directly measured value within the accuracy of the
experiment.Comment: revised and expande
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