410 research outputs found
Solitary waves in three-dimensional crystal-like structures
The motion of three-dimensional (3D) solitary waves and solitons in nonlinear
crystal-like structures, such as photonic materials, is studied. It is
demonstrated that collective excitations in these systems can be tailored to
move in particular directions of the 3D system. The effect of modulation
instability is studied showing that in some cases it can be delayed by using a
lensing factor. Analytical results supported by numerical simulations are
presented.Comment: 4 page
Universal Features of the Time Evolution of Evanescent Modes in a Left-Handed Perfect Lens
The time evolution of evanescent modes in Pendry's perfect lens proposal for
ideally lossless and homogeneous, left-handed materials is analyzed. We show
that time development of sub-wavelength resolution exhibits universal features,
independent of model details. This is due to the unavoidable near-degeneracy of
surface electromagnetic modes in the deep sub-wavelength region. By means of a
mechanical analog, it is shown that an intrinsic time scale (missed in
stationary studies) has to be associated with any desired lateral resolution. A
time-dependent cut-off length emerges, removing the problem of divergences
claimed to invalidate Pendry's proposal.Comment: 4 pages, 3 figures, title slightly changed, reference added, minor
correction
Nonlinear properties of left-handed metamaterials
We analyze nonlinear properties of microstructured materials with negative
refraction, the so-called left-handed metamaterials. We consider a
two-dimensional periodic structure created by arrays of wires and split-ring
resonators embedded into a nonlinear dielectric, and calculate the effective
nonlinear electric permittivity and magnetic permeability. We demonstrate that
the hysteresis-type dependence of the magnetic permeability on the field
intensity allows changing the material from left- to right-handed and back.
These effects can be treated as the second-order phase transitions in the
transmission properties induced by the variation of an external field.Comment: 4 pages, 3 figure
Enhanced parametric processes in binary metamaterials
We suggest double-resonant (binary) metamaterials composed of two types of
magnetic resonant elements, and demonstrate that in the nonlinear regime such
metamaterials provide unique possibilities for phase-matched parametric
interaction and enhanced second-harmonic generation
Refraction at Media with Negative Refractive Index
We show that an electromagnetic (EM) wave undergoes negative refraction at
the interface between a positive and negative refractive index material. Finite
difference time domain (FDTD) simulations are used to study the time evolution
of an EM wave as it hits the interface. The wave is trapped temporarily at the
interface and after a long time, the wave front moves eventually in the
negative direction. This explains why causality and speed of light are not
violated in spite of the negative refraction always present in a negative index
material.Comment: 5 pages, 4 figures, submitted to Phys. Rev. Let
Finite-size effects of a left-handed material slab on the image quality
The characteristics of an imaging system formed by a left-handed material
(LHM) slab of finite length are studied, and the influence of the finite length
of the slab on the image quality is analyzed. Unusual phenomena such as surface
bright spots and negative energy stream at the image side are observed and
explained as the cavity effects of surface plasmons excited by the evanescent
components of the incident field. For a thin LHM slab, the cavity effects are
found rather sensitive to the length of the slab, and the bright spots on the
bottom surface of the slab may stretch to the image plane and degrade the image
quality.Comment: changes in the content and the title, and also the figure
Reverse Doppler effect in backward spin waves scattered on acoustic waves
We report on the observation of reverse Doppler effect in backward spin waves
reflected off of surface acoustic waves. The spin waves are excited in a
yttrium iron garnet (YIG) film. Simultaneously, acoustic waves are also
generated. The strain induced by the acoustic waves in the magnetostrictive YIG
film results in the periodic modulation of the magnetic anisotropy in the film.
Thus, in effect, a travelling Bragg grating for the spin waves is produced. The
backward spin waves reflecting off of this grating exhibit a reverse Doppler
shift: shifting down rather than up in frequency when reflecting off of an
approaching acoustic wave. Similarly, the spin waves are shifted up in
frequency when reflecting from receding acoustic waves.Comment: 4 pages, 3 figure
Near Field Lenses in Two Dimensions
It has been shown that a slab of materials with refractive index = -1 behaves
like a perfect lens focussing all light to an exact electromagnetic copy of an
object. The original lens is limited to producing images the same size as the
object, but here we generalise the concept so that images can be magnified. For
two dimensional systems, over distances much shorter than the free space
wavelength, we apply conformal transformations to the original parallel sided
slab generating a variety of new lenses. Although the new lenses are not
`perfect' they are able to magnify two dimensional objects. The results apply
equally to imaging of electric or magnetic sub wavelength objects in two
dimensions. The concepts have potential applications ranging from microwave
frequencies to the visible.Comment: PDF fil
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