231 research outputs found
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
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
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
Isotropic three-dimensional left-handed meta-materials
We investigate three-dimensional left-handed and related meta-materials based
on a fully symmetric multi-gap single-ring SRR design and crossing continuous
wires. We demonstrate isotropic transmission properties of a SRR-only
meta-material and the corresponding left-handed material which possesses a
negative effective index of refraction due to simultaneously negative effective
permeability and permittivity. Minor deviations from complete isotropy are due
to the finite thickness of the meta-material.Comment: 4 pages, 6 figure
Effective medium theory of left-handed materials
We analyze the transmission and reflection data obtained through transfer
matrix calculations on metamaterials of finite lengths, to determine their
effective permittivity and permeability. Our study concerns metamaterial
structures composed of periodic arrangements of wires, cut-wires, split ring
resonators (SRRs), closed-SRRs, and both wires and SRRs. We find that the SRRs
have a strong electric response, equivalent to that of cut-wires, which
dominates the behavior of left-handed materials (LHM). Analytical expressions
for the effective parameters of the different structures are given, which can
be used to explain the transmission characteristics of LHMs. Of particular
relevance is the criterion introduced by our studies to identify if an
experimental transmission peak is left- or right-handed.Comment: to be published in Phys. Rev. Let
A right-handed isotropic medium with a negative refractive index
The sign of the refractive index of any medium is soley determined by the
requirement that the propagation of an electromagnetic wave obeys Einstein
causality. Our analysis shows that this requirement predicts that the real part
of the refractive index may be negative in an isotropic medium even if the
electric permittivity and the magnetic permeability are both positive. Such a
system may be a route to negative index media at optical frequencies. We also
demonstrate that the refractive index may be positive in left-handed media that
contain two molecular species where one is in its excited state.Comment: 4.1 pages, 4 figures, submitted to Physical Review Letter
Negative Refraction and Left-handed electromagnetism in Microwave Photonic Crystals
We demonstrate negative refraction of microwaves in metallic photonic
crystals. The spectral response of the photonic crystal, which manifests both
positive and negative refraction, is in complete agreement with band-structure
calculations and numerical simulations. The negative refraction observed
corresponds to left-handed electromagnetism and arises due to the dispersion
characteristics of waves in a periodic medium. This mechanism for negative
refraction is different from that in metamaterials.Comment: 13 pages, 4 figure
Absolute negative refraction and imaging of unpolarized electromagnetic waves by two-dimensional photonic crystals
Absolute negative refraction regions for both polarizations of
electromagnetic wave in two-dimensional photonic crystal have been found
through both the analysis and the exact numerical simulation. Especially,
absolute all-angle negative refraction for both polarizations has also been
demonstrated. Thus, the focusing and image of unpolarized light can be realized
by a microsuperlens consisting of the two-dimensional photonic crystals. The
absorption and compensation for the losses by introducing optical gain in these
systems have also been discussed
Magnetic metamaterials at telecommunication and visible frequencies
Arrays of gold split-rings with 50-nm minimum feature size and with an LC
resonance at 200-THz frequency (1500-nm wavelength) are fabricated. For normal
incidence conditions, they exhibit a pronounced fundamental magnetic mode,
arising from a coupling via the electric component of the incident light. For
oblique incidence, a coupling via the magnetic component is demonstrated as
well. Moreover, we identify a novel higher-order magnetic resonance at around
370 THz (800-nm wavelength) that evolves out of the Mie resonance for oblique
incidence. Comparison with theory delivers good agreement and also shows that
the structures allow for a negative magnetic permeability.Comment: 4 pages, 3 figure
On the physical origins of the negative index of refraction
The physical origins of negative refractive index are derived from a dilute
microscopic model, producing a result that is generalized to the dense
condensed phase limit. In particular, scattering from a thin sheet of electric
and magnetic dipoles driven above resonance is used to form a fundamental
description for negative refraction. Of practical significance, loss and
dispersion are implicit in the microscopic model. While naturally occurring
negative index materials are unavailable, ferromagnetic and ferroelectric
materials provide device design opportunities.Comment: 4 pages, 1 figur
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