3,805 research outputs found
Self-consistent calculation of metamaterials with gain
We present a computational scheme allowing for a self-consistent treatment of
a dispersive metallic photonic metamaterial coupled to a gain material
incorporated into the nanostructure. The gain is described by a generic
four-level system. A critical pumping rate exists for compensating the loss of
the metamaterial. Nonlinearities arise due to gain depletion beyond a certain
critical strength of a test field. Transmission, reflection, and absorption
data as well as the retrieved effective parameters are presented for a lattice
of resonant square cylinders embedded in layers of gain material and split ring
resonators with gain material embedded into the gaps.Comment: 5 pages, 6 figure
Single-cycle gap soliton in a subwavelength structure
We demonstrate that a single sub-cycle optical pulse can be generated when a
pulse with a few optical cycles penetrates through resonant two-level dense
media with a subwavelength structure. The single-cycle gap soliton phenomenon
in the full Maxwell-Bloch equations without the frame of slowly varying
envelope and rotating wave approximations is observed. Our study shows that the
subwavelength structure can be used to suppress the frequency shift caused by
intrapulse four-wave mixing in continuous media and supports the formation of
single-cycle gap solitons even in the case when the structure period breaks the
Bragg condition. This suggests a way toward shortening high-intensity laser
fields to few- and even single-cycle pulse durations.Comment: 4 pages, 6 figure
Carrier-envelope phase dependence in single-cycle laser pulse propagation with the inclusion of counter-rotating terms
We focus on the propagation properties of a single-cycle laser pulse through
a two-level medium by numerically solving the full-wave Maxwell-Bloch
equations. The counter-rotating terms in the spontaneous emission damping are
included such that the equations of motion are slightly different from the
conventional Bloch equations. The counter-rotating terms can considerably
suppress the broadening of the pulse envelope and the decrease of the group
velocity rooted from dispersion. Furthermore, for incident single-cycle pulses
with envelope area 4, the time-delay of the generated soliton pulse from
the main pulse depends crucially on the carrier-envelope phase of the incident
pulse. This can be utilized to determine the carrier-envelope phase of the
single-cycle laser pulse.Comment: 6 pages, 5 figure
Numerical calculations of effective elastic properties of two cellular structures
Young's moduli of regular two-dimensional truss-like and eye-shape-like
structures are simulated by using the finite element method. The structures are
the idealizations of soft polymeric materials used in the electret
applications. In the simulations size of the representative smallest units are
varied, which changes the dimensions of the cell-walls in the structures. A
power-law expression with a quadratic as the exponential term is proposed for
the effective Young's moduli of the systems as a function of the solid volume
fraction. The data is divided into three regions with respect to the volume
fraction; low, intermediate and high concentrations. The parameters of the
proposed power-law expression in each region are later represented as a
function of the structural parameters, unit-cell dimensions. The presented
expression can be used to predict structure/property relationship in materials
with similar cellular structures. It is observed that the structures with
volume fractions of solid higher than 0.15 exhibit the importance of the
cell-wall thickness contribution in the elastic properties. The cell-wall
thickness is the most significant factor to predict the effective Young's
modulus of regular cellular structures at high volume fractions of solid. At
lower concentrations of solid, eye-like structure yields lower Young's modulus
than the truss-like structure with the similar anisotropy. Comparison of the
numerical results with those of experimental data of poly(propylene) show good
aggreement regarding the influence of cell-wall thickness on elastic properties
of thin cellular films.Comment: 7 figures and 2 table
Numerical Investigation of Light Scattering off Split-Ring Resonators
Recently, split ring-resonators (SRR's) have been realized experimentally in
the near infrared (NIR) and optical regime. In this contribution we numerically
investigate light propagation through an array of metallic SRR's in the NIR and
optical regime and compare our results to experimental results.
We find numerical solutions to the time-harmonic Maxwell's equations by using
advanced finite-element-methods (FEM). The geometry of the problem is
discretized with unstructured tetrahedral meshes. Higher order, vectorial
elements (edge elements) are used as ansatz functions. Transparent boundary
conditions and periodic boundary conditions are implemented, which allow to
treat light scattering problems off periodic structures.
This simulation tool enables us to obtain transmission and reflection spectra
of plane waves which are incident onto the SRR array under arbitrary angles of
incidence, with arbitrary polarization, and with arbitrary
wavelength-dependencies of the permittivity tensor. We compare the computed
spectra to experimental results and investigate resonances of the system.Comment: 9 pages, 8 figures (see original publication for images with a better
resolution
2335 Evaluation of anterior chamber angle: Gonioscopy, ultrasound biomicroscopy and scheimpflug photography
Aprovat per la Comissió de Govern de 10-09-2014El termini de la suspensió serà , com a mà xim, d'un any, a comptar des de l'endemà de la publicació al BO
The rise of (Chiral) 3D mechanical metamaterials
On the occasion of this special issue, we start by briefly outlining some of the history and future perspectives of the field of 3D metamaterials in general and 3D mechanical metamaterials in particular. Next, in the spirit of a specific example, we present our original numerical as well as experimental results on the phenomenon of acoustical activity, the mechanical counterpart of optical activity. We consider a three-dimensional chiral cubic mechanical metamaterial architecture that is different from the one that we have investigated in recent early experiments. We find even larger linear-polarization rotation angles per metamaterial crystal lattice constant than previously and a slower decrease of the effects towards the bulk lim
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