1,767 research outputs found
Properties of the Quarter-Wave Bragg Reflection Waveguide: Theory
The Bragg reflection waveguide (BRW), or one-dimensional photonic crystal waveguide, has recently been proposed for a wide spectrum of applications ranging from particle acceleration to nonlinear frequency conversion. Here, we conduct a thorough analytical investigation of the quarter-wave BRW, in which the layers of the resonant cladding have a thickness corresponding to one quarter of the transverse wavelength of a desired guided mode. An analytical solution to the mode dispersion equation is derived, and it is shown that the quarter-wave BRW is polarization degenerate, although the TE and TM mode profiles differ significantly as the external Brewster’s angle condition in the cladding is approached. Analytical expressions for waveguide properties such as the modal normalization constants, propagation loss, and overlap factors between the mode and each waveguide layer are derived, as are dispersion and tuning curves
Optical Second Harmonic Generation in Anisotropic Multilayers with Complete Multireflection Analysis of Linear and Nonlinear Waves using #SHAARP.ml Package
Optical second harmonic generation (SHG) is a nonlinear optical effect widely
used for nonlinear optical microscopy and laser frequency conversion.
Closed-form analytical solution of the nonlinear optical responses is essential
for evaluating the optical responses of new materials whose optical properties
are unknown a priori. A recent open-source code, SHAARP(si), can provide such
closed form solutions for crystals with arbitrary symmetries, orientations, and
anisotropic properties at a single interface. However, optical components are
often in the form of slabs, thin films on substrates, and multilayer
heterostructures with multiple reflections of both the fundamental and up to
ten different SHG waves at each interface, adding significant complexity. Many
approximations have therefore been employed in the existing analytical
approaches, such as slowly varying approximation, weak reflection of the
nonlinear polarization, transparent medium, high crystallographic symmetry,
Kleinman symmetry, easy crystal orientation along a high-symmetry direction,
phase matching conditions and negligible interference among nonlinear waves,
which may lead to large errors in the reported material properties. To avoid
these approximations, we have developed an open-source package named Second
Harmonic Analysis of Anisotropic Rotational Polarimetry in Multilayers
(SHAARP(ml)). The reliability and accuracy are established by experimentally
benchmarking with both the SHG polarimetry and Maker fringes predicted from the
package using standard materials
Local-field corrected van der Waals potentials in magnetodielectric multilayer systems
Within the framework of macroscopic quantum electrodynamics in linear, causal
media, we study the van der Waals potentials of ground-state atoms in planar
magnetodielectric host media. Our investigation extends earlier ones in two
aspects: It allows for the atom to be embedded in a medium, thus covers many
more realistic systems; and it takes account of the local-field correction.
Two- and three-layer configurations are treated in detail both analytically and
numerically. It is shown that an interplay of electric and magnetic properties
in neighbouring media may give rise to potential wells or walls. Local-field
corrections as high as 80% are found. By calculating the full potential
including the translationally invariant and variant parts, we propose a way to
estimate the (finite) value of the dispersion potential at the surface between
two media. Connection with earlier work intended for biological applications is
established.Comment: 12 pages, 5 figure
Analysis and Design of a Cylindrical EBG based directive antenna
9 pages.International audienceIn this paper, a cylindrical electromagnetic bandgap (CEBG) structure composed of infinite metallic wires is analyzed, designed and used as a model to develop a new reconfigurable directive antenna. This structure is circularly and radially periodic, and it is excited at its center using an omnidirectional source. The analysis is based on calculating the transmission and reflection coefficients of a single cylindrical frequency selective surface (FSS) and then, considering only the fundamental mode interaction, deducing the frequency response of the CEBG structure composed of multiple cylindrical FSSs. For this structure, new analytical formulas are derived, and their accuracy is assessed compared to those obtained by the finite-difference time-domain method. As in rectangularly periodic structure case, the frequency response of the CEBG structure exhibits pass-bands and bandgaps, and it is possible to obtain directive beams by introducing defects in the periodic structure. Using this concept, a new antenna was developed to obtain a controllable directive beam. An antenna prototype, without control, was designed, fabricated, and tested. An excellent agreement was obtained between theory and experiment for both return loss and radiation patterns
An Efficient Algorithm for Automatic Structure Optimization in X-ray Standing-Wave Experiments
X-ray standing-wave photoemission experiments involving multilayered samples
are emerging as unique probes of the buried interfaces that are ubiquitous in
current device and materials research. Such data require for their analysis a
structure optimization process comparing experiment to theory that is not
straightforward. In this work, we present a new computer program for optimizing
the analysis of standing-wave data, called SWOPT, that automates this
trial-and-error optimization process. The program includes an algorithm that
has been developed for computationally expensive problems: so-called black-box
simulation optimizations. It also includes a more efficient version of the Yang
X-ray Optics Program (YXRO) [Yang, S.-H., Gray, A.X., Kaiser, A.M., Mun, B.S.,
Sell, B.C., Kortright, J.B., Fadley, C.S., J. Appl. Phys. 113, 1 (2013)] which
is about an order of magnitude faster than the original version. Human
interaction is not required during optimization. We tested our optimization
algorithm on real and hypothetical problems and show that it finds better
solutions significantly faster than a random search approach. The total
optimization time ranges, depending on the sample structure, from minutes to a
few hours on a modern laptop computer, and can be up to 100x faster than a
corresponding manual optimization. These speeds make the SWOPT program a
valuable tool for realtime analyses of data during synchrotron experiments
Invisibility and PT Symmetry: A Simple Geometrical Viewpoint
We give a simplified account of the properties of the transfer matrix for a
complex one-dimensional potential, paying special attention to the particular
instance of unidirectional invisibility. In appropriate variables, invisible
potentials appear as performing null rotations, which lead to the
helicity-gauge symmetry of massless particles. In hyperbolic geometry, this can
be interpreted, via M\"{o}bius transformations, as parallel displacements, a
geometric action that has no Euclidean analogy.Comment: 13 pages. No figure. Accepted for publication in Symmetr
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