5,571 research outputs found
Efficient Computation of Power, Force, and Torque in BEM Scattering Calculations
We present concise, computationally efficient formulas for several quantities
of interest -- including absorbed and scattered power, optical force (radiation
pressure), and torque -- in scattering calculations performed using the
boundary-element method (BEM) [also known as the method of moments (MOM)]. Our
formulas compute the quantities of interest \textit{directly} from the BEM
surface currents with no need ever to compute the scattered electromagnetic
fields. We derive our new formulas and demonstrate their effectiveness by
computing power, force, and torque in a number of example geometries. Free,
open-source software implementations of our formulas are available for download
online
Ab-initio theory of quantum fluctuations and relaxation oscillations in multimode lasers
We present an \emph{ab-initio} semi-analytical solution for the noise
spectrum of complex-cavity micro-structured lasers, including central
Lorentzian peaks at the multimode lasing frequencies and additional sidepeaks
due to relaxation-oscillation (RO) dynamics. In~Ref.~1, we computed the
central-peak linewidths by solving generalized laser rate equations, which we
derived from the Maxwell--Bloch equations by invoking the
fluctuation--dissipation theorem to relate the noise correlations to the
steady-state lasing properties; Here, we generalize this approach and obtain
the entire laser spectrum, focusing on the RO sidepeaks. Our formulation treats
inhomogeneity, cavity openness, nonlinearity, and multimode effects accurately.
We find a number of new effects, including new multimode RO sidepeaks and three
generalized factors. Last, we apply our formulas to compute the noise
spectrum of single- and multimode photonic-crystal lasers.Comment: 27 pages, 3 figure
Speed-of-light limitations in passive linear media
We prove that well-known speed of light restrictions on electromagnetic
energy velocity can be extended to a new level of generality, encompassing even
nonlocal chiral media in periodic geometries, while at the same time weakening
the underlying assumptions to only passivity and linearity of the medium
(either with a transparency window or with dissipation). As was also shown by
other authors under more limiting assumptions, passivity alone is sufficient to
guarantee causality and positivity of the energy density (with no thermodynamic
assumptions). Our proof is general enough to include a very broad range of
material properties, including anisotropy, bianisotropy (chirality),
nonlocality, dispersion, periodicity, and even delta functions or similar
generalized functions. We also show that the "dynamical energy density" used by
some previous authors in dissipative media reduces to the standard Brillouin
formula for dispersive energy density in a transparency window. The results in
this paper are proved by exploiting deep results from linear-response theory,
harmonic analysis, and functional analysis that had previously not been brought
together in the context of electrodynamics.Comment: 19 pages, 1 figur
Numerical Methods for Computing Casimir Interactions
We review several different approaches for computing Casimir forces and related fluctuation-induced interactions between bodies of arbitrary shapes and materials. The relationships between this problem and well known computational techniques from classical electromagnetism are emphasized. We also review the basic principles of standard computational methods, categorizing them according to three criteria\-choice of problem, basis, and solution technique\-that can be used to classify proposals for the Casimir problem as well. In this way, mature classical methods can be exploited to model Casimir physics, with a few important modifications.Keywords:
Imaginary Frequency, Perfectly Match Layer, Casimir Force, Casimir Energy, Perfect Electric ConductorUnited States. Army Research Office (Contract W911NF-07-D-0004)Massachusetts Institute of Technology. Ferry FundUnited States. Defense Advanced Research Projects Agency (Contract N66001-09-1-2070-DOD
Topology optimization of freeform large-area metasurfaces
We demonstrate optimization of optical metasurfaces over --
degrees of freedom in two and three dimensions, 100--1000+ wavelengths
() in diameter, with 100+ parameters per . In particular,
we show how topology optimization, with one degree of freedom per
high-resolution "pixel," can be extended to large areas with the help of a
locally periodic approximation that was previously only used for a few
parameters per . In this way, we can computationally discover
completely unexpected metasurface designs for challenging multi-frequency,
multi-angle problems, including designs for fully coupled multi-layer
structures with arbitrary per-layer patterns. Unlike typical metasurface
designs based on subwavelength unit cells, our approach can discover both sub-
and supra-wavelength patterns and can obtain both the near and far fields
Computation of Casimir Interactions between Arbitrary 3D Objects with Arbitrary Material Properties
We extend a recently introduced method for computing Casimir forces between
arbitrarily--shaped metallic objects [M. T. H. Reid et al., Phys. Rev.
Lett._103_ 040401 (2009)] to allow treatment of objects with arbitrary material
properties, including imperfect conductors, dielectrics, and magnetic
materials. Our original method considered electric currents on the surfaces of
the interacting objects; the extended method considers both electric and
magnetic surface current distributions, and obtains the Casimir energy of a
configuration of objects in terms of the interactions of these effective
surface currents. Using this new technique, we present the first predictions of
Casimir interactions in several experimentally relevant geometries that would
be difficult to treat with any existing method. In particular, we investigate
Casimir interactions between dielectric nanodisks embedded in a dielectric
fluid; we identify the threshold surface--surface separation at which
finite--size effects become relevant, and we map the rotational energy
landscape of bound nanoparticle diclusters
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