38 research outputs found
Polarizability Expressions for Predicting Resonances in Plasmonic and Mie Scatterers
Polarizability expressions are commonly used in optics and photonics to model
the light scattering by small particles. Models based on Taylor series of the
scattering coefficients of the particles fail to predict the morphologic
resonances hosted by dielectric particles. Here, we propose to use the
factorization of the special functions appearing in the expression of the Mie
scattering coefficients to derive point-like models. These models can be
applied to reproduce both Mie resonances of dielectric particles and plasmonic
resonances of metallic particles. They provide simple but robust tools to
predict accurately the electric and magnetic Mie resonances in dielectric
particles.Comment: 11 pages, 7 figure
Modal Expansion of the Scattered Field: Causality, Non-Divergence and Non-Resonant Contribution
Modal analysis based on the quasi-normal modes (QNM), also called resonant
states, has emerged as a promising way for modeling the resonant interaction of
light with open optical cavities. However, the fields associated with QNM in
open photonic cavities diverge far away from the scatterer and the possibility
of expanding the scattered field with resonant contributions only has not been
established. Here, we address these two issues while restricting our study to
the case of a dispersionless spherical scatterer. First, we derive the rigorous
pole expansion of the -matrix coefficients that link the scattered to the
incident fields associated with an optical resonator. This expansion evinces
the existence of a non-resonant term. Second, in the time domain, the causality
principle allows us to solve the problem of divergence and to derive a modal
expansion of the scattered field that does not diverge far from the scatterer
Enhanced Purcell factor for nanoantennas supporting interfering resonances
We study the effect of coupled resonances and quasi-bound states in the
continuum (quasi-BICs) on the Purcell factor in dielectric resonant
nanoantennas. We analyze numerically interfering resonances in a nanodisk with
and without a substrate when the modes are coupled to an emitter localized
inside the nanodisk, and we quantify the modal contributions to the Purcell
factor also reconstructing the radiation patterns of the resonant system. It is
revealed that the Purcell effect can be boosted substantially for a strong
coupling of resonances in the quasi-BIC regime
Poles and zeros in non-Hermitian systems: Application to photonics
Resonances are essential for understanding the interactions between light and
matter in photonic systems. The real frequency response of the non-Hermitian
systems depends on the complex-valued resonance frequencies, which are the
poles of electromagnetic response functions. The zeros of the response
functions are often used for designing devices, since the zeros can be located
close to the real axis, where they have significant impact on scattering
properties. While methods are available to determine the locations of the
poles, there is a lack of appropriate approaches to find the zeros in photonic
systems. We present an approach to compute poles and zeros based on contour
integration of electromagnetic quantities. This also allows to extract
sensitivities with respect to geometrical or other parameters enabling
efficient device design. The approach is applied to a topical example in
nanophotonics, an illuminated metasurface, where the emergence of reflection
zeros due to the underlying resonance poles is explored using residue-based
modal expansions. The generality and simplicity of the theory allows
straightforward transfer to other areas of physics. We expect that easy access
to zeros will enable new computer-aided design methods in photonics and other
fields
Multiple-Order Singularity Expansion Method
Physical systems and signals are often characterized by complex functions of
frequency in the harmonic-domain. The extension of such functions to the
complex frequency plane has been a topic of growing interest as it was shown
that specific complex frequencies could be used to describe both ordinary and
exceptional physical properties. In particular, expansions and factorized forms
of the harmonic-domain functions in terms of their poles and zeros under
multiple physical considerations have been used. In this work, we start from a
general property of continuity and differentiability of the complex functions
to derive the multiple-order singularity expansion method. We rigorously derive
the common singularity and zero expansion and factorization expressions, and
generalize them to the case of singularities of arbitrary order, whilst
deducing the behaviour of these complex frequencies from the simple hypothesis
that we are dealing with physically realistic signals.Comment: Main manuscript: 13 pages, 5 figures. Supporting information: 6
pages, 3 figure
Optimal interactions of light with magnetic and electric resonant particles
This work studies the limits of far and near-field electromagnetic response
of sub-wavelength scatterers, like the unitary limit and of lossless
scatterers, and the ideal absorption limit of lossy particles. These limit
behaviors are described in terms of analytic formulas that approximate finite
size effects while rigorously including radiative corrections. This analysis
predicts the electric and/or magnetic limit responses of both metallic and
dielectric nanoparticles while quantitatively describing near-field
enhancements.Comment: 9 pages, 8 figures, 2 table
Type-3 Secretion System-induced pyroptosis protects Pseudomonas against cell-autonomous immunity
Inflammasome-induced pyroptosis comprises a key cell-autonomous immune process against intracellular bacteria, namely the generation of dying cell structures. These so-called pore-induced intracellular traps (PITs) entrap and weaken intracellular microbes. However, the immune importance of pyroptosis against extracellular pathogens remains unclear. Here, we report that Type-3 secretion system (T3SS)-expressing Pseudomonas aeruginosa ( P. aeruginosa ) escaped PIT immunity by inducing a NLRC4 inflammasome-dependent macrophage pyroptosis response in the extracellular environment. To the contrary, phagocytosis of Salmonella Typhimurium promoted NLRC4-dependent PIT formation and the subsequent bacterial caging. Remarkably, T3SS-deficient Pseudomonas were efficiently sequestered within PIT-dependent caging, which favored exposure to neutrophils. Conversely, both NLRC4 and caspase-11 deficient mice presented increased susceptibility to T3SS-deficient P. aeruginosa challenge, but not to T3SS-expressing P. aeruginosa. Overall, our results uncovered that P. aeruginosa uses its T3SS to overcome inflammasome-triggered pyroptosis, which is primarily effective against intracellular invaders. Importance Although innate immune components confer host protection against infections, the opportunistic bacterial pathogen Pseudomonas aeruginosa ( P. aeruginosa ) exploits the inflammatory reaction to thrive. Specifically the NLRC4 inflammasome, a crucial immune complex, triggers an Interleukin (IL)-1β and -18 deleterious host response to P. aeruginosa . Here, we provide evidence that, in addition to IL-1 cytokines, P. aeruginosa also exploits the NLRC4 inflammasome-induced pro-inflammatory cell death, namely pyroptosis, to avoid efficient uptake and killing by macrophages. Therefore, our study reveals that pyroptosis-driven immune effectiveness mainly depends on P. aeruginosa localization. This paves the way toward our comprehension of the mechanistic requirements for pyroptosis effectiveness upon microbial infections and may initiate targeted approaches in order to ameliorate the innate immune functions to infections. Graphical abstract Macrophages infected with T3SS-expressing P. aeruginosa die in a NLRC4-dependent manner, which allows bacterial escape from PIT-mediated cell-autonomous immunity and neutrophil efferocytosis. However, T3SS-deficient P. aeruginosa is detected by both NLRC4 and caspase-11 inflammasomes, which promotes bacterial trapping and subsequent efferocytosis of P. aeruginosa -containing-PITs by neutrophils
Roadmap on photonic metasurfaces
Funding: C.R. and U.L. acknowledge support through the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany’s Excellence Strategy via the Excellence Cluster 3D Matter Made to Order (EXC-2082/1, Grant No. 390761711). A.B.E. acknowledges support through the Cluster of Excellence PhoenixD (EXC 2122, Project ID No. 390833453). I.F.-C. and C.R. acknowledge support through the CRC Waves: Analysis and Numerics (SFB 1173, Grant No. 258734477. K.A. acknowledges funding from the Swiss National Science Foundation (Project No. PZ00P2_193221).Here we present a roadmap on Photonic metasurfaces. This document consists of a number of perspective articles on different applications, challenge areas or technologies underlying photonic metasurfaces. Each perspective will introduce the topic, present a state of the art as well as give an insight into the future direction of the subfield.Peer reviewe
Novel Insights on the Field Enhancements and Time dynamics in All-Dielectric Antennas through their Quasinormal Modes
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