Vadim MARKEL

Unidirectional modes in chains of plasmonic particles

Surface plasmon polaritons (SPPs) in chains of plasmonic nanoparticles have attracted significant attention due to potential applications in spectroscopy, sensing, and subwavelength manipulation of electromagnetic energy. On aspect of such waveguides that received relatively little attention is directionality. In the talks I will discuss waveguides with a sense of direction. Such waveguides are not invariant under the reflection of the z-axis (with which the waveguide is aligned). I will show that, although the dispersion relations in directional waveguides are still symmetric as is required by the electromagnetic reciprocity, a localized excitation applied to a central part of the chain can selectively couple to the SPPs propagating in only one of the two possible directions.

Francesco CHIADINI, Roberta DE SIMONE, Vincenzo FIUMARA, and Akhlesh LAKHTAKIA

Tightly Interlaced Matched Ambidextrous Bilayer material for enhancement of performances in optical devices

The quest for novel materials with peculiar characteristics – both physical and mechanical – for innovative and increasingly high-performance devices is constantly evolving. Many promising complex nano-engineered materials, e.g. with nano-inclusions or nano-layers, and so on, have been proposed and studied. Among these innovative materials, we draw attention to the Tightly Interlaced Matched Ambidextrous Bilayer (TIMAB) which is a periodically non-homogeneous nano-structured material consisting of two chiral materials that are structurally identical except for their handedness that flips at the center of the unit cell. We shall present the optical characteristics of TIMABs in two different cases: (i) for surface-plasmon-polariton (SPP) waves propagating at the planar interface of a metal and a TIMAB to increase the number of SPP waves with superluminal phase speed, and (ii) the plane-wave reflection/transmission characteristics of multilayers comprising a chirped TIMAB to increase the bandgap.

Vincenzo GALDI

Some perspectives in line-wave electromagnetics

Line waves are recently discovered wave objects that can propagate along suitably designed planar impedance discontinuities, thereby effectively channeling electromagnetic power along one-dimensional pathways. In this overview, we summarize the findings from both recent and ongoing investigations in this emerging field. The scope encompasses phenomenological and modeling aspects, shedding light on potential applications that may arise from this intriguing phenomenon.

Vincenzo FIUMARA, Francesco CHIADINI, Roberta DE SIMONE et al.

On the coatings for mirrors of gravitational wave interferometric detectors

In the last decade, direct observation of gravitational waves has become a reality thanks to long-baseline laser interferometer detectors with kilometric arms. The coatings of the interferometer end masses are requested to exhibit high optical reflectance, low optical absorption (and scattering), and low mechanical losses (directly related to thermal noise, in view of the fluctuation-dissipation principle). Indeed, the thermal noise is an important cause limiting the detector sensitivity and visibility range. The coatings of the currently operating interferometers consist of alternating layers of silica (low refractive index) and titania-doped tantala (high refractive index). Realizing better performing coatings still remains a scientific and technological challenge. In first part of this presentation the problem of designing high-performance ternary coatings, where a third material is added to the two presently in use, is addressed. The second part will be focused on nano-engineered materials for coatings of 3rd-generation gravitational detectors operating at cryogenic temperature.

Olivier J. F. MARTIN

A non-linear, non-reciprocal (?) metasurface

We demonstrate experimentally a metasurface built from Ag and Al meta-atoms, which exhibits a very peculiar nonlinear response: upon illumination from one side, it produces a very strong second harmonic response, while this is not at all the case for illumination from the other side. I will discuss the underlying mechanisms that lead to this effect, especially the role of bi-anisotropy both at the fundamental and second harmonic frequencies. The linear and non-linear susceptibilities of the system can be retrieved from numerical simulations. I will also discuss whether this device is reciprocal or not.

Ibrahim ABDULHALIM

Resonant versus non-resonant metamaterial structures for light modulation, sensing, and energy saving

Recently we have been developing various devices tailored for sensing, energy conservation, and light modulation applications. These innovations encompass surface plasmon resonance and surface-enhanced Raman scattering (SERS) sensors designed to detect biological and chemical contaminants, including explosive materials. In particular, the coupling between extended and localized plasmons is utilized for explosives sensing with SERS. Additionally, we will explore subwavelength grating structures integrated with liquid crystals to serve as tunable achromatic waveplates, nanoporous microparticles embedded within liquid crystals for intelligent window functionalities, and nanoporous metamaterial surfaces engineered to regulate thermal influx into buildings, thereby optimizing energy efficiency.
Acknowledgment: This research is performed within the project titled “Nanomaterials for explosive traces detection with SERS” (NOOSE), funded by NATO Science for Peace and Security Programme under contract number MYP G5814. The project is partially funded by the Israel Ministry of Science and Technology as well as the Ministry of Energy and Infrastructure.

Andrei V. LAVRINENKO

Nanogratings in sensing applications

I will overview our results in sensing with one- and two-dimensional periodic arrays of nanostructured elements. To improve sensitivity, we employed nonlocal resonances featured by guided-mode resonances or bound-state-in the continuum modes. We proposed two novel modifications of one-dimensional high-contrast gratings regarding either better index contrast or improved access of the analytes to the hot spots of the local fields. Fabrication of the devices is done by deep-UV lithography, optimized etching and atomic layer deposition with conventional materials: silicon, alumina, titania and BCB polymer. Characterization of the sensors reveals improved sensing parameters, consistent with requirements for modern clinical diagnostic applications.

Partha BANERJEE

Maxwell to the rescue: metastructures and holography

In this talk I present two areas of personal interest developed at our Holography and Metamaterials Lab. First is the design of metallo-dielectric filters based on the underlying topological dispersion relation developed for TM and TE polarizations, heuristically modified to include material dispersion. The second is the use of transport of intensity and phase, derived from the Helmholtz equation, as an effective means of phase retrieval from holograms without the need for phase unwrapping.

Tom MACKAY, Akhlesh LAKHTAKIA

Oddly shaped inclusions: depolarization dyadics and homogenization

Closed-form expressions for depolarization dyadics were developed for truncated spheres and truncated spheroids, and the formalism was extended to truncated ellipsoids; the evaluation of depolarization dyadics for this latter case requires numerical integration. The Hölder continuity condition was exploited to fix the origin of the coordinate system for the evaluation of these depolarization dyadics. These results were used to develop an implementation of the Maxwell Garnett homogenization formalism for the relative permittivity parameters of homogenized composite mediums arising from an isotropic host medium impregnated with isotropic inclusions that are truncated spheres, spheroids, and ellipsoids.

John SCHOTLAND

A PDE Perspective on Many-body Problems in Quantum Optics

Quantum optics is the quantum theory of the interaction of light and matter. In this talk, I will describe a real-space formulation of quantum electrodynamics. The goal is to understand the propagation of nonclassical states of light in systems consisting of many atoms. In this setting, there is a close relation to kinetic equations for nonlocal PDEs with random coefficients.

Guy A. E. VANDENBOSCH, Xuezhi ZHENG, and Christos MYSTILIDIS

Bridging the Computational Gap between Classic Electrodynamics and Quantum Physics

This talk will focus on the nonclassical effects in metallic nanoantennas with deep-nanometric features and report the latest progress on the new algorithms in Computational Electromagnetics (CEM) that can model the mesoscopic electrodynamics at the deep-nanometric scale. In the talk, we will start with answering the very key question, that is, “under which circumstances do we need to consider the nonclassical effects in metallic nanoantennas?” Then, we briefly discuss the underlying mesoscopic physics and especially emphasize two nonclassical models: (1) the nonlocal hydrodynamic Drude model and (2) the surface response model. Further, we show how these two nonclassical models can be integrated with the T-matrix and the Boundary Element Method (BEM). Not only the work done in my group but also the results from the whole community are reviewed. Lastly, we demonstrate the application of the developed algorithms to real-life structures and give an overview of possible future research.

Igor SMOLYANINOV (remote)

Surface electromagnetic waves in lossy conductive media

A theory of surface electromagnetic waves in gradient media exhibiting arbitrary surface gradients of dielectric permittivity and magnetic permeability has been developed. Novel low-loss propagating surface wave solutions have been found in the gradient media in which both dielectric permittivity and magnetic permeability are dominated by their imaginary parts. Several examples of gradient geometries in which the surface wave problem may be solved analytically have been found. Experimental observations of these novel surface waves will be discussed. Examples of practically useful surface wave geometries spanning from radio communication underwater to UV nanophotonics have been demonstrated.

Gérard GOUESBET

Two curiosities in light scattering and light propagation: the failure of the optical theorem, and the speed of laser light in vacuum smaller than the speed of light

The description of laser beams for implementation in light scattering theories may rely on the use of two approaches (i) decompose on a set of basic functions and evaluate expansion coefficients or (ii) decompose over a set of plane waves [1]. While the second approach is inefficient when it has to be handle numerically, it is conceptually efficient to demonstrate two important properties in light scattering and propagation, namely (i) the optical theorem is not valid under structured beam illumination, a property which is valid as well in acoustics and quantum mechanics [2] (ii) the speed of laser light, even in vacuum, is smaller than the speed of light and may even, in principle, be made arbitrary small [3].
[1] G. Gouesbet and G.Gréhan. Generalized Lorenz-Mie theories, 3rd edition. Springer, 2023.
[2] G. Gouesbet and P.L. Marston. Failures of the classical optical theorem under arbitrary-shaped beam incidence in electromagnetism, acoustics, and quantum mechanics: motivation and a review. Frontiers in Physics, (10.3389/fphy.2023.1271555), 2023.
[3] G. Gouesbet and J.A. Lock. Consequences of the angular spectrum decomposition of a focused beam including slower than c beam propagation. Journal of Quantitative Spectroscopy and Radiative Transfer, 178:142-151, 2016.

Theo RASING

Optical control of magnetism thru strongly non-equilibrium phases

Since our demonstration of magnetization reversal by a single 40 femtosecond laser pulse, the manipulation of spins by ultra-short laser pulses has developed into an alternative and energy efficient approach to magnetic recording. Though originally thought to be due to an optically induced effective field, later studies demonstrated that the switching occurred via a strongly non-equilibrium state, exploiting the exchange interaction between the spins. Recent work also shows how magnetic textures like skyrmions are generated via a non-equilibrium phase. While for a long time, all-optical switching (AOS) was exclusively observed in ferrimagnetic alloys, more recent work demonstrated AOS in a broad range of ferromagnetic multilayer materials, though here a large number of pulses were required. By studying the dynamics of this switching process, we have discovered that this switching is a 2-step process, which led us to the subsequent demonstration that highly efficient AOS can be achieved by using pairs of femto/pico-second laser pulses. Combining optical laser excitation with in-situ magnetic force microscopy we recently found that the nucleation and switching process evolves via a stochastic network of domains, but a detailed understanding is still missing.
Acknowledgement(s): Support from the Dutch Research Council (NWO) and the European Research Council ERC grant agreement no.856538 (3D-MAGiC) is acknowledged.

Gerhard KRISTENSSON

Sum rules and physical bounds for a particulate slab

In recent years, many useful sum rules and physical bounds have been developed for electromagnetic applications such as radar absorbers, periodic structures (frequency selective surfaces), passive scatterers, antennas, metamaterials, near-zero material, and high impedance surfaces. In this paper, two different sum rules for transmission of the coherent (average) electromagnetic field by a particulate slab are established. These sum rules are obtained assuming the particles are passive scatterers and satisfy energy conservation and causality conditions. The sum rules are then employed to generate physical bounds on a combination of the bandwidth and a given transmission level. The exact sum rule has also a potential to verify the numerical implementation of the calculation of the transmission coefficient.

Nikolaos TSITSAS

Modeling of Electromagnetic Scattering by Cylindrical Arrays with the Method of Auxiliary Sources and Applications in EMC/EMI

Modeling of Electromagnetic Scattering by Cylindrical Arrays with the Method of Arrays of perfectly conducting, dielectric or core-shell cylinders exhibit under certain conditions in a specific frequency range either an effective negative permittivity (ENG) or an effective negative permeability (MNG) or a double negative (DNG) behavior. For this reason, such cylindrical arrays have been traditionally employed as key components of metamaterials. In this work, we investigate the shielding effectiveness of ENG cylindrical arrays consisting of perfect electric conducting (PEC), dielectric BST, core-shell PEC-BST, and graphene coated cylinders. Efficient variants of the Method of Auxiliary Sources (MAS) have been developed for the numerical modeling of the considered arrays. It is demonstrated that significantly high values of the shielding effectiveness can be obtained.

Martin W. McCALL, Stefanos Fr. KOUFIDIS

Recent advances in the theory of scattering from Bragg gratings

We discuss recent advances in the theory of Bragg scattering from gratings, including:
1) the use of Mobius transformations that reduce the description of Bragg scattering to a single ODE in a real variable, including structurally chiral media.
2) Hybrid media exhibiting both structural and molecular chirality, wherein a novel 'reverse Bragg' phenomenon is demonstrated.
3) Bragg-like reflection from a homogeneous medium, illustrating a recently discovered novel circular Bragg phenomenon.
4) Scattering from temporal gratings, both from simple isotropic media, through to media described by complex Tellegen constitutive relations.

Carsten ROCKSTUHL

Scattering theory in spatially structured time-varying media

We present a theory and numerical framework for analyzing light in spatiotemporal metamaterials. These metamaterials consist of spatially structured media made from time-varying materials. They leverage the dynamic properties of materials to manipulate light in unprecedented ways, including momentum band gaps and parametric amplification. By starting with eigenmodes in uniform, time-varying media, we introduce a scattering theory for light interaction with time-varying spheres and extend this to explore the optical responses of 2D and 3D periodic structures. Our framework addresses the characteristics of spatiotemporal metasurfaces and metamaterials, emphasizing the exploitation of structural resonances to enhance phenomena inherent to time-varying materials.

Didier FELBACQ

Characterizing the topological properties of one-dimensional nonhermitian systems without the Berry-Zak phase

A new method is proposed to predict the topological properties of one-dimensional periodic structures in wave physics, including quantum mechanics. From Bloch waves, a unique complex valued function is constructed, exhibiting poles and zeros. The sequence of poles and zeros of this function is a topological invariant that can be linked to the Berry-Zak phase. Since the characterization of the topological properties is done in the complex plane, it can easily be extended to the case of non-hermitian systems. The sequence of poles and zeros allows to predict topological phase transitions.

Peter MONK

Trefftz numerical methods for Maxwell's equation

Trefftz methods use a linear combination of exact solutions of Maxwell’s equations to approximate the overall solution. Combining this approach with the Discontinuous Galerkin Method on a finite element grid gives a Trefftz Discontinuous Galerkin method (T-DG). In this presentation I will derive a class of such methods. Then, after a discussion of convergence theory, I will present examples showing how the method works on standard examples, finishing with scattering from an aircraft at X-band frequencies. Drawbacks of this type of method, and open problems will also be presented.

Philippe BEN-ABDALLAH

Near-field heat transfer close to the contact and in non-reciprocal many-body systems

In the first part of this presentation, I will describe the physics which drives the near-field radiative heat transfer between two polar materials close to the contact [1]. I will show that the acoustic vibrations modes play a major role in the non-local optical response of materials, and I will highlight its dominant role in the heat transfer at cryogenic temperatures. The second part will be devoted to near-field radiative heat exchanges in magneto-optical many-body systems [2]. I will show that the time reversal symmetry breaking of Maxwell’s equation gives rise to a class of peculiar effects [3-5].
References
[1] M. Gómez Viloria, Y. Guo, S. Merabia, R. Messina, and P. Ben-Abdallah, Phys. Rev. B 108, L201402 (2023).
[2] S.A. Biehs, R. Messina, P.S. Venkataram, A.W. Rodriguez, J.C. Cuevas, and P. Ben-Abdallah, Rev. Mod. Phys. 93, 025009 (2021).
[3] L. Zhu and S. Fan, Phys. Rev. Lett. 117, 134303 (2016).
[4] I. Latella and P. Ben-Abdallah, Phys. Rev. Lett. 118, 173902 (2017).
[5] P. Ben-Abdallah, Phys. Rev. Lett. 116, 084301 (2016).

Akhlesh LAKHTAKIA

Geometric phase and Reusch piles

The geometric phase has acquired interest for optical devices such as achromatic phase shifters, spatial light modulators, frequency shifters, and planar lenses for wavefront engineering. Nanoarchitected materials are expected to open many avenues for geometric-phase engineering. I will discuss my initial foray into this arena through Reusch piles, the concept of which can be enlarged to encompass columnar, chevronic, ambichiral, equichiral, and finely chiral thin films.