Brahim Guizal

• Ph.D. Sc. D.
• Professor (Full) at Université de Montpellier

The design of metallic contact grids on the front side of thermophotovoltaic cells is critical since it can cause significant optical and electrical resistive losses, particularly in the near field. However, from the theoretical point of view, this effect has been either discarded or studied by means of extremely simplified models like the shadowin...

We study the normal and lateral components of the Casimir-Lifshitz (CL) force between a nanoparticle and 1D graphene grating deposited on a fused silica slab. For this purpose, the scattering matrix approach together with the Fourier modal method augmented with local basis functions are used. We find that, by covering a fused silica slab by a graph...

We investigate the near-field radiative heat transfer between a normally and/or laterally shifted nanoparticle and a planar fused silica slab coated with a strip graphene grating. For this study, we develop and use a scattering matrix approach derived from Fourier modal method augmented with local basis functions. We find that adding a graphene she...

We study the Casimir-Lifshitz force (CLF) between a gold plate and a graphene-covered dielectric grating. Using a scattering matrix (S-matrix) approach derived from the Fourier modal method (FMM), we find a significant enhancement in the CLF as compared to a mere dielectric slab coated with graphene, over a wide range of temperatures. Additionally,...

We investigate the near-field radiative heat transfer between a normally and/or laterally shifted nanoparticle and a planar fused silica slab coated with a strip graphene grating. For this study we develop and use a scattering matrix approach derived from Fourier modal method augmented with local basis functions. We find that adding a graphene shee...

We examine the near-field radiative heat transfer between finite-thickness planar fused silica slabs covered with graphene gratings, through the utilization of the Fourier modal method augmented with local basis functions (FMM-LBF), with a focus on the lateral shift effect (LSE). To do so, we propose and validate a minor modification of the FMM-LBF...

We study the Casimir-Lifshitz force (CLF) between a gold plate and a graphene-covered dielectric grating. Using a scattering matrix (S-matrix) approach derived from the Fourier Modal Method (FMM), we find a significant enhancement in the CLF as compared to a mere dielectric slab coated with graphene, over a wide range of temperatures. Additionally,...

In this work, we analyze the near-field radiative heat transfer (NFRHT) between finite-thickness planar fused silica slabs coated with graphene gratings. We go beyond the effective medium approximation by using an exact Fourier modal method equipped with specific local basis functions, and this is needed for realistic experimental analysis. In gene...

We study the nonequilibrium Casimir-Lifshitz force between graphene-based parallel structures held at different temperatures and in the presence of an external thermal bath at a third temperature. The graphene conductivity, which is itself a function of temperature, as well as of chemical potential, allows us to tune in situ the Casimir-Lifshitz fo...

We investigate the Casimir-Lifshitz force (CLF) between two identical graphene strip gratings, laid on finite dielectric substrate. By using the scattering matrix (S-matrix) approach derived from the Fourier Modal Method with local basis functions (FMM-LBF), we fully take into account the high-order electromagnetic diffractions, the multiple scatte...

We study the non equilibrium Casimir-Lifshitz force between graphene-based parallel structures held at different temperatures and in presence of an external thermal bath at a third temperature. The graphene conductivity, which is itself a function of temperature, as well as of chemical potential, allows us to tune in situ the Casimir-Lifshitz force...

We present a numerical approach for the solution of electromagnetic scattering from a dielectric cylinder partially covered with graphene. It is based on a classical Fourier-Bessel expansion of the fields inside and outside the cylinder to which we apply ad hoc boundary conditions in the presence of graphene. Due to the singular nature of the elect...

We present a numerical approach for the solution of electromagnetic scattering from a dielectric cylinder partially covered with graphene. It is based on a classical Fourier-Bessel expansion of the fields inside and outside the cylinder to which we apply ad-hoc boundary conditions in presence of graphene. Due to the singular nature of the electric...

We propose a simple semi analytical model that allows to compute the transmittance and reflectance of a one dimensional subwavelength graphene strip grating under an external static magnetic field. In this model graphene is treated as an anisotropic layer with atomic thickness and a frequency dependent complex permittivity tensor. The model is base...

We propose a simple semi analytical model that allows to compute the transmittance and reflectance of a one dimensional subwavelength graphene strip grating under an external static magnetic field. In this model graphene is treated as an anisotropic layer with atomic thickness and a frequency dependent complex permittivity tensor. The model is base...

We propose a simple semi analytical model that allows to compute the transmittance and reflectance of a one dimensional subwavelength graphene strip grating under an external static magnetic field. In this model graphene is treated as an anisotropic layer with atomic thickness and a frequency dependent complex permittivity tensor. The model is base...

The classical adjoint-based topology optimization (TO) method, based on the use of a random continuous dielectric function as an adjoint variable distribution, is known to be one of the most efficient optimization methods that enable the design of optical devices with outstanding performances. However, the strategy for selecting the optimal solutio...

Quantum fluctuations give rise to Casimir forces between two parallel conducting plates, the magnitude of which increases monotonically as the separation decreases. By introducing nanoscale gratings to the surfaces, recent advances have opened opportunities for controlling the Casimir force in complex geometries. Here, we measure the Casimir force...

In dense systems composed of numerous nanoparticles, direct simulations of near-field radiative heat transfer (NFRHT) require considerable computational resources. NFRHT for the simple one-dimensional nanoparticle chains embedded in a non-absorbing host medium is investigated from the point of view of the continuum by means of an approach combining...

We present a topology optimization method for a 1D dielectric metasurface, coupling the classical fluctuations-trend analysis (FTA) and diamond-square algorithm (DSA). In classical FTA, a couple of device distributions termed fluctuation or mother and trends or father, with specific spectra, is initially generated. The spectral properties of the tr...

We present a topology optimization (TO) method for a 1D dielectric metasurface, coupling the classical trend-fluctuations analysis (FTA) and the diamond-square-algorithm (DSA). In the classical FTA, a couple of device distributions termed Fluctuation or mother and Trends or father, with specific spectra is initially generated. The spectral properti...

Quantum fluctuations give rise to Casimir forces between two parallel conducting plates, the magnitude of which increases monotonically as the separation decreases. By introducing nanoscale gratings to the surfaces, recent advances have opened opportunities for controlling the Casimir force in complex geometries. Here, we measure the Casimir force...

In dense systems composed of numerous nanoparticles, direct simulations of near-field radiative heat transfer (NFRHT) require considerable computational resources. NFRHT for the simple one-dimensional nanoparticle chains embedded in a non-absorbing host medium is investigated from the point of view of the continuum by means an approach combining th...

We study the Casimir torque between two metallic one-dimensional gratings rotated by an angle θ with respect to each other. We find that, for infinitely extended gratings, the Casimir energy is anomalously discontinuous at θ=0, due to a critical zero-order geometric transition between a 2D- and a 1D-periodic system. This transition is a peculiarity...

Metasurfaces are planar metamaterials that consist of a single or a few stack of subwavelength thickness metal-dielectric layers. They could be periodically structured or not with subwavelength scale patterns according to the transverse directions. The strong interac- tion between an electromagnetic field components and these surfaces, exhibits som...

The polynomial modal method (PMM) is one of the most powerful methods for modeling diffraction from lamellar gratings. In the present work, we show that applying it to the so-called matched coordinates leads to important improvement of convergence for crossed lamellar gratings with patterns that are not parallel to the coordinates’ axes. After givi...

The radiative heat transfer between two dielectrics can be strongly enhanced in the near field in the presence of surface phonon-polariton resonances. Nevertheless, the spectral mismatch between the surface modes supported by two dissimilar materials is responsible for a dramatic reduction of the radiative heat flux they exchange. In the present pa...

We show that graphene-dielectric multilayers give rise to an unusual tunability of the Casimir-Lifshitz forces, and allow to easily realize completely different regimes within the same structure. Concerning thermal effects, graphene-dielectric multilayers take advantage from the anomalous features predicted for isolated suspended graphene sheets, e...

We calculate the radiative heat transfer between two identical metallic one-dimensional lamellar gratings. To this aim we present and exploit a modification to the widely-used Fourier modal method, known as adaptive spatial resolution, based on a stretch of the coordinate associated to the periodicity of the grating. We first show that this techniq...

We calculate the radiative heat transfer between two identical metallic one-dimensional lamellar gratings. To this aim we present and exploit a modification to the widely-used Fourier modal method, known as adaptive spatial resolution, based on a stretch of the coordinate associated to the periodicity of the grating. We first show that this techniq...

We present a numerical approach for the solution of the dissipative Gross-Pitaevskii equation coupled to the reservoir equation governing the exciton-polaritons Bose-Einstein condensation. It is based on the finite difference method applied to space variables and on the fourth order Range-Kutta algorithm applied to the time variable. Numerical test...

The purpose of this chapter is to present a unified theory for the numerical implementation of modal methods for the analysis of electromagnetic phenomena with specific boundary conditions. All the fundamental concepts that form the basis of our study will be detailed. In plasmonics and photonics in general, solving Maxwell equations involving irre...

Abstract- Behind the appellation “modal methods”, for diffraction gratings, one can find a variety of methods sharing in common the development of the fields in terms of basis functions that can be either Fourier exponentials hence the name Fourier Modal Method (FMM), or polynomials leading to the family of Polynomial Modal Methods (Legendre, Tcheb...

Heat flux exchanged between two hot bodies at subwavelength separation distances can exceed the limit predicted by the blackbody theory. However this super-Planckian transfer is restricted to these separation distances. Here we demonstrate the possible existence of a super-Planckian transfer at arbitrary large separation distances if the interactin...

Heat flux exchanged between two hot bodies at subwavelength separation distances can exceed the limit predicted by the blackbody theory. However this super-Planckian transfer is restricted to these separation distances. Here we demonstrate the possible existence of a super-Planckian transfer at arbitrary large separation distances if the interactin...

We propose a model taking into account the periodic spatial modulation of a doped graphene sheet conductivity when it is placed in the vicinity of a dielectric grating. We then compute the absorption and study the excitation of surface plasmons on such a structure. We show that it is possible to excite surface modes leading to very high absorption....

We show that the electromagnetic forces generated by the excitations of a mode in graphene-based optomechanical systems are highly tunable by varying the graphene chemical potential, and orders of magnitude stronger than usual non-graphene-based devices, in both attractive and repulsive regimes. We analyze coupled waveguides made of two parallel gr...

We derive the explicit expression for the Casimir energy between a sphere and a 1D grating, in terms of the sphere and grating reflection matrices, and valid for arbitrary materials, sphere radius, and grating geometric parameters. We then numerically calculate the Casimir energy between a metallic (gold) sphere and a dielectric (fused silica) lame...

The strong coupling between surface plasmons polaritons (SPP) of a doped graphene sheet and those of a Metal/Dielectric/Metal (MDM) like plasmonic waveguide is considered. It is shown that, under certain conditions, these different modes can be hybridized to give rise to new modes whose properties are strongly dependent on the geometrical features...

Thanks to its particular optical properties, graphene, a planar honeycomb lattice of carbon atoms, has attracted much attention in the last few years. Recently, it has been shown that this material, unlike metals, can support both TE (transverse electric) and TM (transverse magnetic) surface plasmons but yet a simple method of exciting such modes i...

Optical properties of GaN/Al0.2Ga0.8N multiple quantum wells grown with semi-polar (10-11) orientation on patterned 7°-off Si (001) substrates have been investigated. Studies performed at 8 K reveal the in-plane anisotropic behavior of the QW photoluminescence (PL) intensity for this semi-polar orientation. The time resolved PL measurements were ca...

We calculate the Casimir-Lifshitz pressure in a system consisting of two different 1D dielectric lamellar gratings having two different temperatures and immersed in an environment having a third temperature. The calculation of the pressure is based on the knowledge of the scattering operators, deduced using the Fourier Modal Method. The behavior of...

The optical properties of GaN/Al0.15Ga0.85N multiple quantum wells are examined in 8 K–300 K temperature range. Both polarized CW and time resolved temperature-dependent photoluminescence experiment are performed so that we can deduce the relative contributions of the non-radiative and radiative recombination processes. From the calculation of the...

A layered waveguide supported hybrid modes between a surface plasmon and a confined guided mode is studied. The condition for the strong coupling regime are described. The Green function is obtained and decomposed along the continuous and discrete spectrum.

The effect of confinement on surface plasmon polariton in a planar nanocavity was studied. The generalized modes were obtained and studied in detail. In this work, we study the effect of confinement on surface plasmons in a planar cavity with a wall coated with a lossy metal as well as with two walls coated with a lossy metal. The dispersion curves...

Surface Plasmons (SP) are electromagnetic modes that do exist at the interface between a dielectric and a metal. For metallic particles (spheres, ellipsoids...), such modes are termed localized surface plasmons (LSP). They are at origin of the red colour of Au colloidal solutions and that of the famous Lycurgus cup (Roman glass cup now in the Briti...

In this paper we present an extension of the modal method by Gegenbauer expansion (MMGE) [J. Opt. Soc. Am. A 28, 2006 (2011)], [Progress Electromagn. Res. 133, 17 (2013)] to the study of nonperiodic problems. The nonperiodicity is introduced through the perfectly matched layers (PMLs) concept, which can be introduced in an equivalent way either by...

The Modal Method by Gegenbauer polynomials Expansion (MMGE) has been recently introduced for lamellar gratings by Edee [8]. This method shows a promising potential of outstanding convergence but still suffers from instabilities when the number of polynomials is increased. In this work, we identify the origin of these instabilities and propose a way...

It is shown that it is possible to realize strong coupling between a surface plasmon and a guided mode in a layered structure. The dispersion relation of such a structure is obtained through the S-matrix algorithm combined with the Cauchy integral technique that allows for rigorous computations of complex poles. The strong coupling is demonstrated...

We employ a time-domain method to compute the near field on a contour enclosing infinitely long cylinders of arbitrary cross section and constitution. We therefore recover the cylindrical Hankel coefficients of the expansion of the field outside the circumscribed circle of the structure. The recovered coefficients enable the wideband analysis of co...

A metal-dielectric - waveguide layered structure is considered. It is shown that the regime of weak and strong coupling between the modes confined in the dielectric waveguide and the surface plasmon can be obtained. The strong coupling allows the spatial exchange of energy and opens a way towards the quantum control of plasmon, i.e. quantum plasmon...

Light transport in two-dimensional disordered metamaterials made of high-permittivity rods is studied theoretically. Different regimes of transport are observed and explained in terms of coupled electric and magnetic dipolar resonances. A very general homogenization theory is derived. Light propagation at frequencies close to the magnetic dipole re...

We, theoretically, show that it is possible to realize the strong coupling of a guided mode with a surface plasmon in a waveguide coated by a lossy metal. The dispersion relation of such a structure is obtained through the T-matrix algorithm combined with the the Cauchy integral technic that allows for rigorous computations of the complex poles. Th...

We have computed the excitonic states in the case of cylindrical symmetry as a function of the anisotropy using the finite-element method. The wave functions are also obtained and are presented for m = 0, the states coupled with the electromagnetic fields. We illustrate for instance that the state dominantly built from the 3d0 hydrogenic level has...

The strong coupling between a mode confined in a dielectric waveguide and a surface plasmon was demonstrated. It was shown that the strong and weak coupling regime can coexist. The strong coupling allows the spatial exchange of energy and opens a way towards the quantum control of plasmon, i.e. quantum plasmonics.

On montre l'existence de résonances électrostatiques dans le comportement basse fréquence de réseaux bidimensionnels métalliques.

The homogeneous and transport properties of a set of metallic fibers were studied. The existence of a plasma frequency was deduced and a precise formula for it was derived. A homogenized system for finite length ohmic wires was derived. Some numerical simulations were made to study the influence of disorder. The persistence of a low-frequency band...

We address the interpretation of the splitting between the ground state excitonic transition which indicates the energy of the lowest direct band gap in AlN bulk films and epilayers, and a 36-38 meV higher energy companion. We demonstrate that this splitting is consistent with the initial interpretation in terms of 1s-2s excitonic splitting by usin...

We review strain effects on excitonic energies in AlN

In this paper we propose an efficient technique for micromachining lithium niobate that is used in Ti-diffused waveguides. The use of Focused Ion Beam (FIB) etching allows obtaining homogeneous periodic microstructures. Bragg gratings with a period of 1.05 μm and an aspect ratio of 6:1 (depth-to-half period ratio) have been achieved. A reflectivity...

We address the computation of excitonic energies in the context of anisotropic dispersio relations and dielectric constant

The recent interest in the imaging possibilities of photonic crystals (superlensing, superprism, optical mirages, etc.) call for a detailed analysis of beam propagation inside a finite periodic structure. An answer to the following question was sought: "Where does the beam emerge?" We found that, contrary to common knowledge, it is not always true...

La formulation paramétrique de la méthode des conditions aux limites combinées (MCLC) équipée d’une résolution spatiale adaptative est étendue aux structures multicouches de réseaux de bandes métalliques extremement conductrices ”strips” en utilisant une nouvelle méthode pour résoudre le problème aux valeurs propres pour toutes les couches à la foi...

The parametric formulation of the Combined Boundary conditions Method (CBCM) with spatial adaptive resolution is extended to multilayered structures of strip gratings using a new method to solve the eigenvalue problem in all the layers.

The parametric formulation of the combined boundary conditions method (CBCM) with spatial adaptive resolution is extended to multilayered structures of strip gratings. Furthermore, it is shown that it is not necessary to solve the eigenvalue problem in all the layers of these structures; leading to drastic reduction of the computational load.

In its conventional form, the Transmission Line Modeling method is not capable of accounting for media whose constitutive parameters are exotic. Permittivity and permeability less than unity can be reached by using a mesh that is the numerical counterpart of a dispersive left-handed transmission line network. In this communication, the dispersion t...

In our sample, the spectral field of the electromagnetic waves terahertz, surface plasmon polaritons (SPPs) have a long propagation length at a metallic strip grating surface [1]. This property allows imagining two-dimensional wave guides at the surface in the terahertz domain. The excitation of these surface plasmons with an incidental wave can be...

A numerical improvement of the Fourier modal method with adaptive spatial resolution is obtained. It is shown that the solutions of all the eigenvalue problems corresponding to homogeneous regions can be deduced straightforwardly from the solution of one of these problems. Numerical examples demonstrate that computation time saving can be substanti...

We investigate numerically and theoretically the homogeneous properties of a metamaterial made of nanorods with a high dielectric constant. The rods have inner resonances leading to an effective magnetic behavior. The influence of various parameters, such as the wavelength, the angle of incidence, and the filling ratio is quantified by means of rig...

The Fourier modal method equipped with the concept of adaptive spatial resolution (FMMASR) is shown to be naturally more stable than the classical Fourier modal method toward spurious modes that appear with metallic structures. It is demonstrated that this stability can be further improved by reformulating the eigenvalue problem of the FMMASR.

The effective electromagnetic properties of a metamaterial made of nanorods are investigated. It is found that near inner resonances there is a effective magnetic behavior. The domain of validity of the effective permeability model is determined with respect to the wavelength and the filling ratio by means of rigorous numerical computations. It is...

In this work we study the diffraction of electromagnetic waves for an aperiodic strip structure such us finite strip gratings, a single strip or a single slit. The fields are, first, writen in terms of th so-called Rayleigh expansion above and below the strips.

The homogeneous and transport properties of a set of metallic fibers was studied. The existence of a plasma frequency was shown and a precise formula was derived. A homogenized system for finite length ohmic wires was derived. Some numerical simulations were made to study the influence of disorder.

Light propagation in all-dielectric rod-type metamaterials is studied theoretically. The electric and magnetic dipole moments of the rods are derived analytically in the long-wavelength limit. The effective permittivity and permeability of a square lattice of rods are calculated by homogenizing the corresponding array of dipoles. The role of dipole...

It was recently established that coaxial nano-aperture arrays perforated in optically thick silver films exhibit an extraordinary transmission in the visible range thanks to a guided mode. However this mode has a cut-off wavelength beyond which the transmission dramatically decreases. We propose here a cascaded structure that is shown to act as a h...

Wave propagation in thin nanostructured films in the low frequency regime was studied. By means of a two-scale analysis, the medium can be homogenized, i.e. described by effective electromagnetic parameters. The effective permeability and permittivity were obtained from a set of partial differential equations. A numerical approach based on the Four...

We report second harmonic generation (SHG) measurements in reflectivity from chains of gold nanoparticles interconnected with metallic bridges. We measured more than 30 times a SHG enhancement when a surface plasmon resonance was excited in the chains of nanoparticles, which was influenced by coupling due to the electrical connectivity of the bridg...

Wave propagation in thin nanostructured films in the low frequency regime is studied. By means of a two-scale analysis, it is shown that the medium can be homogenized, i.e. described by effective electromagnetic parameters. The effective permeability and permittivity are obtained by solving a set of partial differential equations. A numerical aproa...

On démontre l'existence d'une forte densité d'états autorisant le passage de la lumière dans des structures de piliers diélectriques.

Light propagation in all-dielectric rod-type metamaterials is studied theoretically. The electric and magnetic dipole moments of the rods are derived analytically in the long-wavelength limit. The effective permittivity and permeability of a square lattice of rods are calculated by homogenizing the corresponding array of dipoles. The role of dipole...

The direction of propagation followed by a monochromatic beam in a periodic structure is generally deduced from the isofrequency diagram, which is related to the group velocity. However, the group velocity is the derivative of ω with respect to the wavenumber, while the behavior of the beam should depend on ω only. In the subwavelength regime, a me...

The determination of the reflection and transmission coefficients of the multi-layer structure rests on the formalism of the matrices of transfer using the differential equations deduced from the Maxwell's equations. It is shown that a judicious choice of the refraction indexes, optical thicknesses of the various layers and number of periods makes...

The C method is known to be one of the most efficient and versatile tools established for modeling diffraction gratings. Its main advantage is the use of a coordinate system in which the boundary conditions apply naturally and are, ipso facto, greatly simplified. In the context of scattering from random rough surfaces, we propose an extension of th...

The recent interest in the imaging possibilities of photonic crystals (superlensing, superprism, optical mirages etc...) call for a detailed analysis of beam propagation inside a finite periodic structure. In this paper, an answer to the question "where does the beam emerge?" is given. Contrarily to common knowledge, it is not always true that the...

Wave propagation and diffraction in a membrane photonic crystal with finite height were studied in the case where the free-space wavelength is large with respect to the period of the structure. The photonic crystals studied are made of materials with anisotropic permittivity and permeability. Use of the concept of two-scale convergence allowed the...

The numerical study of the acoustic (elastic) effect in periodically nanostructured metallic films exhibiting extraordinary optical transmission (EOT) deposited onto the top of a piezoelectric material is reported. Surface acoustic waves are generated in the piezoelectric substrate and their influence in the transmission spectrum of the EOT structu...

We present a comparison among several fully-vectorial methods applied to a basic scattering problem governed by the physics of the electromagnetic interaction between subwavelength apertures in a metal film. The modelled structure represents a slit-groove scattering problem in a silver film deposited on a glass substrate. The benchmarked methods, a...

A cascaded structure of annular aperture arrays perforated in silver films is shown to act as a high quality Fabry-Pérot interferometer (quality factor up to 200). The transmission of a single nanostructured layer exhibits a cut-off wavelength beyond which there is no transmission. It is demonstrated, here, that the double structure permits to over...