arXiv subjects

Philippe Lalanne

Publications and source records attributed to Philippe Lalanne.

At least 19 recordsLinked to original sources

arXiv2026

Expanding RCWA capabilities with advanced S-matrix algorithms

Modal methods are particularly well suited to layered photonic structures because electromagnetic propagation within each layer is described analytically. Here, we introduce a simple reformulation of the scattering-matrix (S-matrix) approach in which the S-matrix is defined as an intrinsic property of an individual layer, independently of its neighboring interfaces. This separation between layer propagation and interface coupling preserves the numerical stability of the conventional S-matrix formalism while providing a more modular description of multilayer structures. It also enables direct computation of the scattering coefficients between external plane waves and Bloch modes, as well as between Bloch modes themselves, providing generalized Fresnel coefficients for periodic interfaces. In addition, the reformulation allows the optical response to be evaluated simultaneously for many layer thicknesses or incident wavevectors, with only a modest computational overhead compared with a single calculation. Implemented in the RETICOLO freeware, these capabilities provide a practical framework for modal analysis, parameter sweeps, and the design of layered photonic structures.

physics.optics↗

arXiv2026

Revealing Sharp Spectral Features with Complex Frequency Excitations: Challenges and Opportunities

Broadening of spectral and spatial responses due to intrinsic loss in real materials often hides sharp features. One recently recognized route to recover those features is to probe the system with complex-frequency (CF) signals that decay exponentially in time: a suitably tailored temporal decay can compensate for loss and reveal an intrinsic, narrow response. However, generating rapidly decaying optical waveforms in real time is often challenging (the required decay times may be in the range of tens of femtoseconds). A recently proposed alternative synthesizes the CF response numerically after detection of conventional, real-frequency signals using Fourier post-processing. Here we explore advantages and challenges of these approaches: we show that a physical CF excitation robustly sharpens spectral features in the presence of noise, while a post-detection synthesized CF response shows only limited improvement once realistic detection and readout noise is considered. At the same time, in low-noise conditions a much simpler post-detection filtering procedure attains equal or better recovery than the synthesized CF reconstruction, making the synthesis unnecessary in practice.

physics.optics↗

arXiv2026

Rigorous electromagnetic quasinormal-mode method made easy for users

Full-wave numerical methods based on quasinormal modes (QNMs) offer valuable physical insights and computational efficiency for analyzing electromagnetic resonators. However, despite their advantages, many researchers in electromagnetism continue to favor real-frequency domain or time-domain approaches, often using finite element or finite-difference time-domain methods. This preference stems from various factors, including the perception that QNM theory is still developing or requires advanced mathematical tools from complex analysis. In this work, we combine numerical techniques with accurate ap-proximations to simplify the computation of QNMs and enable ultrafast reconstructions us-ing QNM expansions. The result is a new approach that is straightforwardly accessible to users familiar with real-frequency methods. We demonstrate the practicality of our ap-proach through an open-source package [Doi: 10.5281/zenodo.18708748] implemented within a widely-used commercial photonics software.

physics.optics↗

arXiv2026

Extrinsic Limitations of Stealthy Hyperuniform devices

Hyperuniformity promises an unusual form of wave control: the suppression of elastic scattering over extended angular ranges without periodic order. Here, we present a comprehensive experimental and theoretical study of 2D stealthy hyperuniform metasurfaces operating at optical frequencies. In agreement with theoretical expectations, we observe a pronounced reduction of elastic scattering around the specular direction in metasurfaces fabricated by electron-beam lithography. However, the measured suppression is substantially weaker than that predicted by structure-factor calculations based on ideal stealthy hyperuniform point-pattern generators. We identify and quantitatively analyze the physical origins of this discrepancy and establish realistic performance bounds. By isolating the dominant limiting mechanisms, our results provide practical design guidelines for the implementation of stealthy hyperuniformity in functional devices.

physics.optics↗

arXiv2025

Theory of superlensing with complex frequency illuminations

Recent experiments have demonstrated that the resolution of superlensing slabs can be significantly enhanced with complex frequency illuminations. In this study, we introduce a novel theoretical framework for analyzing superlensing. The framework offers new and transparent insights. It helps clarify what resolution can be expected with complex frequency, or more generally pulse illuminations, but it also highlights inherent limitations and tempers high expectations raised by the recent electromagnetic experiments. [accepted Optica]

physics.optics↗

arXiv2025

Dissipative Coupling in Photonic and Plasmonic Resonators

The rapid progress of nanophotonics demands theoretical frameworks capable of predicting the resonant behavior of complex systems comprising constituents of varying nature, operating beyond the weak-coupling, high-Q regime where classical temporal coupled-mode theory (CMT) is applicable. This work presents a coupled-quasinormal-mode (cQNM) framework for analyzing dissipative coupling with photonic and plasmonic resonators. The framework provides rigorous closed-form expressions for dissipative coupling coefficients and introduces novel features, such as a new coupling scheme via time derivatives of excitation coefficients. It delivers transparent and accurate predictions of exotic phenomena-such as zero-coupling between very close cavities and level-attraction effects that are only vaguely captured by traditional CMT models. Efficient and user-friendly, this framework facilitates rapid parameter space exploration for device design and offers potential for extension to nonlinear and quantum systems in future applications.

physics.optics↗

arXiv2025

Assembling and Modeling Stacked Disordered Metasurfaces

Disordered metasurfaces offer unique properties unattainable with periodic or ordered metasurfaces, notably the absence of deterministic interference effects at specific wavelengths and angles. In this work, we introduce a lithography-free nanofabrication approach to realize cascaded disordered plasmonic metasurfaces with sub-micron total thickness. We experimentally characterize their angle-resolved specular and diffuse reflections using the bidirectional reflection distribution function (BRDF) and develop accurate theoretical models that remain valid even at large incidence angles. These models reveal the intricate interplay between coherent (specular) and incoherent (diffuse) scattering and demonstrate how coherent illumination can strongly influence the perceived color of diffusely scattered light. Exploiting this effect, we realize a centimeter-scale chromo-encryption device whose color changes depending on whether it is viewed under direct or diffuse illumination. Our results lay the groundwork for advanced nanophotonic platforms based on stacked disordered metasurfaces, offering versatile optical functionalities inaccessible with traditional multilayer thin-film technologies or single-layer metasurfaces.

physics.optics↗

arXiv2025

Emergent scattering regimes in disordered metasurfaces near critical packing

Disordered metasurfaces provide a versatile platform for harnessing near- and far-field scattered light. Most research has focused on either particulate topologies composed of individual, well-identified metaatoms or, to a lesser extent, semi-continuous aggregate topologies without well identified inclusions. Here, we uncover an intermediate critical packing regime characterized by metasurface morphologies in which a significant fraction of metaatoms begin to connect. We experimentally demonstrate that, at this threshold, the properties of the scattered light abruptly change and, via a statistical quasinormal mode analysis, interpret this change as a marked transition in the statistics of the photon density of states. Unlike percolation in semicontinuous metal films, this transition affects not only the specular but also the diffuse components of the scattered light in a profound way. Our results introduce critical packing topologies as a novel design strategy for manipulating the spectral and angular characteristics of light using ultrathin optical coatings. Emergent functionalities include colour shifts in diffuse light driven by multiple scattering and surface whitening, with potential applications in display technologies, for example, to reduce glare in electronic screens.

physics.optics↗

arXiv2025

RETICOLO software for grating analysis

RETICOLO is a freeware that implements the rigorous coupled wave analysis (RCWA) for 1D (classical and conical diffraction) and 2D crossed gratings. It operates under a MATLAB environment and incorporates an efficient and accurate toolbox for computing Bloch modes and visualizing the electromagnetic field in the grating region. As a spin-off, the Version V9 and the following ones include a toolbox for the analysis of stacks of arbitrarily anisotropic multilayered thin-films.

physics.optics↗

arXiv2024

Quasinormal mode as a foundational framework for all electromagnetic Fano resonances

Fano profiles are observed across various fields of wave physics. They emerge from interference phenomena and are quantified by the asymmetry parameter q. In optics, q is usually considered as a phenomenological coefficient obtained by fitting experimental or numerical data. In this work, we introduce an ab initio Maxwellian approach using quasinormal modes to analytically describe line shapes in light scattering problems. We show that the response of each individual quasinormal mode inherently exhibits a Fano profile and derive an explicit analytical formula for the Fano parameter. Experimental and numerical validations confirm the formula's accuracy across a broad spectrum of electromagnetic systems. The general expression for q opens new possibilities for fine-tuning and optimizing spectral line shapes in electromagnetism.

physics.optics↗

arXiv2024

On the Exact Maxwell evolution equation of resonator dynamics

In a recent publication [Opt. Express 32, 20904 (2024)], the accuracy of the main evolution equation that governs resonator dynamics in the coupled-mode theory (CMT) was questioned. The study concluded that the driving force is proportional to the temporal derivative of the excitation field rather than the excitation field itself. This conclusion was reached with a derivation of an "exact" Maxwell evolution (EME) equation obtained directly from Maxwell's equations, which was further supported by extensive numerical tests. Hereafter, we argue that the original derivation lacks mathematical rigor. We present a direct and rigorous derivation that establishes a solid mathematical foundation for the EME equation. This new approach clarifies the origin of the temporal derivative in the excitation term of CMT and elucidates the approximations present in the classical CMT evolution equation through a straightforward argument.

physics.optics↗

arXiv2024

Discussions on the spatial exponential growth of electromagnetic quasinormal modes

The temporal response of open systems is marked by damped oscillations. These oscillations, often referred to as ringings, are the signature of the decay of quasinormal modes (QNMs). A major research objective across various fields is to represent the response of open systems using QNM expansions, akin to the treatment of normal modes in closed systems. In electromagnetism, it is widely acknowledged that QNM expansions provide a relevant representation of the modal physics within the interior of compact resonators in free space, where QNMs form a complete set of the resonator. However, challenges emerge in the exterior of the resonator, where QNM fields exhibit exponential divergence, rendering QNM expansions incomplete. The divergence poses delicate mathematical issues that often lead to misinterpretations on the physics side. Hereafter, we analyze foundational concepts such as cavity perturbation theory and dissipative coupling between resonators. By studying model problems, we show that the exponential growth is physical and meaningful for understanding the interaction between remote electromagnetic bodies. The analysis consistently reveals that the coupling coefficients between QNMs of two distant bodies strengthen as the separation distance increases, therein challenging the intuition that distant bodies behave independently. These insights that shed light on the origin and implications of the divergence hold significant implications for understanding the ability of contemporary electromagnetic QNM theories in offering a modal representation of the physics in the open space surrounding resonator bodies. Our critical examination of these theories reveals the existence of two distinct perspectives and elucidates the significance of their contrasting viewpoints.

physics.optics↗

arXiv2024

Designing electromagnetic resonators with quasinormal modes

Micro- and nanoresonators, which enable light trapping in small volumes for extended durations, play a crucial role in modern photonics. The optical response of these resonators is determined by their fundamental resonances, known as quasinormal modes (QNMs). Over the past decade, the electromagnetic theory of QNMs has undergone significant development and has now reached a level of maturity that allows its reliable application to numerous contemporary electromagnetic problems. In this review, we explore recent applications of QNM theory for designing and understanding micro and nanoresonators. We highlight why QNMs provide deep physical insights and enhance computational efficiency in scenarios involving mode hybridization and perturbation.

physics.optics↗

arXiv2024

T-matrix representation of optical scattering response: Suggestion for a data format

The transition matrix, frequently abbreviated as T-matrix, contains the complete information in a linear approximation of how a spatially localized object scatters an incident field. The T-matrix is used to study the scattering response of an isolated object and describes the optical response of complex photonic materials made from ensembles of individual objects. T-matrices of certain common structures, potentially, have been repeatedly calculated all over the world again and again. This is not necessary and constitutes a major challenge for various reasons. First, the resources spent on their computation represent an unsustainable financial and ecological burden. Second, with the onset of machine learning, data is the gold of our era, and it should be freely available to everybody to address novel scientific challenges. Finally, the possibility of reproducing simulations could tremendously improve if the considered T-matrices could be shared. To address these challenges, we found it important to agree on a common data format for T-matrices and to enable their collection from different sources and distribution. This document aims to develop the specifications for storing T-matrices and associated metadata. The specifications should allow maximum freedom to accommodate as many use cases as possible without introducing any ambiguity in the stored data. The common format will assist in setting up a public database of T-matrices.

physics.optics↗

arXiv2024

Exact Maxwell evolution equation of resonators dynamics: temporal coupled-mode theory revisited

Despite its widespread significance, the temporal coupled-mode theory (CMT) lacks a foundational validation based on electromagnetic principles and stands as a phenomenological theory relying on fitted coupling coefficients. We employ an ab initio Maxwellian approach using quasinormal-mode theory to derive an "exact" Maxwell evolution (EME) equation for resonator dynamics. While the resulting differential equation bears resemblance to the classical one, it introduces novel terms embodying distinct physics, suggesting that the CMT predictions could be faulted by dedicated experiments, for instance carried out with short and off-resonance pulses, or with resonators of sizes comparable to or greater than the wavelength. Nonetheless, our examination indicates that, despite its inherent lack of strictness, the CMT enables precise predictions for numerous experiments due to the flexibility provided by the fitted coupling coefficients. The new EME equation is anticipated to be applicable to all electromagnetic resonator geometries, and the theoretical approach we have taken can be extended to other wave physics.

physics.optics↗

arXiv2023

Dispersive Perfectly Matched Layer and high order Absorbing Boundary Conditions for the computation of Quasinormal modes of open electromagnetic structures

Resonances, also known as quasinormal modes (QNM) in the non-Hermitian case, play a ubiquitous role in all domains of physics ruled by wave phenomena, notably in continuum mechanics, acoustics, electrodynamics, and quantum theory. The non-Hermiticity arises from the system losses, whether they are material (Joule losses in electromagnetism) or linked to the openness of the problem (radiation losses). In this paper, we focus on the latter delicate matter when considering bounded computational domains mandatory when using e.g. Finite Elements. Dispersive perfectly matched layers and absorbing boundary conditions are studied.

physics.optics↗

arXiv2022

The visual appearances of disordered optical metasurfaces

Nanostructured materials have recently emerged as a promising approach for material appearance design. Research has mainly focused on creating structural colours by wave interference, leaving aside other important aspects that constitute the visual appearance of an object, such as the respective weight of specular and diffuse reflectances, object macroscopic shape, illumination and viewing conditions. Here, we report the potential of disordered optical metasurfaces for harnessing visual appearance. We develop a multiscale modelling platform for the predictive rendering of macroscopic objects covered by metasurfaces in realistic settings, showing how nanoscale resonances and mesoscale interferences can be used to spectrally and angularly shape reflected light and thus create unusual visual effects at the macroscale. We validate this property with realistic synthetic images of macroscopic objects and centimetre-scale samples observable with the naked eye. This framework opens new perspectives in many branches of fine and applied visual arts.

physics.optics↗

arXiv2022

Specular reflection and transmission of electromagnetic waves by disordered metasurfaces

Planar, disordered assemblies of small particles incorporated in layered media -- sometimes called ``disordered metasurfaces'' in the recent literature -- are becoming widespread in optics and photonics. Their ability to scatter light with exotic angular and spectral features in reflection and transmission, as well as their suitability to scalable fabrication techniques, makes them promising candidates for certain applications, ranging from thin-film photovoltaics to visual appearance design. This chapter introduces the basic concepts and theoretical models for the specular (a.k.a. coherent) reflectance and transmittance of electromagnetic waves by disordered metasurfaces. After describing the classical scattering formalism for discrete media, we establish known analytical expressions for the reflection and transmission coefficients of disordered particle monolayers on layered substrates. Two classical models, based on the independent scattering approximation (ISA) and the effective field approximation (EFA), are presented. Their accuracy is examined by comparing predictions with those obtained from rigorous full-wave computations using an in-house multiple-scattering code. This chapter may serve as a starting point to students and researchers who wish to dive into the topic and explore the potential of disordered metasurfaces for applications.

physics.optics↗