arXiv subjects

Olivier J. F. Martin

Publications and source records attributed to Olivier J. F. Martin.

At least 19 recordsLinked to original sources

arXiv2026

Simulations of Fluorescence and Energy Transfer in Periodic Systems: Pitfalls and Considerations for Bound States in the Continuum

Bound states in the continuum (BICs) combine high quality factors with strong electromagnetic-field localization and are therefore widely explored for enhancing light--matter interactions. However, large field amplitudes do not directly translate into useful fluorescence enhancement or energy transfer enhancement between two donor--acceptor fluorophores. Here, we investigate this question for a hybrid plasmonic--photonic resonant waveguide grating supporting a symmetry-protected BIC. We emphasize some of the pitfalls associated with the numerical simulations, especially the utilization of periodic boundary conditions for fluorescence. Strong BIC-related fields can enhance acceptor absorption while useful fluorescence enhancement remains moderate. Extensive simulations and the comparison of different figures of merit, indicate that, while a BIC can suppress radiative leakage, it can also redirect a large fraction of the energy into Ohmic losses. As a result, the useful fluorescence enhancement of donors remains moderate, whereas absorption by acceptors can be strongly enhanced in Förster resonance energy transfer (FRET) experiments. It is essential to separate near-field FRET from long-range energy transfer and reabsorption mechanisms, both of which are mediated by the delocalized BIC mode. Finally, results obtained for finite gratings are compared with infinite periodic simulations and conceptual inconsistencies explained. This work provides a consistent framework for interpreting fluorescence, absorption, and energy transfer in BIC-based periodic nanophotonic systems.

physics.optics↗

arXiv2026

Geometry-Encoded Multireceiver Fluorometry Enables Full-Range Nonlinear Quantification under the Inner Filter Effect

The inner filter effect (IFE) transforms the nominally linear fluorescence-concentration relationship into a geometry-dependent and often nonmonotonic response, resulting in reduced sensitivity, concentration ambiguity, and inaccurate underestimation at high optical densities. Here, we introduce a spatially encoded multireceiver fluorometric strategy that does not eliminate or correct the IFE, but instead harnesses the spatial fluorescence attenuation induced by IFE as an additional quantitative encoding dimension. Fluorescence generated along the excitation axis is integrated over independently positioned receiver windows, and concentration is recovered by nonlinear optimization of the joint fluorescent intensity vector. Tryptophan was selected as a biomedically relevant model fluorophore to validate the proposed strategy. Single-window calibration exhibited vanishing-gradient boundary and two-valued concentration inversions, whereas two spatially separated receiver windows restored global identifiability across the full concentration range. Screening of 35 two-receiver geometries identified the minimum-uncertainty configuration, achieving an average 95% error half-width of mean E_95= 0.884 mg/L, and the maximum-sensitivity configuration, reaching a noise-normalized response sensitivity of mean S_N=3.832 a.u./(mg/L). By converting spatial attenuation into a multidimensional concentration coordinate, this approach extends quantitative fluorescence analysis without dilution, a separate absorbance measurement, or piecewise calibration and provides a general metrology framework for fluorescence metrology even under strong IFE conditions.

physics.optics↗

arXiv2026

Crystalline metal flakes: Platforms for advanced plasmonics and hybrid 2D material architectures

Crystalline noble metal flakes are emerging as versatile platforms in nanophotonics, enabling a broad range of optical phenomena and applications. Their atomically flat surfaces, high crystallinity, and superior optical quality open new avenues in advanced plasmonics, quantum light generation, and hybrid photonic systems. In contrast to conventional polycrystalline metal films, which typically suffer from higher optical losses due to grain boundaries, surface roughness, and structural disorder, these monocrystalline flakes provide minimal scattering and enhanced performance. They serve as templates for precise nanostructuring through techniques like focused-ion beam (FIB) milling and are crucial for advanced applications in sensing and optoelectronics. Additionally, they facilitate frontier research in quantum plasmonics, enabling fundamental studies of nonlocal optical effects and the generation of nonclassical light. Furthermore, the well-defined $\{111\}$ facets of these flakes host Tamm--Shockley surface states that support 2D plasmons coexisting with bulk modes. At near-infrared wavelengths and beyond, crystalline flakes act as nearly ideal metallic mirrors, featuring surface roughness limited only to atomic terrace steps, making them highly suitable for integration with 2D materials in hybrid photonic architectures. This review surveys the key roles these flakes play, highlighting recent developments and discussing future prospects while emphasizing their unique benefits in addressing fundamental and applied challenges in modern nanophotonics.

physics.optics↗

arXiv2026

Engineering Photoluminescence with Mie Voids

Spontaneous emission, as a fundamental radiative process and a versatile information carrier, plays a vital role in light-emitting devices, optical information modulation and encryption, super-resolution fluorescence imaging. Engineering the photonic environment surrounding photon emitters enables control over their emission properties. However, simultaneously achieving precise engineering of both excitation enhancement and quantum-yield modulation at the nanoscale remains elusive, highlighting substantial room for advancing the precise orchestrating of photoluminescence. Here, we introduce silicon Mie voids - air-defined cavities that invert the conventional solid-particle geometry - to achieve independent tuning of photoluminescence within a single subwavelength unit, while minimizing optical losses. Full-wave simulations and experiments on both gradient and uniform Mie-void arrays jointly validate this quantitative framework for spontaneous emission tuning, which disentangles excitation enhancement arising from local field confinement in air and quantum-yield enhancement resulting from strengthened emitter-resonator coupling, while confirming the accelerated radiative decay enabled by the modified optical LDOS. Leveraging this flexible mechanism, we realize a multimodal nanophotonic pattern with near-diffraction-limited pixels that encode the EPFL logo in the bright field and the SJTU logo in both dark field and photoluminescence maps. These results establish Mie voids as a powerful platform for high-density multimodal encrypted displays and open new avenues for advancing state-of-the-art nanophotonic devices.

physics.optics↗

arXiv2026

Non-Hermitian fluctuations enable model-free particle manipulation

Contactless manipulation of microscopic matter is central to applications ranging from the isolation of circulating tumor cells in liquid biopsies to the removal of microplastics from environmental water. Electromagnetic approaches are particularly attractive because fields can be structured within compact microfluidic systems using either light or simple electrode architectures. However, precise manipulation requires calibrated models of the field distribution and accurate knowledge of the properties of both the object and the surrounding medium, which limits applicability to well-characterized, static systems. Here we show that energy dissipation itself provides sufficient information for deterministic particle control. Instead of relying on explicit field calibration, our approach exploits an original relationship between particle position, energy dissipation, and electromagnetic body forces, which can be accessed experimentally through variations of conductance matrices. By extracting force-shaping voltage patterns from these measurements, we demonstrate fully automated closed-loop manipulation of silica microbeads in one and two dimensions, including in the presence of other freely moving particles in a disordered background. These results establish a pathway toward deterministic force control by deliberately measuring and exploiting the non-Hermitian response of the system to engineer electromagnetic momentum transfer. This framework expands micromanipulation into realistic, dynamically evolving environments, where wave-matter interactions cannot be fully pre-characterized or eliminated through design.

physics.app-ph↗

arXiv2026

Plasmon Induced Delocalized Second-Harmonic Generation Towards Buried-Interface Spectroscopy

Second-harmonic generation microscopy is a powerful technique capable of probing local crystal symmetries and electric fields at interfaces. However, it often suffers from weak signal strength and is difficult to understand in multilayer systems where many materials can give competing signal contributions. In this work we present direct observation of delocalized, surface plasmon polariton-mediated second-harmonic generation on gold monocrystalline surfaces and structures. We generate second-harmonic light up to 35 um from the excitation spot and, excitingly, we obtain signal from atomically flat surfaces without a fundamental excitation beam present in the same region. We reveal that this process arises from the interaction of two counter-propagating surface plasmon polaritons, which we believe to be the first observation of this process at the microscale. This signal has the same polarisation dependence as localised second-harmonic generation and is emitted in a collimated beam travelling perpendicular to the sample surface. In part due to local electric field enhancements, we were able to observe these signals on a CMOS camera with 1 s exposure and no gain using an industrial-grade pulsed laser. Our results enable wide area multilayer samples to be probed using a single excitation beam, with applications including in energy, catalysis and single particle surface sensing.

physics.optics↗

arXiv2026

Retrieving intrinsic polarization anisotropies of nanostructures using differential Mueller matrix polarimetry

Accurate characterization of polarization dependent light matter interactions in nanostructured systems is paramount for the development of chiral metasurfaces. It is also often challenging, because multiple anisotropic mechanisms, such as linear and circular diattenuation, birefringence, and depolarization can coexist and couple with one another. Conventional ellipsometric and chiro optical techniques typically assume isolated polarization effects and can therefore yield inaccurate estimates of the intrinsic polarization parameters. Here, we demonstrate that Mueller matrix polarimetry combined with a differential Mueller matrix decomposition provides a robust framework for retrieving the intrinsic polarization response of complex nanophotonic systems. Using plasmonic gammadion arrays and media with multiple polarization anisotropies as multi modal chiral platforms, we show that simultaneous linear and circular anisotropies produce coupled signatures in the Mueller matrix, leading to significant artifacts in conventional polarization observables. Through analytical modeling and experimental measurements, we quantify these artifacts and demonstrate that a differential decomposition accurately decouples and retrieves the underlying polarization parameters. The presented approach also successfully probes the polarization anisotropic effects in inhomogeneous media enabling a clear discrimination between the intrinsic chiral optical response and geometric phase effects arising from spin orbit interaction of light in momentum resolved scattering. These results establish differential Mueller matrix polarimetry as a powerful tool for rigorous characterization of polarization phenomena in nanostructured photonic systems and polarization engineered metasurfaces.

physics.optics↗

arXiv2026

HELIOS: A surface integral equation software for light scattering in homogeneous, periodic, and stratified environments

We present HELIOS (HomogEneous and Layered medIa Optical Scattering), an open-source surface integral equation (SIE) software designed for modeling light scattering by particles embedded in homogeneous or layered media and periodic backgrounds. The code implements the Poggio-Miller-Chang-Harrington-Wu-Tsai (PMCHWT) formulation that has demonstrated exceptional reliability in solving scattering problems with penetrable objects. Domain boundaries are discretized using triangular meshes, upon which the electric and magnetic surface current densities are expanded using the Rao-Wilton-Glisson (RWG) basis functions. For periodic structures, such as photonic crystals and metasurfaces, HELIOS employs Ewald's transformation to efficiently evaluate the infinite series associated with 2D lattices. Regarding stratified media, the code utilizes a matrix-friendly approach for the layered media Green's tensor, computing Sommerfeld integrals and accelerating calculations through a tabulation-interpolation scheme. The source code is implemented in C++, while a Python interface manages the workflow, including simulation setup, solver run, and post-processing. The accuracy and versatility of HELIOS are demonstrated through various examples that cover all its functionalities.

physics.optics↗

arXiv2026

Wavefront Control and Intensity Modulation of Third Harmonic Generation in Nonlocal Metasurfaces

Metasurfaces have emerged as a promising platform for integrated nonlinear optics. Nonlocal metasurfaces enable high nonlinear conversion efficiency, while the local ones can offer versatile wavefront control, yet achieving both within a single metasurface remains challenging. Here, using a nonlocal phase gradient metasurface, we firstly demonstrate efficient third harmonic generation (THG) with polarization-dependent wavefront control. Leveraging nonlocal nonlinear geometric phase existing at resonance, the third harmonic light with distinct polarizations is deflected into $\pm$ 2nd and $\pm$ 4th diffraction orders, simultaneously achieving a conversion efficiency up to $1.45\times 10^{-4}$ under a pump intensity of $1 GW/cm^{2}$. Then, by introducing a secondary fundamental beam, whose generated third harmonic light overlaps with that of the first beam, the intensity modulation of THG is obtained. The THG efficiency can be tuned from $3.9 \times 10^{-9}$ to $5.5 \times 10^{-3}$ by varying the relative phase, polarization and intensity of two fundamental beams. Through utilizing the advantages of both local and nonlocal metasurfaces, our results effectively pave the way to on-chip nonlinear photonic devices and signal processing.

physics.optics↗

arXiv2025

Scalable Generalized Meta-Spanners Enabling Parallel Multitasking Optical Manipulation

Optical manipulation techniques offer exceptional contactless control but are fundamentally limited in their ability to perform parallel multitasking. To achieve high-density, versatile manipulation with subwavelength photonic devices, it is essential to sculpt light fields in multiple dimensions. Here, we overcome this challenge by introducing generalized optical meta-spanners (GOMSs) based on metasurfaces. Relying on complex-amplitude modulation, this platform generates lens-free, customizable optical fields that suppress diffractive losses. As a result, several advanced functionalities are simultaneously achieved, including longitudinally varying manipulation and in-plane spanner arrays, which outperforms the same operations realized by conventional donut-shaped orbital flows. Furthermore, the particle dynamics is reconfigurable simply by switching the input and output polarizations, facilitating robust multi-channel control. We experimentally validate the proposed approach by demonstrating single-particle dynamics and the parallel manipulation of particle ensembles, revealing exceptional stability for multitasking operations. These results demonstrate an ultracompact platform scalable to a much larger number of optical spanners, advancing metadevices from wavefront sculptors to particle manipulators. We envision that the GOMS will catalyze innovations in cross-disciplinary fields such as targeted drug delivery and cell-level biomechanics.

physics.optics↗

arXiv2024

Step Function in Momentum Space by a Metagrating

Metasurface research has shown significant potential for controlling the polarization, amplitude, phase and propagation direction of light. Nevertheless, control over the angular response of incident light still remains a long-standing problem. In this work, we show the potential of diffractive systems for obtaining a step function in momentum space where the mirror symmetry of the angular transmittance is broken. By engineering the scattering response of an asymmetric particles in a metagrating, we could obtain such a step function in a passive, reciprocal, and lossless fashion. More specifically, the metagrating performs filtering in the momentum space with an abrupt switching from reflection to transmission for an incident electromagnetic wave with an arbitrary spatial profile. This metagrating may find diverse applications in the context of optical spatial analog computing. Moreover, it paves the way for exploring the capabilities of diffractive systems for gaining full control over the angular response of light using arbitrary momentum transfer functions.

physics.optics↗

arXiv2024

Electromagnetic manipulation of sub-500 Da biomolecules

The manipulation of nanoscale matter has the potential to revolutionize a variety of fields across nanoscience and technology. Here, we demonstrate experimentally and characterize numerically a device that combines the benefits of dielectrophoresis (DEP) - long-range and strong trapping forces - with those of plasmonic tweezers - high sensitivities - to achieve a remarkable efficiency in the trapping and sensing of metallic nanoparticles and biomolecules. In particular, we show the DEP trapping and surface enhanced Raman scattering characterization of bovine serum albumin and Rhodamine B, thus extending the applications of tweezing devices to molecules having masses of only a few hundreds of Da. This range covers virtually any molecule relevant for life, from tiny oligopeptides to large proteins. This pushes our manipulation capabilities deep into the realms of efficient single-molecule biosensing and quantum science, providing a powerful platform to probe matter at the nanoscale.

cond-mat.mes-hall↗

arXiv2024

Visual and quantitative analysis of the trapping volume in dielectrophoresis of nanoparticles

Nanoparticle manipulations require a careful analysis of the forces at play. Unfortunately, traditional force measurement techniques based on the particle velocity do not provide a sufficient resolution, while balancing approaches involving counteracting forces are often cumbersome. Here, we demonstrate that a nanoparticle dielectrophoretic response can be quantitatively studied by a straightforward visual delineation of the dielectrophoretic trapping volume. We reveal this volume by detecting the width of the region depleted of gold nanoparticles by the dielectrophoretic force. Comparison of the measured widths for various nanoparticle sizes with numerical simulations obtained by solving the particle-conservation equation shows excellent agreement, thus providing access to the particles physical properties, such as polarizability and size. These findings can be further extended to investigate various types of nano-objects $-$ including bio- and molecular aggregates $-$ and offer a robust characterization tool that can enhance the control of matter at the nanoscale.

physics.app-ph↗

arXiv2023

Multipolar Pseudochirality Induced Optical Torque

It has been observed that achiral nano-particles, such as flat helices, may be subjected to an optical torque even when illuminated by normally incident linearly polarized light. However, the origin of this fascinating phenomenon has so far remained mostly unexplained. We therefore propose an exhaustive discussion that provides a clear and rigorous explanation for the existence of such a torque. Using multipolar theory, and taking into account nonlocal interactions, we find that this torque stems from multipolar pseudochiral responses that generate both spin and orbital angular momenta. We also show that the nature of these peculiar responses makes them particularly dependent on the asymmetry of the particles. By elucidating the origin of this type of torque, this work may prove instrumental for the design of high-performance nano-rotors.

physics.optics↗

arXiv2023

Quadrupolar susceptibility modeling of substrated metasurfaces with application to the generalized Brewster effect

We derive generalized sheet transition conditions (GSTCs) including dipoles and quadrupoles, using generalized functions (distributions). This derivation verifies that the GSTCs are valid for metasurfaces in non-homogeneous environments, such as for practical metasurfaces fabricated on a substrate. The inclusion of quadrupoles and modeling of spatial dispersion provides additional hyper-susceptibility components which serve as degrees of freedom for wave transformations. We leverage them to demonstrate a generalized Brewster effect with multiple angles of incidence at which reflection is suppressed, along with an ``anti-Brewster'' effect where transmission is suppressed.

physics.optics↗

arXiv2023

Demonstration of a plasmonic nonlinear pseudo-diode

We demonstrate a nonlinear plasmonic metasurface that exhibits strongly asymmetric second-harmonic generation: nonlinear scattering is efficient upon excitation in one direction and it is substantially suppressed when the excitation direction is reversed, thus enabling a diode-like functionality. A significant (approximately 10 dB) extinction ratio of SHG upon opposite excitations is measured experimentally and those findings are substantiated with full-wave simulations. The combination of two commonly used metals - aluminium and silver - produces a material composition asymmetry that results into a bianisotropic response of the system, as confirmed by performing homogenization analysis and extracting an effective susceptibility tensor. Finally, we discuss the implications of our results from the more fundamental perspectives of reciprocity and time-reversal asymmetry.

physics.optics↗

arXiv2022

Mind the gap between theory and experiment

We discuss some examples where numerical simulations based on effectively fabricated nanostructures can provide additional insights into an experiment. Focusing on plasmonics, we study Fano resonant systems for optical trapping, realistic dipole antennas for near-field enhancement, and hybrid nanostructures that combine plasmonic metals with dielectrics refractive index sensing. For those systems, the same experimental detail can play a very different role, depending on the type of physical observable. For example, roughness can significantly influence the near-field, but be totally unnoticed in the far-field. It can affect molecules adsorbed on the surface, while refractive index sensing can be fully immune to such roughness. Approaching the experimental situation as closely as possible is certainly a challenging task and we demonstrate a simple approach based on SEM images for that. Altogether, bridging the gap between theory and experiment is not such a trivial task. However, some of the simple steps illustrated in this chapter can help build numerical models that match the experiment better.

physics.optics↗

arXiv2022

Spatial Symmetries in Multipolar Metasurfaces: From Asymmetric Angular Transmittance to Multipolar Extrinsic Chirality

We propose a framework that connects the spatial symmetries of a metasurface to its material parameter tensors and its scattering matrix. This provides a simple yet effective way to effortlessly determine properties of a metasurface scattering response, such as chirality or asymmetric transmission, and which of its effective material parameters should be taken into account in the prospect of a homogenization procedure. In contrast to existing techniques, this approach does not require any a priori knowledge of group theory or complicated numerical simulation schemes, hence making it fast, easy to use and accessible. Its working principle consists in recursively solving symmetry-invariance conditions that apply to dipolar and quadrupolar material parameters, which include nonlocal interactions, as well as the metasurface scattering matrix. The overall process thus only requires listing the spatial symmetries of the metasurface. Using the proposed framework, we demonstrate the existence of multipolar extrinsic chirality, which is a form of chiral response that is achieved in geometrically achiral structures sensitive to field gradients even at normal incidence.

physics.optics↗