arXiv subjects

Giuseppe Strangi

Publications and source records attributed to Giuseppe Strangi.

At least 19 recordsLinked to original sources

arXiv2026

Enhancing FRET through DNA-controlled Emitters and ENZ Metamaterials

The ability to significantly enhance energy transfer processes at the nanoscale requires the simultaneous optimization of molecular-scale orientation and macroscopic photonic enhancement between multiple quantum emitters. However, achieving this dual control has remained a significant experimental challenge, often limited by the stochastic arrangement of emitter assemblies and spatially non-uniform electromagnetic fields in conventional photonic platforms. In this work, we demonstrate a unified architecture that achieves this synergy by combining the structural precision of DNA nanotechnology with the unique field environment generated by epsilon-near-zero (ENZ) materials. Using DNA molecular beacons as programmable emitter scaffolds, we establish fixed donor-acceptor separations and emitter orientations (Atto425/Cy3.5) in two well-defined conformational states: closed hairpin (emitter separation 2 nm) and extended (8.16 nm) configurations. These structures are then embedded in the near-field of a multilayer ENZ metamaterial substrate, which facilitates spatially uniform, enhanced electromagnetic field coupling. Time-resolved photoluminescence measurements demonstrate a significant increase in FRET efficiency for DNA-programmed emitter pairs in the ENZ environment, compared to those on a glass substrate, corresponding to increased donor quenching and shortened donor lifetime. These results establish a scalable experimental pathway for engineering light-matter interactions at molecular scales with applications in next-generation biosensing and quantum photonic technologies.

physics.optics↗

arXiv2026

Observation of Light-Driven Levitation Near Epsilon-Near-Zero Surfaces

Optical manipulation of micro- and nanoparticles near surfaces is fundamental for applications in sensing and microfluidics, yet controlling particle-surface interactions remains challenging. Here we experimentally investigate light-induced forces on dielectric particles near epsilon-near-zero (ENZ) metamaterial surfaces using photonic force microscopy. By illuminating trapped particles with tunable visible light, we observe a wavelength-dependent repulsive force unique to ENZ surfaces, contrasting with the attractive forces near dielectric or metallic substrates. This repulsion peaks near the ENZ frequency and may be attributed to combined optical ENZ effects and thermophoretic forces. Our findings demonstrate that ENZ metamaterials can induce stable levitation of particles via light-driven forces, offering a novel mechanism for contactless manipulation in microfluidic environments. This work advances understanding of light-matter interactions at ENZ interfaces and suggests potential for ENZ-based optical control of micro- and nanoscale objects, with potential applications in micro- and nanofluidic environments.

physics.optics↗

arXiv2025

Directional Random Lasing in Liquid Crystal Infiltrated Metasurfaces

Random lasers (RL) emit light through multiple scattering in disordered gain media, typically resulting in isotropic emission with limited directionality control. Controlling RL emission direction in compact systems remains a challenge. Here we report directional random lasing achieved by infiltrating dye-doped nematic liquid crystals into a nanostructured silica metasurface. By adjusting pump energy, we induce a transition from uniform angular photoluminescence to a strongly directional emission peak at large angles in the amplified spontaneous emission and RL regimes. This directionality arises from enhanced spatial coherence in the strong scattering regime, enabling coupling of guided random-laser modes to high-angle diffraction through the metasurface grating. Our system demonstrates wide-angle RL beam steering at submicron scale without complex external components. These results provide a straightforward method to control RL emission directionality, advancing tunable coherent light sources and metasurface-based photonic applications.

physics.optics↗

arXiv2025

Plasmonic Metasurfaces with Structural Chirality and Pseudo-Chirality for Enhanced Circular Dichroism and Enantiomeric Recognition

We present the design and optical characterization of a plasmonic metasurface engineered to exhibit strong polarization anisotropy under both linearly and circularly polarized light. The metasurface consists of geometrically asymmetric gold nanostructures arranged periodically on a glass substrate. Each nanostructure is formed by the fusion of three equilateral triangles. The nanostructures simultaneously break mirror and inversion symmetries, resulting in chiral and pseudo-chiral optical responses that manifest as linear and circular polarization-dependent spectral features. Our numerical and experimental results reveal clear chiroptical effects in both near- and far-field. Near-field scanning optical microscopy confirms the excitation of polarization-selective localized plasmonic modes, with spatially distinct hot-spots lighting up under different incident polarizations. Furthermore, we demonstrate that the metasurface exhibits a measurable enantiospecific optical response when coated with thin left- or right-handed chiral overlayers. The differential circular dichroism signals observed in the presence of opposite enantiomers highlight the potential of the metasurface for label-free chiral sensing. These findings provide new insights into the interplay between structural anisotropy, pseudo-chirality, and enantioselective interactions in planar plasmonic systems. Our findings highlight the ability of planar metasurfaces to emulate chiral optical behavior without requiring volumetric 3D structures.

physics.optics↗

arXiv2024

Intervalence Plasmons in Boron-Doped Diamond

Doped semiconductors can exhibit metallic-like properties ranging from superconductivity to tunable localized surface plasmon resonances. Diamond is a wide-bandgap semiconductor that is rendered electronically active by incorporating a hole dopant, boron. While the effects of boron doping on the electronic band structure of diamond are well-studied, any link between charge carriers and plasmons, has never been shown. Here, we report intervalence plasmons in boron-doped diamond, defined as collective electronic excitations between the valence subbands, opened up by the presence of holes. Evidence for these low-energy excitations is provided by valence electron energy loss spectroscopy and near-field infrared spectroscopy. The measured spectra are subsequently reproduced by first-principles calculations based on the contribution of intervalence band transitions to the dielectric function. Our calculations also reveal that the real part of the dielectric function exhibits a crossover characteristic of metallicity. These results suggest a new mechanism for inducing plasmon-like behavior in doped semiconductors, and the possibility of attaining such properties in diamond, a key emerging material for quantum information technologies.

cond-mat.mtrl-sci↗

arXiv2023

Unveiling Chirality: Exploring Nature's Blueprint for Engineering Nanostructured Materials

Chirality, the property of asymmetry, is of great importance in biological and physical phenomena. This prospective offers an overview of the emerging field of chiral bioinspired plasmonics and metamaterials, aiming to uncover nature's blueprint for engineering nanostructured materials. These materials possess unique chiral structures, resulting in fascinating optical properties and finding applications in sensing, photonics, and catalysis. The first part of the prospective focuses on the design and fabrication of chiral metamaterials that mimic intricate structures found in biological systems. By employing self-assembly and nanofabrication techniques, researchers have achieved remarkable control over the response to light, opening up new avenues for manipulating light and controlling polarization. Chiral metamaterials hold significant promise for sensing applications, as they can selectively interact with chiral molecules, allowing for highly sensitive detection and identification. The second part delves into the field of plasmonics nanostructures, which mediate enantioselective recognition through optical chirality enhancement. Plasmonic nanostructures, capable of confining and manipulating light at the nanoscale, offer a platform for amplifying and controlling chirality-related phenomena. Integrating plasmonic nanostructures with chiral molecules presents unprecedented opportunities for chiral sensing, enantioselective catalysis, and optoelectronic devices. By combining the principles of chiral bioinspired plasmonics and metamaterials, researchers are poised to unlock new frontiers in designing and engineering nanostructured materials with tailored chiroptical properties.

physics.optics↗

arXiv2022

Manipulating Random Lasing Correlations in Doped Liquid Crystals

Random lasers are highly configurable light sources that are promising for imaging and photonic integration. In this study, random lasing action was generated by optically pumping MBBA liquid crystals infiltrated with gold nanoparticles and laser dye (pyrromethene 597). By varying the pump energy near lasing threshold, we show that it is possible to control the intensity correlations between the random lasing modes. The correlations in the system were phenomenologically characterized using the L\'evy statistics of the emission spectra survival function. We also find that correlations and persistence of lasing action are correlated. These results demonstrate the possibility to dynamically control a key physical feature of random lasers, which may find applications in biomedical settings and network communications.

physics.optics↗

arXiv2022

Fano Resonant Optical coatings platform for Full Gamut and High Purity Structural Colors

Structural coloring is a photostable and environmentally friendly coloring approach that harnesses optical interference and nanophotonic resonances to obtain colors with a range of applications including steganography, d\'ecor, data storage, and anticounterfeiting measures. We show that optical coatings exhibiting the photonic Fano Resonance is an ideal platform for structural coloring -- it provides full color access, high color purity, high brightness, controlled iridescence, and scalable manufacturability. We show that an additional oxide film deposited on Fano resonant optical coatings (FROCs) increases the color purity (up to 97%) and color gamut coverage range (> 99% coverage of the sRGB and Adobe color spaces). For coloring applications that do not require high spatial resolution, FROCs provide a significant advantage over existing structural coloring schemes.

physics.optics↗

arXiv2022

All-Optical tunability of metalenses infiltrated with liquid crystals

Metasurfaces have been extensively engineered to produce a wide range of optical phenomena, allowing unprecedented control over the propagation of light. However, they are generally designed as single-purpose devices without a modifiable post-fabrication optical response, which can be a limitation to real-world applications. In this work, we report a nanostructured planar fused silica metalens permeated with a nematic liquid crystal (NLC) and gold nanoparticle solution. The physical properties of embedded NLCs can be manipulated with the application of external stimuli, enabling reconfigurable optical metasurfaces. We report all-optical, dynamic control of the metalens optical response resulting from thermo-plasmonic induced changes of the NLC solution associated with the nematic-isotropic phase transition. A continuous and reversible tuning of the metalens focal length is experimentally demonstrated, with a variation of 80 um (0.16% of the 5 cm nominal focal length) along the optical axis. This is achieved without direct mechanical or electrical manipulation of the device. The reconfigurable properties are compared with corroborating numerical simulations of the focal length shift and exhibit close correspondence.

physics.optics↗

arXiv2021

General Inverse Design of Thin-Film Metamaterials With Convolutional Neural Networks

The design of metamaterials which support unique optical responses is the basis for most thin-film nanophotonics applications. In practice this inverse design problem can be difficult to solve systematically due to the large design parameter space associated with general multi-layered systems. We apply convolutional neural networks, a subset of deep machine learning, as a tool to solve this inverse design problem for metamaterials composed of stacks of thin films. We demonstrate the remarkable ability of neural networks to probe the large global design space (up to $10^{12}$ possible parameter combinations) and resolve all relationships between metamaterial structure and corresponding ellipsometric and reflectance / transmittance spectra. The applicability of the approach is further expanded to include the inverse design of synthetic engineered spectra in general design scenarios. Furthermore, this approach is compared with traditional optimization methods. We find an increase in the relative optimization efficiency of the networks with increasing total layer number, revealing the advantage of the machine learning approach in many-layered systems where traditional methods become impractical.

physics.comp-ph↗

arXiv2021

Magnetic Circular Dichroism in Hyperbolic Metamaterial Nanoparticles

The optical properties of some nanomaterials can be controlled by an external magnetic field, providing active functionalities for a wide range of applications, from single-molecule sensing to nanoscale nonreciprocal optical isolation. Materials with broadband tunable magneto-optical response are therefore highly desired for various components in next-generation integrated photonic nanodevices. Concurrently, hyperbolic metamaterials received a lot of attention in the past decade since they exhibit unusual properties that are rarely observed in nature and provide an ideal platform to control the optical response at the nanoscale via careful design of the effective permittivity tensor, surpassing the possibilities of conventional systems. Here, we experimentally study magnetic circular dichroism in a metasurface made of type-II hyperbolic nanoparticles on a transparent substrate. Numerical simulations confirm the experimental findings, and an analytical model is established to explain the physical origin of the observed magneto-optical effects, which can be described in terms of the coupling of fundamental electric and magnetic dipole modes with an external magnetic field. Our system paves the way for the development of nanophotonic active devices combining the benefits of sub-wavelength light manipulation in hyperbolic metamaterials supporting a large density of optical states with the ability to freely tune the magneto-optical response via control over the anisotropic permittivity of the system.

physics.optics↗

arXiv2021

Glioblastoma Treatments with Photo-Nanotherapeutics Induce Massive Devascularization and Tumor Elimination

Glioblastoma multiforme (GBM) is one of the deadliest and most aggressive cancers, remarkably resilient to current therapeutic treatments. Here, we report in vivo studies of GBM treatments based on photo-nanotherapeutics able to induce synergistic killing mechanisms. Core-shell nanoparticles have been weaponized by combining the photophysical properties of an Ir(III) complex - a new generation PDT agent - with the thermo-plasmonic effects of resonant gold nanospheres. To investigate the damages induced in GBM treated with these nanosystems and exposed to optical radiation, we recurred to the X-ray phase contrast tomography (XPCT). This high-resolution 3D imaging technique highlighted a vast devascularization process by micro-vessels disruption, which is responsible of a tumor elimination without relapse.

physics.app-ph↗

arXiv2020

Designer Bloch Plasmon Polariton Dispersion in Hyperbolic Meta-Gratings

Hyperbolic metamaterials (HMMs) represent a novel class of fascinating anisotropic plasmonic materials, supporting highly confined propagating plasmon polaritons in addition to surface plasmon polaritons. However, it is very challenging to tailor and excite these modes at optical frequencies by prism coupling because of the intrinsic difficulties in engineering non-traditional optical properties with artificial nanostructures and the unavailability of high refractive index prisms for matching the momentum between the incident light and the guided modes. Here, we report the mechanism of excitation of high-k Bloch-like Plasmon Polariton (BPPs) modes with ultrasmall modal volume using a meta-grating, which is a combined structure of a metallic diffraction grating and a type II HMM. We show how a 1D plasmonic grating without any mode in the infrared spectral range, if coupled to a HMM supporting high-k modes, can efficiently enable the excitation of these modes via coupling to far-field radiation. Our theoretical predictions are confirmed by reflection measurements as a function of angle of incidence and excitation wavelength. We introduce design principles to achieve a full control of high-k modes in meta-gratings, thus enabling a better understanding of light-matter interaction in this type of hybrid meta-structures. The proposed spectral response engineering is expected to find potential applications in bio-chemical sensors, integrated optics and optical sub-wavelength imaging.

physics.optics↗

arXiv2020

Biomolecular sensing at the interface between chiral metasurfaces and hyperbolic metamaterials

In recent years significant efforts have been made to design and fabricate functional nanomaterials for biomedical applications based on the control of light matter interaction at the nanometer scale. Among many other artificial materials, hyperbolic dispersion metamaterials allow to access unprecedented physical effects and mechanisms due to the extreme anisotropy of their optical constants. The unbound isofrequency surface of hyperbolic metamaterials (HMMs) enable the possibility to support a virtually infinite density of states and ultra-high confinement of electromagnetic fields, allowing perfect absorption of light and extreme sensing properties. Optical sensor technology based on plasmonic metamaterials offers significant opportunities in the field of clinical diagnostics, particularly for the detection of low-molecular-weight biomolecules in highly diluted solutions. In this context, we present a computational effort to engineer a biosensing platform based on hyperbolic metamaterials, supporting highly confined bulk plasmon modes integrated with out-of-plane chiral metasurfaces. The role of the helicoidal chiral metasurface is manifold: i) as a diffractive element to increase the momentum of the incoming light to excite the plasmon sensing modes with linearly and circularly polarized light; ii) as out-of-plane extended sensing surface to capture target analytes away from the substrate thereby the diffusion limit; iii) as a plamonic chiral nanostructure with enhanced sensing performance over circularly polarized reflectance light.

physics.app-ph↗

arXiv2020

Hydrogen gas sensing using aluminum doped ZnO metasurface

Hydrogen sensing is crucial in a wide variety of areas, such as industrial, environmental, energy and biomedical applications. However, engineering a practical, reliable, fast, sensitive and cost-effective hydrogen sensor, is a persistent challenge. Here we demonstrate hydrogen sensing using aluminum-doped zinc oxide (AZO) metasurfaces based on optical read-out. The proposed sensing system consists of highly ordered AZO nanotubes (hollow pillars) standing on a SiO2 layer deposited on a Si wafer. Upon exposure to hydrogen gas, the AZO nanotube system shows a wavelength shift in the minimum reflectance by 13 nm within 10 minutes for a hydrogen concentration of 4%. These AZO nanotubes can also sense the presence of a low concentration (0.7 %) of hydrogen gas within 10 minutes. Its rapid response time even for low concentration, the possibility of large sensing area fabrication with good precision, and high sensitivity at room temperature make these highly ordered nanotube structures a promising miniaturized H2 gas sensor.

physics.app-ph↗

arXiv2019

Manipulating Acoustic and Plasmonic Modes in Gold Nanostars

In this contribution experimental evidence of plasmonic edge modes and breathing acoustic modes in gold nanostars (AuNS) is reported. AuNS are synthesized in a surfactant-free, one-step wet-chemistry method. Optical extinction measurements of AuNS confirm the presence of localized surface plasmon resonances (LSPRs), while electron energy-loss spectroscopy (EELS) in the scanning transmission electron microscope (STEM) shows the spatial distribution of LSPRs and reveals the presence of acoustic breathing modes. Plasmonic hot-spots generated at the pinnacle of the sharp spikes, due to the optically active edge dipolar mode, allow significant intensity enhancement of local fields, hot-electron injection, and thus useful for size detection of small protein molecules. The breathing modes observed away from the apices of the nanostars are identified as stimulated dark modes - they have an acoustic nature - and likely originate from the confinement of the surface plasmon by the geometrical boundaries of a nanostructure. The presence of both types of modes is verified by numerical simulations. Both these modes offer the possibility to design nanoplasmonic antenna based on AuNS, which can provide information both on mass and polarizability of biomolecules using a two-step molecular detection process.

cond-mat.mes-hall↗

arXiv2019

Generalized Brewster-angle effect in thin-film optical absorbers and its application for graphene hydrogen sensing

Generalized Brewster angle (GBA) is the incidence angle at which polarization by reflection for p- and s-polarized light takes place. Realizing s-polarization Brewster effect requires a material with magnetic response which is challenging at optical frequencies since the magnetic response of materials at these frequencies is extremely weak. Here, we experimentally realize GBA effect in the visible using a thin-film absorber system consisting of a dielectric film on an absorbing substrate. Polarization by reflection is realized for both p- and s- polarized light at different angles of incidence and multiple wavelengths. We provide a theoretical framework for the generalized Brewster effect in thin-film light absorbers. We demonstrate hydrogen gas sensing using a single layer graphene film transferred on a thin-film absorber at the GBA with ~1 fg/mm2 aerial mass sensitivity. The ultrahigh sensitivity stems from the strong phase sensitivity near point of darkness, particularly at the GBA, and the strong light-matter interaction in planar nanocavities. These findings depart from the traditional domain of thin-films as mere interference optical coatings and highlight its many potential applications including gas sensing and biosensing.

physics.optics↗

arXiv2019

Cooperative energy transfer controls the spontaneous emission rate beyond field enhancement limits

Quantum emitters located in proximity to a metal nanostructure individually transfer their energy via near-field excitation of surface plasmons. The energy transfer process increases the spontaneous emission (SE) rate due to plasmon-enhanced local field. Here, we demonstrate significant acceleration of quantum emitter SE rate in a plasmonic nano-cavity due to cooperative energy transfer (CET) from plasmon-correlated emitters. Using an integrated plasmonic nano-cavity, we realize up to six-fold enhancement in the emission rate of emitters coupled to the same nano-cavity on top of the plasmonic enhancement of the local density of states. The radiated power spectrum retains the plasmon resonance central frequency and lineshape, with the peak amplitude proportional to the number of excited emitters indicating that the observed cooperative SE is distinct from super-radiance. Plasmon-assisted CET offers unprecedented control over the SE rate and allows to dynamically control the spontaneous emission rate at room temperature enabling an SE rate based optical modulator.

cond-mat.mes-hall↗