arXiv subjects

Leonardo de S. Menezes

Publications and source records attributed to Leonardo de S. Menezes.

At least 19 recordsLinked to original sources

arXiv2026

Tunable hyperbolic metamaterials for brightening single-photon emission

Hyperbolic metamaterials (HMMs) are widely used to enhance spontaneous emission through their exceptionally large photonic density of states, yet large Purcell factors (>100) rarely translate into brighter emission, exposing both a practical limitation of HMMs as brightening platforms and a flaw in the Purcell factor itself as a figure of merit. Here we systematically evaluate spontaneous emission enhancement and photon outcoupling in metal-dielectric HMMs (TiO$_2$/Ag and phase-change Sb$_2$S$_3$/Ag) using effective medium theory, transfer matrix calculations, and full-wave FDTD simulations. We show that planar HMMs with Purcell factors exceeding 100 have external quantum efficiencies below 0.01, yielding an actual radiative Purcell factor (PF$_{rad}$) of only 1-2. Nanopatterning the HMM into a photonic crystal efficiently couples trapped high-k modes into free space, raising PF$_{rad}$ by an order of magnitude. Incorporating the phase-change material Sb$_2$S$_3$ further enables dynamic tuning of the hyperbolic spectral window and active control over emission brightness: an optimized nanostructured design reaches PF$_{rad}$ ~ 10-15 in the near-infrared, with switching contrast exceeding a factor of 15 upon phase transition. These results establish the radiative Purcell factor as a more reliable figure of merit than the conventional Purcell factor for engineering quantum emitters, and provide a practical route toward actively tunable, bright single-photon sources based on hyperbolic metamaterials.

physics.optics↗

arXiv2026

Dual-Gradient Plasmonic qBIC Metasurface for Time-Resolved In Situ Optimization of Molecular Vibrational Sensing in Water

Metaphotonic platforms based on quasi-bound states in the continuum (qBICs), harnessing strong near-field enhancement and deeply subwavelength field confinement, provide a versatile framework for surface-enhanced infrared absorption (SEIRA) spectroscopy. However, real-time molecular sensing in water using qBIC metasurfaces remains challenging. First, strong water absorption in the mid-infrared region damps qBICs and obscures weak analyte signals. Second, conventional metasurfaces rely on discrete arrays targeting individual wavelengths and coupling conditions, increasing the device footprint and fabrication effort required to match the qBIC to the molecular vibrational resonance. Here, we present a dual-gradient plasmonic qBIC metasurface with diamond-shaped resonators for in situ molecular vibrational sensing in water, where spatially encoded gradients in the scaling factor and asymmetry parameter independently control the qBIC spectral positions and radiative rates, respectively, across a 1000 um x 700 um footprint. Building on this capability, we experimentally monitor lipid vesicle dynamics in real time and resolve the carbonyl vibrational signature despite the unavoidable water absorption. We then directly identify the optimal sensing condition and track its evolution across the spatially encoded parameter space. The results establish a compact single-chip strategy that combines adsorption-kinetics monitoring, vibrational fingerprint detection, and on-chip optimization, opening opportunities for investigating biological dynamics under aqueous conditions.

physics.optics↗

arXiv2026

Real-time ESR tracking for sub-micron 3D magnetic mapping with VB- quantum sensors in hexagonal boron nitride

The discovery of spin-dependent luminescent properties of negatively charged boron-vacancy centers ($V^-_B$) in hexagonal boron nitride (hBN) enabled a new platform for quantum sensing with van der Waals materials. Particularly, the possibility of performing optically detected magnetic resonance (ODMR) for determining the electron spin resonance (ESR) frequencies of hBN color centers became a strong tool for quantum sensing of magnetic fields with submicrometric resolution. However, due to low ODMR contrast, current techniques proposed for mapping DC magnetic fields require hours of integration to obtain a magnetic image of a micron-sized region. In this work, we report the implementation of a frequency-tracking approach for real-time monitoring of ESR frequencies of localized $V^-_B$ centers in hBN. With this technique, magnetic field monitoring was used to map the field pattern generated by a micron-sized conical magnetic tip in only a few minutes. By controlling the magnetic sample's position relative to the quantum sensor, three-dimensional magnetic mapping of the field was achieved with diffraction-limited resolution and shot-noise-limited sensitivity of 54 $μ$T$/\sqrt{\text{Hz}}$. Magnetic field gradients of 3.6 $\pm$ 0.2 $μ$T/nm were measured with our system, in which a maximum detected field rate of 6 mT/s was achieved. The results of this study establish spin resonance frequency-tracking as a viable technique and fast method for minute-scale magnetic imaging, reducing acquisition times by at least one order of magnitude if compared to conventional techniques.

physics.chem-ph↗

arXiv2026

Enantioselective optical trapping and characterization of all dielectric disorder-enabled chiral particles

We trap submicroscopic silica spheres coated with randomly distributed titanium dioxide nanoparticles in optical tweezers with Laguerre-Gaussian modes and observe orbital dynamics that differ from those of achiral silica spheres. We show that the disordered nanoparticle coating generates an effective chiral geometry, giving rise to enhanced enantioselective chiral optical forces and a measurable modification of the orbital period. A theoretical model based on the Mie-Debye formalism, including optical aberrations, not only quantitatively explains the experimental results but also allows to characterize the Pasteur parameter quantifying the chiroptical response of individual composite particles. These findings constitute direct experimental evidence of chiral optical forces exerted by structured light beams on individual chiral particles and identify disorder-enabled, all-dielectric particles as a versatile material platform to tailor chiral optical forces at the nanoscale.

physics.optics↗

arXiv2026

Rewritable Chirality of Metasurfaces with Permittivity-Asymmetric Flatband Quasi-Bound States in the Continuum

Flatband eigenstates are widely applied to enhance angle-robust light-matter interactions in metaphotonics. However, controlling the polarization of flatbands remains challenging, as it is usually fixed once the metasurface is fabricated, with no options of post-fabrication modification. Here, we present a rewritable permittivity-asymmetric quasi-bound state in the continuum (ε-qBIC) metasurface platform, where selective polymethyl methacrylate (PMMA) coating of a silicon double-nanorod unit cell establishes a circularly polarized flatband state. By varying the PMMA thickness, the polarization of this state can be further controlled in the range from the right-circular to linear and to left-elliptical. The flatbands maintain stable resonance positions and robust far-field polarizations for the incidence angles up to 10 degrees. Importantly, the PMMA layer can be removed, recoated, and re-patterned on the same nanostructure, providing a pathway to rewrite the optical response. Building on this capability, we experimentally demonstrate the chirality encoding by spatially selective PMMA coating. The results establish a practical strategy for realizing high quality factor flatband metasurfaces with rewritable chirality, thus opening opportunities for applications in chiral encoding and chiroptical photonic devices in general.

physics.optics↗

arXiv2026

Absolute Primary Nanothermometry Using Individual Stark Sublevels of Rare-Earth-doped Crystals

We present two independent optical methods for absolute primary thermometry using rare-earth-doped nanoparticles. Both approaches rely exclusively on the internal energy levels and population dynamics of the dopant ions, eliminating the need for external temperature references. We experimentally demonstrate the concepts by using Y$_2$O$_3$: Yb$^{3+}$/Er$^{3+}$ nanoparticles, exploiting Boltzmann distribution between individual Stark sublevels of the Er$^{3+}$ ions, emitting in the green spectral region ($\sim$550 nm) and in the near-infrared spectral region ($\sim$1600 nm). Our strategy establishes rare-earth-based luminescence thermometers as genuine absolute primary probes, conceptually comparable to Johnson noise and acoustic gas thermometers, but with the fundamental advantage of possibly being employed at the nanoscale, potentially down to the single-ion limit, with optical readout and over wide temperature ranges.

physics.chem-ph↗

arXiv2025

Integration of 2D Materials in Radial van der Waals Heterostructure Metasurfaces

Two-dimensional semiconductors, such as monolayer transition metal dichalcogenides (TMDC), exhibit strong excitonic transitions at room temperature and offer a unique platform for exploring light-matter interactions in nanoscale photonic systems. In this work, we demonstrate a compact and polarization-invariant photonic metasurface, fabricated from hexagonal boron-nitride (hBN) and based on radial bound states in the continuum (BIC), which are formed by radially distributed pairs of structurally asymmetric resonators. The metasurface employs multiple symmetry-breaking perturbations to support high quality-(Q-)factor resonances within a footprint smaller than 8 x 8 $μm^2$ - one-sixth of the area of previous approaches. Compared to established hBN metasurface designs, the radial geometry furthermore achieves significantly higher Q-factors with a reduced footprint. By integrating the hBN photonic structure with a WS$_2$ monolayer, we observe enhanced photoluminescence when its resonance is spectrally aligned with the exciton resonance, accompanied by signatures of discrete momentum-space patterns that identify the orbital-angular-momentum-carrying ring eigenmodes. These features persist over a wide range of excitation powers and show minimal linewidth broadening, indicating robust and spatially modulated exciton-photon coupling. This work establishes a scalable approach for generating hybrid photonic-excitonic states with momentum-space structure, offering new opportunities for exciton localization, valley emission, spatially programmable light-matter interaction in two-dimensional material platforms and compact luminescent devices based on 2D material-integrated metasurfaces.

physics.optics↗

arXiv2025

Boltzmann Thermometry at Cryogenic Temperatures Exploiting Stark Sublevels in Er$^{3+}$/Yb$^{3+}$-Codoped Yttrium Oxide Nanoparticles

The development of reliable luminescent nanothermometers for cryogenic applications is essential for advancing quantum technologies, superconducting systems, and other fields that require precise, high-spatial-resolution temperature monitoring. Lanthanide-doped systems are vastly employed to this purpose, and typically perform optimally at or above room temperature when manifold-to-manifold transitions are used. In this work we exploit individual Stark sublevels to demonstrate an optical thermometer based on Er$^{3+}$/Yb$^{3+}$ codoped yttria (Y$_2$O$_3$) nanoparticles that operates effectively across the temperature range from 25 K to 175 K. This is achieved due to the pronounced crystal field environment of the the Y$_2$O$_3$ host matrix, leading to well-separated Stark lines in the luminescence spectrum of the Er$^{3+}$ ions. By applying the Luminescence Intensity Ratio (LIR) method to transitions originating from two Stark components of the $^4$S$_{3/2}$ manifold of the Er$^{3+}$ ions, we achieve thermal sensitivities up to 1.25 % K$^{-1}$ at 100 K and temperature resolutions reaching 0.2 K. Our results further experimentally confirm recently published theoretical predictions, demonstrating that thermometric performance is not directly dependent on the average (barycenter) difference of the involved electronic energy levels when using individual Stark transitions to evaluate the LIR. The proposed procedure gives an energy gap calibration that matches the one determined by sample spectroscopy for non-overlapping lines in the luminescence spectrum. These insights provide a robust foundation for the design of high-performance cryogenic thermometers based on rare-earth-doped materials.

physics.chem-ph↗

arXiv2025

Chiral Nonlinear Polaritonics with van der Waals Metasurfaces

In the strong-coupling regime, the interaction between light and matter reaches a hybridization state where the photonic and material components are inseparably linked. Using tailored states of light to break symmetries in such systems can facilitate the development of novel non-equilibrium quantum materials. Chiral optical cavities offer a promising approach for this, enabling either temporal or spatial symmetry-breaking, both of which are unachievable with conventional mirror cavities. For spatial symmetry-breaking, a cavity must discriminate the handedness of circularly polarized light, a functionality uniquely provided by chiral metamaterials. Here, we propose and demonstrate experimentally a chiral transition metal dichalcogenide (TMDC) metasurface with broken out-of-plane symmetry, allowing for the selective formation of self-hybridized exciton-polaritons with specific handedness. Our metasurface maintains maximal chirality for oblique incidence up to 20°, significantly outperforming all previously known designs, thereby transforming the angle of incidence from a constraint into a new degree of freedom for sub-nanometer-precise tuning of the cavity's resonant wavelength. Moreover, we study the chiral strong-coupling regime in nonlinear experiments and reveal the polariton-driven nature of chiral third-harmonic generation. Our results demonstrate a clear pathway towards van der Waals (vdW) metasurfaces as a novel and potent platform for chiral polaritonics with implications in a wide range of photonics research, such as non-reciprocal photonic devices and valleytronics.

physics.optics↗

arXiv2025

Compact orbital-angular-momentum multiplexing via laser-written glass chips

Orbital angular momentum (OAM) modes have emerged as a promising solution for enhancing the capacity of optical multiplexing systems, leveraging their theoretically unbounded set of orthogonal spatial modes. However, the generation and detection of OAM multiplexing signals are predominantly reliant on bulky optical components within complex optical setups. We introduce a compact solution for OAM information processing using laser-written glass chips, facilitating efficient multiplexing and demultiplexing of multiple OAM information channels. During the multiplexing process, OAM channels are managed via laser-scribed single-mode waveguides within a glass chip, with their modes converted using laser-written holograms on the side wall of the glass chip. The reverse optical process is employed for OAM demultiplexing. Our chips seamlessly interface with commercial optical fibers, ensuring compatibility with existing fiber-optic communication infrastructure. This work not only establishes a novel approach for OAM optical multiplexing but also underscores the potential of laser-writing technology in advancing photonics and its practical applications in optical communications.

physics.optics↗

arXiv2025

Ultrafast all-optical switching in nonlinear 3R-MoS$_2$ van der Waals metasurfaces

Second-order nonlinear optical processes are fundamental to photonics, spectroscopy, and information technologies, with material platforms playing a pivotal role in advancing these applications. Here, we demonstrate the exceptional nonlinear optical properties of the van der Waals crystal 3R-MoS$_2$, a rhombohedral polymorph exhibiting high second-order optical susceptibility ($χ^{(2)}$) and remarkable second-harmonic generation (SHG) capabilities. By designing high quality factor resonances in 3R-MoS$_2$ metasurfaces supporting quasi-bound states in the continuum (qBIC), we first demonstrate SHG efficiency enhancement exceeding 10$^2$. Additionally, by using degenerate pump-probe spectroscopy, we harness the C$_{3v}$ system's symmetry to realize ultrafast SHG polarization switching with near-unity modulation depth. The operation speeds are limited only by the excitation pulse duration, allowing its characterization via the nonlinear autocorrelation function. These findings establish 3R-MoS$_2$ as a transformative platform for nanoscale nonlinear optics, offering large conversion efficiencies and ultrafast response times for advanced pulse measurement devices, integrated photonics, and quantum technologies.

physics.optics↗

arXiv2025

Fabrication Optimization of van der Waals Metasurfaces: Inverse Patterning Boosts Resonance Quality Factor

Van der Waals (vdW) materials have garnered growing interest for use as nanophotonic building blocks that offer precise control over light-matter interaction at the nanoscale, such as optical metasurfaces hosting sharp quasi-bound states in the continuum resonances. However, traditional fabrication strategies often rely on lift-off processes, which inherently introduce imperfections in resonator shape and size distribution, ultimately limiting the resonance performance. Here, an optimized fabrication approach for vdW-metasurfaces is presented that implements inverse patterning of the etching mask, resulting in increased resonator quality solely limited by the resolution of the electron beam lithography resist and etching. Applying this inverse fabrication technique on hexagonal boron nitride (hBN), quality (Q) factors exceeding $10^3$ in the visible spectral range were demonstrated, significantly surpassing previous results shown by lift-off fabricated structures. Additionally, the platforms potential as a biosensor was displayed, achieving competitive sensitivity and figure of merit of 220 in a refractive index sensing experiment. The inverse technique was applied to create chiral metasurfaces from hBN, using a two-height resonator geometry to achieve up to 50 % transmittance selectivity. This inverse lithography technique paves the way towards high-performances vdW-devices with high-Q resonances, establishing hBN as a cornerstone for next-generation nanophotonic and optoelectronic devices.

physics.optics↗

arXiv2025

Addressing Discrepancies Between Theory and Experiments in Boltzmann Luminescence Thermometry with Ln3+ Ions

Trivalent lanthanide ion-doped nanoparticles are widely employed as nanoscale thermometers, driving rapid advancements in real-world applications. When the Luminescence Intensity Ratio (LIR) technique is used, these thermometric systems typically require a calibration process to obtain macroscopic calibration parameters. However, despite extensive studies from various research groups, significant discrepancies are observed among the reported values, even for identical Ln$^{3+}$-host systems under similar experimental conditions. Also, in many cases, the obtained calibration parameters substantially differ from their microscopic counterparts, which is commonly ignored in the literature. This study addresses some sources for these inconsistencies by providing fundamental theoretical insights into the measurement process. We demonstrate that the thermalization of the electronic population within the Stark sublevels of a given manifold plays a crucial role in the LIR's temperature dependence and consequently in measuring the macroscopic parameters. As a result, attempts to construct primary thermometers without prior calibration can result in temperature measurement errors exceeding 20 K. Additionally, we show that pathways disrupting Boltzmann thermalization, influenced by experimental conditions, also affect the evaluation of the macroscopic quantities. These findings contribute to a more robust theoretical framework for interpreting and understanding ratiometric Boltzmann luminescence thermometry experiments, also paving the way for developing more accurate and reliable primary thermometers.

physics.chem-ph↗

arXiv2025

Temporally symmetry-broken metasurfaces for ultrafast resonance creation and annihilation

Active metasurfaces, compact platforms for nanoscale light manipulation, are transforming technologies like holography, quantum cryptography, and optical computing. Despite their versatility, tunability in metasurfaces has mainly relied on shifting the resonance wavelength or increasing material losses to spectrally detune or quench resonant modes, respectively. However, both methods face fundamental limitations, such as limited Q-factor and near-field enhancement control and the inability to achieve resonance on/off switching by completely coupling and decoupling the mode from the far-field. Here, we demonstrate temporal symmetry-breaking in metasurfaces via ultrafast optical pumping, marking the first experimental realization of radiative loss-driven resonance creation, annihilation, broadening, and sharpening. We introduce restored symmetry-protected bound states in the continuum as a new concept which are central to the realization of temporal symmetry-breaking. These states arise in metasurfaces with geometrically asymmetric unit cells, where the total dipole moment, composed of two antisymmetric dipoles, cancels out. Mie-resonant optical absorption within specific regions of the unit cell locally modifies the refractive index, disrupting the balance between the two dipole moments. A total dipole moment is thereby created or annihilated, and consequently, the radiative loss is tuned. This enables full control over coupling to incoming light, allowing precise adjustment of the resonance linewidth, near-field enhancement, and resonance amplitude. Our work establishes radiative loss-based active metasurfaces with potential applications ranging from high-speed optical and quantum communications to time-crystals and photonic circuits.

physics.optics↗

arXiv2024

Van der Waals heterostructure metasurfaces: atomic-layer assembly of ultrathin optical cavities

Photonics has been revolutionized by breakthroughs in optical metasurfaces and layered two-dimensional materials. Yet, integrating these two fields in a singular system has remained challenging. Here, we introduce the concept of van der Waals (vdW) heterostructure metasurfaces, where ultrathin multilayer vdW material stacks are shaped into precisely engineered resonant nanostructures for boosting light-matter interactions. By leveraging quasi-bound states in the continuum to create intrinsic cavities from WS$_2$ monolayers encapsulated in hexagonal boron nitride, we observe room-temperature strong coupling and polaritonic luminescence, which further unveils a saturation of the strong-coupling regime at ultralow fluences <1 nJ/cm2, more than three orders of magnitude smaller than in previous 2D-cavity systems. Our approach, seamlessly merging metasurfaces and vdW materials, unlocks new avenues for ultrathin optical devices with atomic-scale precision and control.

physics.optics↗

arXiv2024

Coherent Acoustic Phonons in Plasmonic Nanoparticles: Elastic Properties and Dissipation at Low Temperatures

We studied the frequency and quality factor of mechanical plasmonic nanoresonators as a function of temperature, ranging from ambient to 4 K. Our investigation focused on individual gold nanorods and nanodisks of various sizes. We observed that oscillation frequencies increase linearly as temperature decreases until saturation is reached at cryogenic temperatures. This behavior is explained by the temperature dependence of the elastic modulus, with a Debye temperature compatible with reported bulk values for gold. To describe the behavior of the quality factor, we developed a model considering the nanostructures as anelastic solids, identifying a dissipation peak around 150 K due to a thermally activated process, likely of the Niblett-Wilks mechanism type. Importantly, our findings suggest that external dissipation factors are more critical to improving quality factors than internal friction, which can be increased by modifying the nanoresonator's environment. Our results enable the design of structures with high vibration frequencies and quality factors by effectively controlling external losses.

physics.optics↗

arXiv2024

Si Metasurface Supporting Multiple Quasi-BICs for Degenerate Four-Wave Mixing

Dielectric metasurfaces supporting quasi-bound states in the continuum (qBICs) enable high field enhancement with narrow-linewidth resonances in the visible and near-infrared ranges. The resonance emerges when distorting the meta-atom's geometry away from a symmetry-protected BIC condition and, usually, a given design can sustain one or two of these states. In this work, we introduce a silicon-on-silica metasurface that simultaneously supports up to four qBIC resonances in the near-infrared region. This is achieved by combining multiple symmetry-breaking distortions on an elliptical cylinder array. By pumping two of these resonances, the nonlinear process of degenerate four-wave mixing is experimentally realized. By comparing the nonlinear response with that of an unpatterned silicon film, the near-field enhancement inside the nanostructured dielectric is revealed. The presented results demonstrate independent geometric control of multiple qBICs and their interaction trough wave mixing processes, opening new research pathways in nanophotonics, with potential applications in information multiplexing, multi-wavelength sensing and nonlinear imaging.

physics.optics↗

arXiv2024

Emergent resonances in a thin film tailored by optically-induced small permittivity asymmetries

Resonances are usually associated with finite systems - the vibrations of clamped strings in a guitar or the optical modes in a cavity defined by mirrors. In optics, resonances may be induced in infinite continuous media via periodic modulations of their optical properties. Here we demonstrate that periodic modulations of the permittivity of a featureless thin film can also act as a symmetry breaking mechanism, allowing the excitation of photonic $\textit{quasi}$-bound states in the continuum ($\textit{q}$BICs). By interfering two ultrashort laser pulses in the unbounded film, transient resonances can be tailored through different parameters of the pump beams. We show that the system offers resonances tunable in wavelength and quality-factor, and spectrally selective enhancement of third harmonic generation. Due to a fast decay of the permittivity asymmetry, we observe ultrafast dynamics, enabling time-selective near-field enhancement with picosecond precision. Optically-induced permittivity asymmetries may be exploited in on-demand weak to ultrastrong light-matter interaction regimes and light manipulation at dynamically chosen wavelengths in lithography-free metasurfaces.

physics.optics↗