This PDF file contains the front matter associated with SPIE Proceedings Volume 12991, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

We present an overview of our latest investigation regarding microwave Electromagnetic Jet (EMJ) dedicated to detection, imaging and characterization applications. First EMJ proposed is a parallel plate waveguide loaded with Teflon and terminated with both single and dual elliptically shaped tips. The experimental result shows the generation, respectively, of a single or a double EMJ as numerically expected. To simplify the manufacture of the tips, a rectangular tip replaced the elliptical termination. The numerical results demonstrated an increase in intensity and low FWHM of the beam, especially when using a multi-rectangular section of the tip. Furthermore, a rectangular waveguide with a rectangular tip was also introduced as an alternative to produce the EMJ in two transverse directions. Finally, to obtain a rotationally symmetrical jet, a horn antenna loaded with Teflon and ended with a cylindrical Teflon shape was proposed. In term of application, the developed microwave electromagnetic jet demonstrates the capability to detect extremely small objects not detectable by conventional microwave systems. In addition, at the focal point, the jet exhibits an almost planar wavefront, indicating the possibility of using the jet for local characterization applications in mesoscale free space measurements.

Over the past few years, the optics and photonics field has faced a challenge in developing the capability to produce structured light with arbitrary controlled polarization in a compact optical path. Our research addresses this challenge by presenting a novel approach involving the design of dielectric dual-functional metaoptics. These miniature, high-resolution metaoptics can generate custom elliptical orbital angular momentum beams with varied behaviors based on the input light's polarization. Our approach enhances the compactness of optical paths and facilitates seamless integration with other optical elements. Specifically, the proposed metaoptics exhibit suitability for applications in particle manipulation, microscopy, high-capacity communications, and security by contributing to complex structured light generation.

Photonic hooks, akin to curved photonic nanojets, result from introducing asymmetry in refractive index distribution, achieved by using asymmetric particles or masking the illumination path. These structures function similarly to Airy beams, enabling particle manipulation and imaging. We propose a planar photonic chip design generating subwavelength-width photonic hooks. Illuminating three Si₃N₄ micro-pillars with a 532 nm TE polarized plane wave—comprising one λ-wide and two λ/3-wide—produces intense photonic hooks above the micro-pillars, with a 0.7 λ FWHM. The larger pillar, separated by 2λ from the smaller ones, which are λ/3 apart, influences hook properties and optical forces. This offers potential advancements in nanophotonics and microfluidic systems integration.

Recent advances in optical trapping have opened new opportunities for manipulating micro and nanoparticles, establishing Optical Tweezers (OT) as a powerful tool for single-cell analysis. Furthermore, intelligent systems have been developed to characterize these particles, as information about their size and composition can be extracted from the scattered radiation signal. In this manuscript, we aim to explore the potential of optical tweezers for the characterization of sub-micron size variations in microparticles. We devised a case study, aiming to assess the limits of the size discrimination ability of an optical tweezer system, using transparent 4.8 μm PMMA particles, functionalized with streptavidin. We focused on the heavily studied streptavidin-biotin system, with streptavidin-functionalized PMMA particles targeting biotinylated bovine serum albumin. This binding process results in an added molecular layer to the particle’s surface, increasing its radius by approximately 7 nm. An automatic OT system was used to trap the particles and acquire their forward-scattered signals. Then, the signals’ frequency components were analyzed using the power spectral density method followed by a dimensionality reduction via the Uniform Manifold Approximation and Projection algorithm. Finally, a Random Forest Classifier achieved a mean accuracy of 94% for the distinction of particles with or without the added molecular layer. Our findings demonstrate the ability of our technique to discriminate between particles that are or are not bound to the biotin protein, by detecting nanoscale changes in the size of the microparticles. This indicates the possibility of coupling shape-changing bioaffinity tools (such as APTMERS, Molecular Imprinted Polymers, or antibodies) with optical trapping systems to enable optical tweezers with analytical capability.

Optical trapping and sensing platforms based on plasmonics were developed due to the desire to both trap and manipulate ever smaller particles using noninvasive optical techniques. Through careful engineering of the plasmonic structures, a Fano resonance can yield a surprisingly large improvement to the trapping efficiency for nanoparticles. Using a split ring array, we have demonstrated trapping of particles as small as 10 nm and have exploited the SIBA effect to improve the trap stiffness for gold nanoparticles. We have extended the technique to sense and determine the phase of E-coli bacteria and have explored thermal effects which can contribute to the trapping processes. Here, we discuss characterization of the devices themselves, to engineer them for specific applications such as enhanced photoluminescence from nano-emitters, particularly nanographenes.

Acoustic interface states have been evidenced in superlattices with frequencies at tens to hundreds of GHz. A recently demonstrated scheme to generate interface states in one-dimensional superlattices is based on the principle of band inversion, obtained by concatenating two periodic lattices with inverted spatial mode symmetries around the bandgap. Most of the realizations exploit a given bandgap for which there is one symmetry inversion. In this work, we present high-order topological nanophononic interface states in multilayered structures, achieved by concatenating two superlattices with different bandgap orders centered around the same frequency. In this case, inverted mode symmetries are not required to achieve the interface state, which is enabled by modifying the unit cells of the two superlattices. We showcase designs for versatile topological devices where interface states can be simultaneously created across a wide frequency range. The topological modes can be experimentally accessed in Brillouin or pump-probe experiments. The ability to explore higher bandgap order acoustic interface states in the GHz range is unique in nanophononic superlattices due to the linear dispersion relation of acoustic phonons. The demonstrated systems can thus be exploited to investigate schemes that are difficult or impossible to study in electronics or optics, due to their non-linear dispersion relations.

Ligand-protected metal nanoclusters (NCs) have emerged as prospective less-toxic luminescent materials which can be beneficial for numerous applications, such as bioimaging, biosensing, photo-induced catalytic process, and optoelectronics. The most intriguing properties of NCs are long photoluminescence (PL) lifetime with broadband PL emission, making them more attractive to be developed. However, low PL Quantum Yield (PLQY) and unclear excitonic dynamics mechanism strongly hinder their practical utilization in daily basis. Therefore, to address these issues, gold-doped silver nanoclusters were synthesized using one-pot synthesis method, and were covalently bonded in a solid matrix, polyvinylpyrrolidone (PVP). The fabricated gold-doped silver nanoclusters embedded in PVP matrix (AuAgNCs@PVP) have bright red emission centered at approximately 650 nm with microseconds PL lifetime. By probing the nanosecond time resolution, it was revealed that two distinct decay profile (nano- and micro-seconds) exist in AuAgNCs@PVP, showing the occurrence of Thermally Activated Delayed Fluorescence (TADF). We also found that after the absorption of photons, thermal equilibrium between singlet and triplet states were quickly reached due to fast intersystem crossing and reverse intersystem crossing (ISC/RISC) process owing to the small singlet triplet energy splitting. Hence, we proposed the mechanism behind broadband PL emission with long PL lifetime was due to Thermally Equilibrated Delayed Fluorescence (TEDF).

Nanoparticle on Mirror (NPoM) plasmonic cavity can be utilized to enhance the spontaneous decay rate of a quantum emitter to a great extent. Here, we calculated the Purcell factor of a quantum emitter placed in such a cavity using COMSOL Multiphysics software. We first simulated the extinction cross-section of a nanorod placed on top of a metal film separated by a small gap. Then, we calculated the Purcell factor of a quantum emitter for a varying gap. We observed that the Purcell factor is greatly enhanced when the gap between the nanorod and the metal film is sufficiently low (⪅4 nm).

In this contribution, we report the study of the FRET (Förster Resonance Energy Transfer) effect between AgInS₂ Quantum Dots (QDs) as donor and an organic fluorophore (cyanine 5 – Cy5) as acceptor, with the QD-Cy5 inter-distance d tuned by DNA strands. To this end, the cyanine dye linked to a single-stranded DNA (ssDNA) was first hybridized with its complementary thiolated DNA sequence. The resulting double-stranded DNA (dsDNA) construct was then used to functionalize the QD. The analyses of the optical properties of these nanohybrid assemblies were conducted by fluorescence. We found a characteristic Förster distance R0 = 6 nm for this system with an experimental FRET efficiency of 57 % for a distance d = 6 nm = R0, and 17 % for d = 13 nm ⪆ 2R0 in agreement with the theory. To explore the potential of such assembly for sensing applications based on FRET and DNA hybridization process, we have studied another approach: the QD was first functionalized with thiolated ssDNA single strand, and then the organic fluorophore linked to complementary DNA sequence was added by selective hybridization. Surprisingly, in this second approach, a strong FRET was observed whatever the targeted QD-Cy5 distance (efficiency ⪆70%). We will discuss the reasons for this non-expected effect.

We present a comprehensive study of the elementary dipolar contributions to the absorption and scattering cross sections in chiral, twisted, vertically stacked plasmonic plates that have been proposed as acoustoplasmonic transducers. Using a very basic model system we show scattering and absorption cross sections presenting very large qualitative differences for left-circular and right-circular polarizations. We make use of an expansion in vector-spherical-harmonics multipoles to analyze the different contributions to the cross sections depending on the helicity of the incoming wave. In the analysis of the scattering cross section, we demonstrate that interactions not only modify the spectral dependence of the dipoles representing the elements in the nanostructure, but they affect the cross section itself elucidating the dependence on the helicity of the incoming light beam.

Material anisotropy produces differential absorption and birefringence of linearly polarized light; material chirality leads to differential absorption and birefringence of circularly polarized light. Here we highlight how anisotropic media can produce a differential absorption and birefringence which depends on the sign of the topological charge ℓ of a focused optical vortex beam. Manifesting purely through electric-dipole interactions and proportional to the paraxial parameter to first order, these topological-charge-dependent light-matter interactions are significantly larger than current ℓ-dependent effects which require material chirality and extremely focused light. The interactions described within represent a novel method for probing the local structure of advanced materials and nanoscale light.

Phyllosilicate minerals are an emerging class of naturally occurring layered insulators with large bandgap energy that have gained considerable attention from the scientific community. This class of lamellar materials has been recently explored at the ultrathin two-dimensional level due to their specific mechanical and optoelectronic properties, which are crucial for engineering novel devices (including heterostructures). Due to these properties, phyllosilicate minerals can be considered promising low-cost nanomaterials for future electronics, photonics, and optoelectronics applications. Here, we will provide an overview of nano-optics and local chemistry of various 2D natural phyllosilicates by IR s-SNOM. Also, the relevant features of these layered materials for their use in potential optoelectronic applications will be presented.

Prism-based Surface Plasmon Resonance (SPR) sensor is a powerful label-free analytical technique used in food safety, medical diagnostics, and environmental monitoring. It is currently mainly used in centralized laboratories due to its size and price. Grating-based SPR sensors offer a cost-effective and miniaturized alternative for point-of-care applications. However, grating based SPR sensors have limited performance and robustness for practical use. In this study, we present a high-performance, robust, and compact grating based SPR sensor enabled by a tunable laser working at normal excitation and readout incidence. This configuration eliminates the spectral analysis and moving parts, thereby enhancing the robustness of the instrumentation. The sensor was designed, optimized, and analyzed using COMSOL Multiphysics, and then fabricated through nanoimprinting lithography. Both computationally and experimentally, we demonstrated the SPR dip splitting at non-zero incidence, which was lacking in previously reported grating-based SPR sensor studies. The sensor was tested with glucose solutions, achieving a sensitivity of 1101.6 m/RIU. The figure of merit of the sensor was 229.5 surpassing other reported grating-based SPR sensors by one order of magnitude. The experimental results were in good agreement with the simulations. We also demonstrate its performance in detecting low concentrations of glucose and creatinine with the limit of detection of 14.2 mM and 19.1 mM, respectively. These results show the potential of our high-performance, portable SPR sensor for point-of-care applications.

Here, we apply a novel technique involving Joule-assisted active plasmonics to enhance the sensitivity of the well-established surface plasmon resonance (SPR) method. Typically, SPR curves are generated from an angularly resolved scan of the reflected light beam from a metal thin film – dielectric interface. Due to the sensitivity of Surface Plasmon Polaritons (SPPs), and confinement to the vicinity of the interface, they are an important utility in a variety of applications. In this work, a modified setup involving a heated active plasmonic bridge allows insight into the metal surface characteristics not seen through classical Attenuated Total Reflection (ATR) measurements. Here, a constriction in the metal acts as a microscale bridge which is heated, via the Joule effect, and whose temperature follows the cycle of an alternating current. Employing a lock-in amplifier, referenced to the applied sine wave, enables detection of the reflected light now modulated by the alternating current resulting in a change in the optical constants. This dynamic technique is more sensitive than the conventional ATR technique and hence is capable of detecting metal composition, surface chemistry, and morphology above the active plasmonic element. This has opened the door to enhance already highly sensitive SPR devices currently on the market. In this study, we focus on the phase relationship between the Joule heating of an active plasmonic device and demonstrate that the laser spot alignment is of crucial importance to reach optimal sensitivity.

The capability to actively control the formation of Surface Plasmon Polaritons (SPPs) by means of temperature changes is one of the base working principles for active plasmonic devices, sensors and imaging systems. In order to exploit this idea, it is necessary to have a very in-depth knowledge of the changes induced by heating in the optical properties of plasmonic materials in real operational conditions. Previous studies have tracked the influence of temperature on plasmonic materials’ refractive indices, but data are usually acquired with large temperature steps (≈ 100°C - 300°C), and don’t always focus on extracting a precise relationship between optical constants and temperature in non-ideal environments, assuming the a very high purity of the materials involved and a controlled atmosphere. This research aims to fill the gap in the existing literature by means of a systematic approach, involving both a temperature-controlled Surface Plasmon Resonance (SPR) acquisition setup capable of 1◦C steps and a computational approach to fit data and explain changes in the optical properties. To verify the influence of temperature changes on the localisation of the electric field itself, Finite Element Method (FEM) simulations using COMSOL Multiphysics are conducted. These simulations highlight the differences in systems at different temperatures in terms of electromagnetic field distribution.

In this work, we study lasing in plasmonic nanoparticle arrays with complex structures. Complex structures can be formed by unit cells that contain more than one particle or by creating supercells i.e. giant unit cells, which contain tens of particles. Here, we study lasing in supercell arrays which are based on a square array geometry. The supercell is created by leaving certain lattice sites empty, creating an aperiodic pattern. This supercell is repeated to form an array. We calculate the band structures of the arrays by combining the structure factors of the lattice geometries with an empty lattice approximation. We show that by leaving certain lattice sites empty, some of the destructive interference is removed, leading to additional dispersive branches. This provides new band edges that support lasing. We experimentally demonstrate lasing in such supercell arrays which show interesting lasing emission patterns and multimode lasing.

Recently, novel chiroptical harmonic scattering effects were reported, and the associated techniques have emerged as promising tools for characterizing the chirality of light scatterers, randomly dispersed in isotropic liquids. So far, the associated new physical effects have only been demonstrated in a handful of materials. For each material, only one size distribution has been studied. While third-harmonic chiroptical scattering, in the Rayleigh regime, has previously been demonstrated from Ag nanohelices, the data were only collected for right-handed scattering, with respect to the wavevector of incident light. Here, we present third-harmonic chiroptical scattering from Ag nanohelices with larger dimensions than those studied before. Moreover, we provide data in both right-handed and forward scattering. Our data are consistent with hyper-Rayleigh scattering and demonstrate that the recorded signal follows a cubic law with respect to the illumination laser power. Additionally, the obtained third-harmonic ellipticities clearly distinguish between left- and right-handed Ag nanohelices. The results reported here contribute to establish the applicability of chiroptical harmonic scattering to scatterers with various sizes, randomly dispersed in isotropic liquids.

We demonstrate a metafiber platform capable of creating arbitrarily structured light on the hybrid-order Poincaré sphere. The metasurface is directly printed on the end face of a commercial polarization-maintaining optical fiber through 3D laser nanoprinting process. The release of height degree of freedom greatly expands the 3D meta-atom library, empowering metasurfaces to independently manipulate phase and polarization. Our work provides a paradigm for advancing optical fiber science and technology towards fiber-integrated light shaping, which may find important applications in fiber communications, fiber lasers and sensors, endoscopic imaging, fiber lithography, and lab-on-fiber technology.

Surface-enhanced Raman Spectroscopy (SERS) is a powerful optical sensing technique widely used in fields like medicine, microbiology, and environmental analysis. Planar SERS substrates are preferred for their ease of integration into lab-on-chip systems and superior reproducibility. Substrate performance is assessed using metrics like enhancement factor, sensitivity, and reproducibility. Many experimental and post-processing factors can influence these metrics and their interpretations, with one of the most critical being the illumination area—essentially, the number of hotspots generating the signal. We investigated with Raman mapping the impact of the illumination area on five SERS substrates showing that a larger illumination area improves reproducibility on random structures, while it sacrifices resolution. Furthermore, a larger illumination area leads to more stable signals, particularly in irregular nanostructures, yielding higher sensitivity. In conclusion, choosing a SERS substrate should consider the trade-off between uniformity for resolution and larger illumination area for signal reproducibility.

Gallium is a well-suited material for fabricating flexible photonic devices due to its fluidic and metallic properties. Localized Plasmonic resonance relies on fabricating metallic structures at the nanoscale with an extremely small gap between them, thus employing lithography or self-assembly techniques involving multiple reagents and process steps. In this work, we demonstrate a single-step and scalable fabrication of non-coalescent Ga Nanospheres on a biocompatible elastomeric substrate, Polydimethylsiloxane (PDMS), by exploiting the capillary interactions between liquid Ga and the uncured oligomers of PDMS. This approach enables the fabrication of multiple structural colors and mechanochromic sensors in a single deposition, owing to the active role played by PDMS in determining Ga nanostructures.

The advancement of super-resolution techniques is essential to the progress of cell and molecular biology. This work presents an overview of the fundamentals and development of Plasmonic Electronically Addressable super-Resolution (PEAR) as a novel super-resolution technique. PEAR aims to improve on limitations faced by currently established methods. PEAR uses an active plasmonic element which is modulated by passing an electric current through the nanostructure, this modulated electric current causes changes in the electrical near field at the modulation frequency. Using a homodyne detection scheme, with the modulation frequency as a reference, sub-diffraction limit spatial information can be transferred into the far field. Recording changes in the modulated light levels allows an image of a sample’s surface to be constructed. PEAR offers a unique advantage over established methods. It ties the spatial resolution of the resulting image to the physical size of the active plasmonic element which, in its simplest, form consists of a constriction in a silver thin film, allowing tuning and de-tuning of the plasmonic resonance when heated. Passing an alternating current through the nanostructure causes changes to the surface plasmon resonance condition. Hence, modulating the electric near field localized to the vicinity of the active plasmonic element experiencing Joule heating. While these changes are of the order of a few percent relative to the overall light levels, the encoded modulation allows the use of a lock-in amplifier to extract changes in the light level at the modulation frequency far below the noise floor. As fluorescent material interacts with this modulated electric near-field it will transfer local information into the far-field, which can be collected using standard optics. As the modulation is highly localized to the active plasmonic element, only the area of fluorescent material directly interacting with the active plasmonic element out-couples the light encoded with the modulation frequency. This directly connects the resolution of the imaging technique to the geometry of the active plasmonic element. By scanning a fluorescent sample over the active plasmonic element in a raster fashion, a map of the localized information is compiled to form an image of the sample’s surface. The PEAR method provides a non-destructive, bio-compatible imaging method which is operational in air, with ease of scalability into multi-channel acquisition in order to reduce acquisition time while maintaining signal to noise ratio. Combining these advantages with the ability to tie the resolution to the physical size of the active plasmonic element makes the PEAR imaging method unique among other imaging technologies at the forefront of super-resolution imaging.

Strong light-matter interaction is gaining much interest, particularly in plasmonic systems. Plasmonics offers a suitable platform to utilize strong coupling conveniently due to its ability to confine light to a subwavelength regime. Under a strong coupling regime, new hybrid states are formed that have properties of both light and matter. The properties of the hybrid states are fascinating and are worth investigating. In this study, we report a novel computational method to determine the propagation length of Surface Plasmon Polaritons (SPPs) on a metal-dielectric interface using COMSOL Multiphysics in the Kretschmann configuration. We show that the propagation length of SPPs depends on the wavelength and the imaginary part of the refractive index of the metal on which these plasmons are travelling. We also demonstrate the changes in the propagation length as we enter the strong coupling regime. When a thin gold film is coated with absorber material, it forms hybrid states of SPPs and the absorber material. In these hybrid states, the propagation length changes significantly. The decay of hybrid polariton contains both the properties of SPPs and the absorber material. Our study shows a numerical approach to calculate the propagation length of SPPs. This approach also extends its utility to experimental measurements of the propagation length, particularly in 2D materials like MoS₂.

We have demonstrated that the defective photonic crystal attains exceptional optical properties by doping its defect layer with lambda type three-level atoms. We have incorporated transfer matrix formalism and observed that the crystal behaves as non-PT symmetric one by violating symmetry relations of the corresponding matrix. As a result, we have shown that the two frequency modes lying in the band gap show maximum asymmetry in reflection and absorption at critical coupling, when atom is in resonance with the defect mode which can be coherently controlled while the critical coupling remains robust when crystal is operated at off-resonance.

The miniaturization of semiconductor lasers to the nanoscale is difficult because of increasing losses as the laser cavity size approaches the wavelength of light, with some recent efforts focusing on high-refractive index dielectric materials and plasmonics to try and overcome this challenge. With this in mind, we immobilize CdSe1-xSx/ZnS Colloidal Quantum Dot (CQD) supraparticle (SuP) microlasers onto gold nanoparticle (AuNP) coated glass substrates. We study the interaction of the absorption, the non-resonant luminescence, and the Whispering Gallery Modes (WGMs) of SuPs with the Localized Surface Plasmon Resonances (LSPRs) of a AuNP substrate. This interaction produces an increase in LSPR peak intensity of 10%. The luminescence and the WGM-to-non-resonant-luminescence ratio are both significantly increased (x2) under continuous wave excitation at the LSPR wavelength. Individual SuPs can also still act as microlasers when pulsed optically pumped on AuNPs outside the LSPR at 355 nm. These findings suggest this platform as a candidate for further development towards electrically driven cw optical energy sources, presenting us a solution processable route to device miniaturization.

We present a versatile method to fabricate conical nanopores of different materials and shapes on silicon/silicon nitride chips for various nanoscale applications. We drilled silicon nitride membranes coated with photoresist with Focused Ion Beam (FIB) calibrated to the desired shape, followed by atomic layer deposition of a dielectric oxide and subsequent photoresist removal and annealing. We obtained conical nanopores made of SiO₂ and Al2O₃ on a silicon nitride membrane. We characterized the samples electrically, with Scanning Electron Microscopy (SEM), cross sections and Energy-Dispersive X-ray spectroscopy (EDX). We studied concave, straight, and convex nanopore shapes and measured their ionic current rectification effects, which vary with the nanopore geometry. We supported our experimental findings with numerical simulations based on the Poisson-Nernst-Planck model. With the addition of a metallic layer, we conducted enhanced Raman spectroscopy experiments to confirm the capacity of our structures to perform as tailored plasmonic antennas. Our results confirm the robustness and tunability of this fabrication method to produce conical nanopores of dielectric oxides for a wide range of applications and the potential of controlling the nanopore geometry.

Traditional optical microscopy methods with microscope objectives limit interaction angles with biological samples. Microlasers, particularly those based on Whispering Gallery Mode (WGM) resonators, offer powerful sensing capabilities but face excitation constraints. We present an innovative platform that overcomes these challenges using optically trapped micromirrors on flexible polymeric membranes to enable arbitrary excitation angles for WGM microlasers. This approach allows precise environmental sensing and versatile light delivery and collection within microfluidic chambers. Beyond advancing refractive index sensing, optically trapped micromirrors find applications in advanced imaging and light sheet microscopy, promising conditioned light delivery anywhere in the sample plane when combined with metasurfaces.

Solar energy conversion to green energy production via solar water splitting, imitates photoinduced charge transfer into water or an electrolyte using a photoelectrode. Bandgap limitation affects common semiconductors used as photoelectrodes. From that perspective, interband and nonradiative decay of plasmon resonance facilitates a plasmonic phenomenon with a more comprehensive spectrum performance. This work systematically studies photoelectrochemical current generation using plasmonic Gold Nanoparticles (GNPs) organized in a one-dimensional lattice. Such arrangement of plasmonic GNPs produced photonic effects such as guided mode resonance and grating-coupled surface plasmon resonance, which contributed to superior photoelectrochemical current production than metal bar grating, and random gold nanoparticles. Additionally, a semiconductor layer was deposited over the grating of plasmonic particles to enhance plasmonic charge collection and current generation and extended the UV-limited semiconductor's PEC spectral response bolstered by multiphotonic-plasmonic resonance phenomena. Our research offers a derived approach to enable light harvesting mechanisms for the production of green energy.

The relentless rise of Multidrug-Resistant (MDR) bacteria significantly challenges global health, undermining the effectiveness of traditional antibiotics and demanding prompt development of new antimicrobial strategies. This study investigates the antimicrobial properties of Gamma-Aminobutyric Acid (GABA) silver nanoparticles (GABAAgNPs). GABAAgNPs were synthesized via photoreduction and subsequently characterized using UV-Vis spectroscopy, Transmission Electron Microscopy (TEM), and Zeta potential analysis. Their antimicrobial potential was assessed through a Minimum Inhibitory Concentration (MIC) assay. The photodynamic effect was studied under irradiation at the following wavelengths: 460 +/- 10 nm (2 min), 590 nm +/- 10 nm (2 min), and 660 nm +/- 10 nm for 2, 5, and 10 minutes. Our results demonstrated that GABAAgNPs induced porphyrin formation in E. coli, leading to microbial inhibition, further enhanced through the photodynamic effect. Thus, GABAAgNPs display dual functionality: directly targeting microbes while concurrently acting as photosensitizers in antimicrobial photodynamic inactivation (aPDI).

Photonic nanojets typically require a spherical object onto which a laser beam is illuminated. The presence of the spherical object creates a near-field nanojet where light is emitted in the vicinity of the sphere. We explore the nanojet emanating from various diameters of the spheres and find that two different regimes can be present. In the first regime, the sphere is small when the transverse dimension of the nanojet is smaller than the diffraction limit while the axial dimension is diffraction limited, as has been recently shown. In addition, we find another regime where the sphere diameter is much larger than wavelength, when the axial dimension of the nanojet is now smaller than the diffraction limit keeping the transverse dimension the same as diffraction limit. This yields very high numerical apertures. We also show that we can optically confine particles with a axial corner frequency which is a factor of three larger than regular optical trapping with 100x objective due to the subdiffractive axial nanojet.

We use a rigorous vector Born series to solve electromagnetic scattering by a diffraction grating. To deal with possible divergence of the Born series, we compute Padé approximants of the Born series to retrieve the solution regardless. Besides results of the Born-Padé method for an example grating, for which the Born series diverges, we show analytical expressions for a two-layer grating in the case of s polarization. This gives insight into the convergence behavior of the Born series as function of the angle of incidence, for instance.

In this paper, we present an innovative top-down approach for fabricating billions of InGaN/GaN-based dot-Light-Emitting Diodes (LEDs) that eliminate the need for a sacrificial layer. Our method combines Electrochemical Etching (ECE) and sonochemical separation to isolate the dot-LEDs. Key electrochemical parameters are investigated to assess their impact on the nanopore size, separation efficiency, and the dot-LEDs’ emission properties. Higher voltages result in more extensive electrochemical etching of the n-GaN portion. Furthermore, lower vapor pressures, along with higher viscosities and surface tension, enhance the sonochemical separation efficiency of dot-LEDs during the ECE process. Blue electroluminescent devices fabricated using these dot-LEDs achieved an External Quantum Efficiency (EQE) of 7.34% at a forward voltage of 4.2 V, with remarkable luminance efficacy. Although the current generation of blue Au-coated dot-LEDs does not surpass the EQE of existing displays, it marks a significant step in the burgeoning field of dot-LED display technology.

Quantum Dots (QDs), renowned for their unique electronic and optical properties, are finding innovative applications in areas such as bioimaging, quantum computing, and light-emitting diodes. This study focuses on biconical (QD), which offer enhanced control over charge carrier confinement, leading to greater tunability of their electronic and optical properties. Utilizing numerical discretization within the effective-mass approximation, the research accurately calculates excitonic properties in these complex systems, particularly in GaAs biconical QDs. Additionally, the photoluminescence properties of these biconical QDs show promise as tunable light sources, with the added benefit of electric field influence for photoluminescence. The research also explores the energy dependence on bicone geometry, highlighting energy coincidence as the two cones' heights match. Photoluminescence investigations, conducted on biconical QDs of varying sizes under different electric field conditions, confirm the expected red and blue shifts based on the field direction. In conclusion, this study establishes a theoretical foundation for manipulating the properties of biconical QDs, opening avenues for their application in optoelectronic devices. The ability to control photoluminescence shifts through electric field direction underscores the practical significance of this research.

In this study, we investigated electronic properties of a dumbbell-shaped Quantum Dot (QD) made from gallium arsenide. For this purpose, we employ the finite element method. Our investigation begins by calculating the wave functions and energies of the ground state and the first nine excited states. This allows us to understand how the quantum dot's shape impacts its electronic structure. Based on the obtained results for the wave functions and energies of one electron, we calculated the oscillator strengths for different quantum transitions. We discover that the most pronounced absorption occurs during transitions between the ground state and the second, third, eighth, and ninth excited states. Additionally, we analyzed the absorption processes between these energy levels and revealed the dependence of the absorption coefficient for the intraband transitions dumbbell-shaped QD on the energy of the incident light.

The Goos-Hänchen shift (GHS) can be measured typically by fixing the wavelength of incident light and changing the angle of incidence to analyze the optical modulation characteristics of the film material or its relevant parameters. In this paper, the membrane structure of one-dimensional photonic crystals (1DPC) was analyzed by varying the wavelength of incident light combined with GHS measurements. The theoretical analysis and experimental results show that the spectrum-GHS analysis method can show the band gap of 1DPC well and enhance the GHS, so as to improve the sensitivity of the prism-type sensors with 1DPC film sensitive layer. The abstract summarizes key findings in the paper.

This project explores optical near-field characterizations using a scattering Scanning Nearfield Optical Microscope (s-SNOM) with a monochromatic visible illumination on SiO₂ dielectric thin films, elaborated by electron beam deposition onto Silicon wafers. Although the amplitude and phase resulting from the optical near-field interaction are mostly used for qualitative characterizations, this work aims to achieve direct quantitative measurements of optically transparent components. In parallel, theoretical models of electric field and reflectivity variations in the propagative regime were employed, and the results were compared to the optical near-field signal variations. Insights on the properties of optical components that can be accurately measured with s-SNOM are thus provided.

Stress is a widely spread phenomenon in the modern society. Only work-related stress was estimated to cost US companies more than $300 billion a year in healthcare costs, absences and decreased performance. Early diagnosis of stress conditions and therefore improved recovery and reduced costs could potentially be achieved with continuous monitoring of stress biomarkers using wearable devices. Compared to the conventional electrochemical and optical sensing methods used in current wearable devices, plasmonic sensing could offer higher sensitivity, better stability and faster data collection. Our developed plasmonic sensor chip represents a nanograting structured polymer on a silicon substrate, covered with gold. The sensing method is based on detecting a surface plasmon resonance wavelength shift due to refractive index change caused by presence of analytes in the vicinity of the plasmonic grating. The sensitivity of the chip was tested with two different stress-related biomarkers: cortisol and creatinine. With the tested range from 0 to 265 mM, in the current version of the system, without a receptor layer, the detection limits for cortisol and creatinine were 10.65 and 7.09 mM, respectively, which are close to the physiological ranges of these analytes in body fluids. When integrated into a wearable device, this approach has a potential in future healthcare applications paving the way to continuous stress monitoring.

Vanadium dioxide (VO₂) exhibits reversible insulator-to-metal phase transition at 68°C, making it promising for diverse applications. However, its low thermal stability in the metallic phase and insufficient emissivity in the near-mid infrared range limit practical use. To address these challenges, we propose a core-shell structure deposited on a metal layer. This configuration enhances VO₂'s optical properties in both phases, facilitating efficient absorption and reflection of near-infrared radiation.

This paper presents a comprehensive exploration of Surface-Enhanced Raman Spectroscopy (SERS) substrate design, leveraging Finite-Difference Time-Domain (FDTD) simulations for systematic parameter sweeping. Our investigation goes beyond enhancing SERS performance, addressing the crucial aspect of manufacturability with two-photon polymerization (2PP). By examining parameters such as height, pitch, and diameter, we aim to identify structures that not only exhibit high enhancement factors but also possess higher tolerances suitable for practical fabrication. Novel models are developed to visualize SERS hotspots based on nominal shape and AFM data, providing valuable insights for both substrate performance and manufacturability. This dual-focused strategy, integrating FDTD modeling with 2PP fabrication, offers an understanding for advancing SERS substrate design in both sensitivity and practicality.

Quantum dots represent a particularly intriguing class of materials due to their unique crystalline structure, characterized by the emergence of a substantial internal piezoelectric field, even at low indium concentrations. This distinctive feature renders them versatile for a wide range of applications, including light-emitting diodes spanning from red to ultraviolet wavelengths, solar panels, microcontrollers, and energy generation technologies. This research delves into the exploration of exciton states within cylindrical Gan/In_xGa_1-xN Quantum Dots (QDs). To effectively model the confinement potential of such QDs, the modified Pöschl-Teller potential is employed in the axial direction, while for the radial direction parabolic potential is used. The study initially focuses on assessing the dependence of critical parameters. This includes the wave function, ground, and first excited state energies, as well as binding energies. These dependencies are examined regarding with the geometric characteristics of the quantum dot and the concentration of indium within the material. Of particular interest are the observed effects of varying indium concentrations, which have a profound impact on the internal piezoelectric field, influencing the spatial separation of electron-hole pairs and modulating the band gap curvature. Subsequently, our investigation extends to the analysis of absorption processes, specifically the interband absorption and the creation of the electron hole pair. We scrutinize the intricate relationships between these absorption processes, the geometric properties of the quantum dots, and the indium concentration. In addition, the selection rules have been revealed for the corresponding quantum transitions. In summary, this study provides valuable insights into the excitonic properties of cylindrical GaN/In_xGa_1-xN quantum dot considering taking into account piezoelectric effects arising due to the indium concentrations.

Spatiotemporal Optical Vortices (STOVs) are a type of optical pulse carrying tranverse orbital momentum. Here, we present analytical expressions modeling STOVs that are as round as possible. We obtain those expressions by applying mathematical differential operators to light “blobs” presenting a Poissonian spectrum and modeled with a complex focus method.

To achieve full control over acoustic phonons at ultrahigh frequencies, it is essential to characterize the phonon transport properties. Recent works have shown that surface acoustic waves at gigahertz frequencies can propagate over micrometer distances in different nanostructures such as nanowires, nanogratings, and nanoantennas. Here, we aim at investigating acoustic phonon transport by designing a GaAs/AlAs optophononic waveguide. Along the vertical direction of the waveguide, a Fabry-Perot cavity ensures an efficient confinement of acoustic phonons that has been demonstrated in planar and micropillar structures. In the lateral direction, the interface of air and semiconductor serves as an acoustic mirror to reflect phonons in the waveguide. We perform pump-probe experiments to generate coherent acoustic phonons at one position and detect them remotely on the waveguide. We analyze the signals originated by phonons generated in the pump position reaching the remote probe location, revealing a clear indication of phonon transport at room temperature. Our findings have potential applications in quantum technologies and data processing.

Surface relief gratings are proven to be valuable tools for polarization control, spectral and spatial filtering in the optics and electromagnetics community. With the use of guided mode resonance effect, one can achieve desired reflection/transmission properties of thin film gratings that can be applied in laser resonators as filters that partain lowest order transverse resonator modes, hence them being amplified in the gain medium. Such media can be: solid state laser systems, Vertical Surface Emitting Lasers (VCSELs), semiconductor laser systems, nanolasers, etc. This work mainly focuses on the application of genetic algorithm with Rigorous Coupled Wave Analysis algorithm to solve the inverse design problem for angular filter applications.

We propose a novel design of grating couplers to be used as the building blocks of the optical antennas of Lidar systems, designed in the well-established Si3N4-TriPleX platform, that offers low-loss waveguides and allows the integration of the dispersive grating elements with ultra-low-loss and low-energy photonic beamformer circuits. The grating couplers are based on standard asymmetric double-stripe waveguide geometry and are designed with 100nm spectral range around 1550nm. More specifically, we design non-uniform geometry grating couplers, varying the waveguide width and filling factor, targeting constant effective refractive index across the propagation direction, and thus constant emission angle, while optimizing for a uniform emission profile. The designs allow to achieve low theta angle divergence as well as maximum wavelength steering. The reported design showcases theta angle 3dB divergence of 1o, phi angle 3dB divergence of 20o and wavelength steering of 10 o /100nm. The proposed components show low fabrication complexity and are compatible with standard fabrication processes. A comparison between uniform and non-uniform grating designs is also presented, investigating also their performance in an OPA configuration. The described methodology is based on mode solving simulations (Lumerical FDE) and propagation simulations (Lumerical FDTD), while the OPA profile extraction is performed with Matlab Sensor Array Analyzer Toolbox.

Accessing acoustic phonons at high frequencies in nanostructures becomes more and more essential in nanoelectronics, nano- and opto-mechanics and quantum technologies, as phonons can strongly interact with electrons and photons at the nanoscale. In spontaneous Brillouin scattering processes, the scattered photons energy, direction and polarization are constrained by selection rules for a given input state. These selection rules are usually considered as intrinsic material properties in crystalline solids and the polarization of the scattered photons depends on the polarization of the excitation. In this work, we use elliptical optophononic micropillar resonators to control these optical polarization selection rules. The degeneracy of the optical cavity modes of circular micropillars is lifted due to the elliptical cross-section of the micropillars, leading to two cavity modes orthogonally polarized and split in energy. The optical field polarization state will depend on both orthogonal cavity modes and their associated polarization states. Therefore, an incident laser beam linearly polarized along the diagonal axis of the elliptical pillar undergoes a wavelength dependent polarization rotation. By choosing the polarization and wavelength of the incident laser, we demonstrate that the polarization state of the incident and reflected laser and the Brillouin scattering signal are different. In this way, background-free spontaneous Brillouin scattering spectra can be efficiently measured in a cross-polarization scheme down to 18 GHz. Here, we theoretically and experimentally explore the optimal conditions for the polarization and wavelength of the incident laser, and the ellipticity of the micropillars, to improve the polarization-based filtering applied to Brillouin spectroscopy.

Fundamental studies of the interaction of chiral light with chiral matter are important, especially for the development of methods that allow selective optical detection of chiral organic molecules. One approach to achieve this goal is to develop a Fabry-Perot resonator that supports eigenmodes with desired electromagnetic handedness which interact differently with the left and right molecular enantiomers. In this study, we theoretically investigate chiral Fabry-Perot resonators with mirrors formed by one-dimensional photonic crystal slabs. We show that the electromagnetic field of the eigenmodes of such resonator can reach the maximum chirality and the intensity distribution is homogeneous without zeros. The one-dimensional photonic crystal mirrors of such a Fabry-Perot resonator have a much simpler geometry than existing solutions, and the rotational degree of freedom allows for fine tuning.

Plasmonic structures, driven by collective electron oscillations in metallic nanostructures, are vital in nanophotonics for manipulating light at the nanoscale. This study focuses on metal nanogaps of 20 nm fabricated via Photolithography and atomic layer deposition, exhibiting tunable transmission resonances across visible to near-infrared wavelengths. Raman spectroscopy of Poly (p-phenylene vinylene) (PPV) on these metal nanogaps reveals altered Raman linewidths without significant changes in Raman frequencies, elucidating the intricate interplay between plasmonics and molecular interactions. These findings are pivotal for advancing our understanding of plasmonic effects at the molecular level, offering insights for innovative optoelectronic device design and sensing applications.

Bragg-Grating-Waveguide (BGW) delay lines are commonly used in transmission mode, owing to the significant elevation in group index observed at the edge of the stopband. However, achieving delays often necessitates structures with a larger footprint, such as cascaded or spiral designs, which consume a substantial amount of chip estate. Recent approaches to optimize chip space involve round-trip configurations with reflectors, but these can restrict bandwidth and cause mode conversion. Our study introduces an efficient solution: a meta-reflector for TE0 mode, enabling double delays via a single path, while also employing a step taper in TM0 mode to couple the TM signal into a strip waveguide, within a 1.9 × 2.6 μm2 area. Simulations show that in TE mode, there is a peak attenuation of -0.18 dB within the 1530–1590 nm wavelength spectrum, and in TM mode, the loss reaches -4.73 dB across the 1500–1600 nm band. In the computation of losses, the customary impact of the Bragg grating waveguide was disregarded, with attention concentrated exclusively on the design of the reflector.

We experimentally demonstrate large arrays of coupled whispering gallery resonators formed by droplets. Employing a fluorescent mapping technique, we measure the spatial and spectral distribution of light intensity across the modes that populate this cavity ensemble.

Integrated Optical Phased Arrays (OPAs) are important for various applications such as LIDAR, microscopy, wireless communication, and holography. Traditional one-dimensional N-element OPAs with individual phase shifters for varied steering angles often have emitter spacings that exceed half a wavelength, leading to grating lobes. Moreover, using true-time-delay lines with varied numbers of periods for different delays may cause amplitude inconsistencies and further side lobe elevation. The proposed Partially Apodised (PA) one-dimensional grating waveguide design controls amplitude while conserving the time delay for targeted steering angles, using distributions as Uniform to minimize grating and side lobes. We fabricated a four-element array with insertion losses of -3 dB for the PA version across the 1530-1580 nm wavelength band.

Quantitative Phase Imaging (QPI) enables non-destructive, real-time, label-free imaging of transparent specimens and can reveal information about their fundamental properties such as cell size and morphology, mass density, particle dynamics, and cellular fluctuations. Development of high-performance and low-cost quantitative phase imaging systems is thus required in many fields, including for on-site biomedical imaging and industrial inspection. Here, we propose an ultra-compact, highly stable interferometer based on a single-layer dielectric metasurface for common path off-axis digital holography, and experimentally demonstrate quantitative phase imaging. The interferometric imaging system leveraging an ultrathin multifunctional metasurface captures image plane holograms in a single shot and provides quantitative phase information of the test samples for extraction of its physical properties. With the benefits of planar engineering and high integrability, the proposed metasurface-based method establishes a stable miniaturized QPI system for reliable and cost-effective point-of-care devices, live cell imaging, three-dimensional topography, and edge detection for optical computing.

A topologically optimized photonic cavity with an integrated lateral p-i-n structure-based silicon (Si) photodetector has been fabricated. The silicon-based cavity allows for the integration of Photodetectors (PDs) in CMOS technology, bypassing challenges associated with adding other materials. The goal of the topological optimization is to maximize the rate of two-photon absorption in silicon, while maintaining small dimensions. The fabricated device was characterized, obtaining a resonant wavelength at 1543 nm with a Q-factor of 6315 and a responsivity of 0.21 mA/W while maintaining a low dark current.

2D materials are compatible with many material platforms as they adhere to other materials strictly by van der Waals interactions. This, together with the variety of band gaps found among Transition Metal Dichalcogenides (TMDCs), makes them uniquely interesting to study for on-chip light sources, as the Photonic Integrated Circuit (PIC) industry is developing into several material platforms depending on the application (gold, silicon, silicon nitride, indium phosphide, etc). 2D materials could thus potentially provide a universal on-chip light source (and detector) scheme for all PIC platforms in the future. Here we show recent results on how exfoliated monolayer TMDC flakes can be integrated with plasmonic slot-waveguides and plasmonic dipole antenna couplers to inject their photoluminescence into plasmonic waveguides as a first step towards future on-chip light sources for such systems.

The search for nano-scaled light sources and detectors, with an emission/absorption precisely controlled through the design of their morphology and structure, is fundamental for developing new synthesis and fabrication solutions in optoelectronics. In this context, a core-shell heterostructure with promising applications in telecommunications serves as an example to demonstrate the technical capabilities available at the hard x-ray nanoprobe beamline ID16B of the European Synchrotron Radiation Facility (ESRF) for characterizing optically active nanomaterials. The proposed case study focuses on an InGaAs/InP Multi-Quantum Well (MQW) structure grown with a perfectly hexagonal shape onto InP Nanowires (NWs). Nano-characterization, using a combination of X-Ray Fluorescence (XRF), X-ray Near Edge Spectroscopy (XANES), and X-ray Excited Optical Luminescence (XEOL) techniques, was conducted to locally probe the elemental homogeneity at the deep submicrometric scale and investigate the local optical properties and their correlations with the phase structure and defects.

Nitrogen Vacancy (NV) centres in nanodiamonds (NDs) are excellent fluorophores. They find applications in bio-sensing, bio-imaging and as single photon emitters. The photoluminescence (PL) spectra of NV centres span over the visible-near IR region (500-900 nm). The spectra consist of temperature-dependent sharp characteristic peaks of neutral and negatively charged NV centres corresponding to Zero Phonon Line (ZPL) transition. When these NV centres are coupled with microcavities, sharp ripple-like resonant modes known as Whispering Gallery Modes (WGMs) are observed in the emission spectra. The time-resolved fluorescence of NV centres are found to be dependent on excitation and emission energies. The fluorescence decay of NV centres reveals the contribution of different charge states. In addition, jet-like structures (photonic nanojet, PNJs) are observed due to the non-resonant interaction of light and NV centre-coupled microcavity. The PNJs have been used to enhance the weak Raman scattering signal.

The manipulation of ultra-high-frequency acoustic phonons in the tens of gigahertz to sub-terahertz range offers a promising avenue for technological advancements. This control can be achieved by means of semiconductor superlattices, such as GaAs/AlAs, which requires costly fabrication processes in order to achieve atomically flat interfaces to avoid phonon scattering and dephasing. In addition, acoustic resonators based on such systems are bound to fixed frequency operations. Mesoporous materials, with pores at the nanoscale, are good candidates to overcome such limitations. It has been shown that multilayered resonators based on mesoporous SiO₂ and TiO₂ support acoustic resonances in the 5-100 GHz range. These materials are susceptible to liquids and vapors infiltration into the pores, causing the modification of the effective optical and elastic parameters. Here we present a design of open-cavity acoustic resonators of SiO₂ Mesoporous Thin Films (MTFs) responsive to the environment. The resonator is composed of an acoustic distributed Bragg reflector, to avoid phonon diffusion towards the substrate, followed by a nickel acousto-optical transducer, and the MTF on top. We characterize the resonator by using coherent phonon generation and detection experiments in a reflectivity pump-probe setup and compare it with a simplified structure. The experimental results show that the acoustic signals in the open-cavity resonator have improved performance. Our findings unveil a promising platform for nanoacoustic reconfigurable optoacoustic devices based on soft, inexpensive fabrication methods. As a perspective to this work, we aim at studying the dependence of the acoustic resonances on the environment humidity.

Hyperuniform disordered photonic materials offer a novel setting for the study of electromagnetic wave propagation in disordered media. They have been shown to have large and complete photonic band gaps in two-dimensions, which have proved useful for arbitrarily shaped waveguides, enhanced solar absorption, and high-Q optical cavities. Investigation of one-dimensional stealthy hyperuniform disordered (SHD) photonic structures remains sparse. Therefore, further exploration is owed to the propagation of electromagnetic waves in one-dimensional SHD photonic structures, and to the geometric properties of the SHD patterns underlying them. In this work, we have generated one-dimensional SHD point patterns using a potential minimisation technique. Through plane-wave expansion simulation of one-dimensional SHD photonic structures, we found that the formation of photonic band gaps requires inclusion of a softcore repulsion term in the potential used to generate the SHD patterns. This repulsion set a minimum displacement between adjacent points and enables the prevention of overlapping scattering elements in the SHD photonic structure. This is in contrast to the case of two-dimensional SHD photonic structures in which large photonic band gaps are present in the absence of a softcore repulsion. With the introduction of a softcore repulsion, we were able to observe examples of photonic band gaps of 21.6% in one-dimensional SHD photonic structures based on Silicon and air. However, the mechanism behind band gap formation is thought to be the onset of medium to long range order. Finally, we present preliminary study of the localisation of electromagnetic waves in one-dimensional SHD photonic structures using both inverse participation ratio and level spacing statistics approaches.

The paper aims to reveal the relationship between the geometrical features and linear and nonlinear optical properties of InAs Quantum Dots (QDs). This problem is justified by the extreme variety offered by the recent advances in growth techniques tailored to attainment of QDs and nanostructures with virtually any shape. To that end the Finite Element Method in conjunction with the Effective Mass Approximation and Envelope Function Approximation was employed allowing the solution of the one particle eigenproblems in domains with any complex geometries. The paper explores nanoplatelets, spherical QDs, nanocones, nanorods, nanotadpoles and nanostars. It has been found that there is a clear correlation between the complexity and symmetry of the QDs and their linear and nonlinear absorption spectra for transitions between the electronic ground state and first three excited states.

Efficient and high-speed photodetection in the NIR is essential in several applications such as LiDAR and imaging. Silicon is an established choice as the base material for absorbing and converting photons to charge carriers. However, its high absorption length in the NIR imposes a trade-off between the absorption efficiency and detection bandwidth. Here, the rigorous coupled-wave analysis method together with the particle swarm optimization algorithm has been employed to optimize photonic crystal slab architectures with hexagonal symmetry to achieve efficient coupling of incoming pulses of light to the guided modes of the silicon photodetector. Our optimal design yields an ultra-efficient compact photodetector with more than 80% average absorption in the wavelength range 700 – 900 nm. Furthermore, considering scatterers of arbitrarily shaped polygonal cross-section, augments significantly the landscape in the optimization parameter space and results in further enhancement of the absorption efficiency. Our results show that introducing different length scales in the texturing leads to efficient broadband absorption in the compact device.

This study explores oxide passivation in Photoelectrochemical (PEC) electrodes featuring nanostructures. The introduction of nanostructures offers the advantage of improved light absorption, but also introduces challenges such as surface defects and hydrophobic surface properties. Oxide passivation provides a simple solution to these problems by offering a variety of material options. However, the high bandgap nature of plain oxides requires thickness optimization due to their dual role as passivation and insulating layers. Among various materials, TiO₂ was selected for passivation of nanoporous silicon photocathode electrodes due to its relatively narrow bandgap and conduction band position, which closely matches the hydrogen evolution potential. In this study, we meticulously analyzed the PEC property changes induced by varying the thickness in steps of 0.5 nm, with the goal of identifying the optimal thickness for improved PEC performance. The results conclusively demonstrate that a 1.5 nm thick direct tunnelable oxide layer provides the best PEC performance. By applying a 1.5 nm thin nanolayer for passivation, a 1.6-fold improvement in photocurrent characteristics compared to Black Si was observed at -1.23 V relative to RHE. Deposition of TiO₂ not only increased the photocurrent but also enhanced the photovoltage up to 110 mV, resulting in an overall positive shift in the electrode potential that is favorable for HER applications. This study highlights the importance of fine-tuning the oxide layer thickness to optimize the performance of PEC systems and highlights the potential of TiO₂ passivation in overcoming limitations posed by the unique properties of nanostructured electrodes.

Gradient-based topology optimization via the adjoint method has been successfully used in nanophotonics to uncover shapes with superior performances compared to what would be possible with traditional design methods. Here, we have used this technique to optimize a dielectric object to engineer its induced multipole moments. As an example, we show the method's application to realize the first Kerker effect in a silicon nanoparticle. The final result shows a rather complex shape with highly suppressed backscattering due to the excitation of in-phase electric and magnetic dipoles with the same amplitude. This promising approach can pave the way for the inverse design of photonic structures based on a set of desired multipole moments, which can exhibit a variety of complex photonic phenomena.

Moths are commonly the target of visual predators such as birds, and hence have evolved some of the most sophisticated of animal pigment patterns. Moths employ coloration for visual misdirection, deterrents, and camouflage, as well as for sexual recognition. Recently, we discovered that all might not be as it seems to human eyes. Noting that both birds and moths have been shown to perceive UV wavelengths, we assessed the coloration of moths under UV lamp light. Under UV lamp light the coloration of some moth species changes. Here, we show that the wings of Jersey Tiger (Euplagia quadripunctaria) moths exhibit fluorescence, a phenomenon observed for the first time in this species. Both the white and red scales of these moths display fluorescence. While UV lamp illumination prompts similar emissions from both white and red scales, 405 nm laser illumination reveals distinct fluorescence spectra. Despite no apparent structural differences observed under SEM between the white, black, and red scales, fluorescence emanates from the entire nanostructured architecture of the scales, indicating a chemical presence throughout. Chemical disparities between the scales are detected via FTIR, though identifying the specific pigment proves elusive. Further investigation is necessary to ascertain the pigments responsible for fluorescence. Additionally, this study prompts exploration of fluorescence patterns in other moth species. The biological significance of this fluorescence phenomenon warrants further inquiry.

We experimentally demonstrate a new type of level crossing where resonances accompany each other along broad spectral bands. Beyond extending the known types of level crossing (simple, avoided, and diabolic), our accompanying levels might transform current supercontinuum-generation technology to be continuous in frequency and time [cw].

The amplification and phase modulation of a surface electromagnetic wave propagating along a helical trajectory in a cylindrical semiconductor waveguide under the condition of phase matching with a longitudinal space-charge wave are considered. The evolution of a phase-modulated wave after passing through a semiconductor waveguide is studied and the conditions leading to the transformation of an initially stationary wave into a sequence of optical pulses with a terahertz repetition rate are determined.

The possibility of strong modification of the reflection spectrum in the photonic bandgap range of a one-dimensional photonic crystal using a dilute two-dimensional array (monolayer) of metal nanoparticles is demonstrated. It is shown that the reflection of electromagnetic wave can be completely suppressed by nanoparticles located in the surface dielectric layer. The dependence of the absorption and reflection spectra of hybrid photonic structure on the array parameters and on the shape of nanoparticles is studied. The obtained results can be used to create filters, polarizers and absorbers for predetermined frequencies in the visible and near-IR domains.

Optical vortex (OV) beams characterized by their twisted wave phase and the Orbital Angular Momentum (OAM) have garnered significant interest and found practical utility in diverse applications like optical communication, particle manipulation, and many more. The topological charge plays a crucial role in defining and recognizing the OV beams, which are controlled by the number of twisted waves and the radius of the intensity profile. The reliance of OV beams on the topological charge poses limitations in numerous applications that necessitate coupling and higher topological charge values. The perfect vortex beams integrated with the Metasurface are the nanoscale solution for the abovementioned issues. Previous studies have controlled the shape and size of the ideal vortex beam. This study demonstrates the broadband generation of polygonal perfect vortex beams through all-glass metasurfaces, aiming to manipulate the beam's shape while preserving its Orbital Angular Momentum (OAM) and radius. The presented metasurfaces carry an array of nanoantennas made of zinc sulfide material to generate a broadband perfect vortex beam within the visible spectrum, from 475 nm to 650 nm. For proof of concept, we have generated OV beams exhibiting multiple shapes like hexagons and octagons, and these shapes helped us make asymmetric intensity profiles. These irregular intensity distributions will help to create flexible optical traps for nanoparticles. The implications of our study include nano-optical trapping, optical manipulation, and optical communication.

Dispersion management plays a critical role in advancing spectrometers, which are indispensable tools for comprehending various optical phenomena, such as Raman scattering and fluorescence. Spectrometers investigate spectral changes under light-matter interaction, targeting many real-life applications extending from food safety and disease diagnostics to environmental monitoring. Unlike their bulkier predecessors, compact spectrometers have significant potential for enhanced versatility and wearable optics. This study proposes a zinc sulfide-based, all-dielectric super dispersive, Circular Polarization (CP) discriminator metalens. The dispersion-controlled metalens is an integral component of compact spectrometers, with focal spots residing on the same plane and undergoing minimal broadening across the visible spectrum (i.e., 475 − 650 nm). Moreover, the proposed device fulfills an additional role as a CP filter, permitting one state to focus on the intended position while simultaneously defocusing the other. In practice, incorporating a novel spin-decoupling approach with wavelength and phase multiplexing equips the proposed device to provide optimal spectral resolving performance with helicity-resolved capabilities, making it a multifunctional state-of-the-art meta-spectrometer. We are confident that the proposed device effectively merges various advanced features, positioning it as a promising addition to spectrometry.

Whispering Gallery Mode (WGM) microlasers were obtained by impregnating polystyrene microspheres in an aqueous solution of plasmonic nanoparticles and Rhodamine 6G. The emission spectra of Rhodamine-doped microspheres with diameters of 1 μm and 5-7 μm exhibited peaks corresponding to WGM, with a low Q-factor for 1-μm and a higher Q-factor for 5-7-μm spheres. The embedding of gold nanoparticles into microlasers results in a 40% decrease in the WGM intensity, while doping with silver nanoparticles increases it by 10%.

An anisotropic Ag@Au nanostructure is fabricated via physical vapor deposition of gold at oblique incidence onto a glass substrate with a preformed silver nanoparticle array. Utilization of silver nanoparticles as a scaffold for subsequent gold deposition makes it possible to control the size and shape of the gold capping layer. The obtained Ag@Au nanostructures are characterized by adjustable absorption bands and linear dichroism. The proposed technique provides for new opportunities in creation of plasmonic nanoparticles with targeted optical characteristics for applications in nanophotonics.