Spectroscopic investigation of polyimide-based long-range surface plasmon resonance for mineral oil hydrocarbon detection in edible oils.

Research on the rapid measurement of the three-dimensional refractive index profile of active optical fiber preforms based on regional reconstruction from a small number of holograms

Disentangling the events that constitute the main phase transition of predominantly neutral lipid bilayers containing anionic lipids by measuring their macroscopic properties.

Thermally triggered solvent-responsive "afterglow" structural coloration system based on double-inverse opal photonic crystals.

High-precision refractive index measurement system and method for solutions based on insertion-type spectral interferometry

Smartphone-integrated LSPR-based U-shaped optical fiber sensor for refractive index and salinity sensing

Peptide diagnostics serve an important role for initial disease recognition, pharmaceutical evaluation, and environmental monitoring. Conventional methods for diagnosis typically involve labelling concepts that reduce sensitivity, increase test complexities, and limitations in real-time analysis. In the proposed work, we have introduced Corner-Triangle, Floral Geometry Refractive Index Biosensor (CTFGRIB) for monitoring peptide concentrations by names, Glycylleucine (Gly-Leu), Triglycine (Tri), Glycine (Gly), Glycytyrosine (Gly-Tyr), Diglycine (Dig), and Glycylaspartate (Gly-Asp) with a combination of machine learning evaluation. A periodical arrangement of corner-triangle patterns surrounded by a floral layout, as a distinctive geometry, provides a number of synergistic benefits that directly boost biosensing capabilities. The parametric assessments involve outstanding performance parameters with the favourable values of sensitivity being 1023.25 nm/RIU, and favourable values of detection limit are 0.0733 RIU for the Gly-Leu peptide cell. The favourable quality factor value of 24.0368, and the figure of merit value of 10.9508 RIU-1 have been achieved for the Gly-Leu peptide cell. The favourable transmittance rate of 33.6%, 33.3%, 33.0%, 33.0%, 32.9%, and 32.9% have been observed for Gly-Leu, Tri, Gly, Gly Tyr, Dig, and Gly-Asp, respectively. The optimised R squared value of 0.997604 and the MSE value of 9.607930 × 10-05 have been achieved from the machine learning method.

High-sensitivity and high-specificity optical fiber SPR doxorubicin sensor enabled by Ti3C2 MXene sensitization.

Variable refractive index waveguides for mid-infrared sensing

Novel cubic Y4Zr3O12 transparent ceramics with high refractive index fabricated by pressureless sintering

Boron-irradiated Si3N4: the origin of the defect responsible for the red shift of fundamental absorption edge and increase of refractive index

Diffusive modeling and Monte Carlo analysis of random-laser-base optical sensors for dual refractive index and temperature detection

While quasi-bound states in the continuum (Q-BICs) enable vivid structural colors, their performance is often compromised by higher-order resonances at short wavelengths that limit spectral purity. This paper presents a dual-layer all-dielectric metasurface that overcomes this challenge through refractive index matching. The design not only suppresses short-wavelength resonances but also enhances the far-field coupling of the main resonance. It achieves continuous hue and brightness tuning across the visible spectrum, delivering colors with exceptional monochromaticity (<5 nm FWHM), high saturation (>90%), and a wide gamut covering 150.2% of sRGB. This study provides a robust solution for advanced display, data storage, and anti-counterfeiting applications.

Aerosol particles that contain brown carbon (BrC) chromophores will absorb solar radiation, with important implications for their effects in the environment. Although UV/vis spectroscopy of bulk BrC samples can be used to characterize absorption spectra, these methods can be of limited use when applied to aerosol particles due to high chromophore concentrations and the formation of metastable supersaturated or supercooled states in atmospheric particles. Here, we report a method to characterize the absorption spectra of levitated aqueous particles in a linear-quadrupole electrodynamic balance using broadband light scattering, allowing the wavelength dependence of the imaginary component of the refractive index, k, to be determined from a single spectrum. We show that a non-absorbing particle is an effective reference for the illuminating light and provides a reliable indication of the intensity variation across the measured wavelength range. This allows spectra from sample particles containing light-absorbing components to be referenced and normalized in a way that decouples the processed spectrum from any artifacts introduced by the LED spectrum and optical setup. Using this approach, we explore the pH-dependent absorption spectra of 4-nitrocatechol particles under a range of relative humidity (RH) conditions. We demonstrate sensitivity to k in the range 0.0001 to 0.01 and compare our results to predictions using bulk UV/vis data. This method allows the characterization of light absorption at much higher chromophore concentrations than traditional UV/vis measurements, enabling a more direct comparison to atmospheric aerosol particles.

Abstract New types of surface waves and the influence of optical parameters and temperature on their properties are analytically studied. Wave propagation along the surface of a photorefractive crystal with diffusion-type nonlinearity coated with a guiding layer with the refractive index gradient is considered. The refractive index is characterized by a monotonic decrease with a distance from the crystal surface into the depth of the guiding layer. Exact analytical solutions to the formulated equations describing two new types of surface waves with unique properties in the system under consideration are found. It is specified how the optical characteristics and temperature can influence on the properties of surface waves of both types based on the obtained solutions. It is enough to vary the temperature if it is necessary to change the wave properties only in a photorefractive crystal but in the layer so that they remain unchanged. In this case, for the oscillation frequency will change the waves of the first type and the depth of field penetration into the photorefractive crystal will change for both types of waves. It is necessary to the angle of incidence of the beam exciting the surface wave and the optical parameters of the refractive index profile of the gradient guiding layer to change the properties of the field distribution. The explicit expressions of power flows are obtained, using of which features of the spatial distribution of the energy density of surface waves between the crystal and the covering gradient guiding are established. The ways to control this distribution of surface wave energy density by varying optical parameters and temperature are identified.

Effect of Temperature, Alkyl Chain Length and Anions on the Density, Viscosity, Speed of Sound, Surface Tension and Refractive Index of [C2mim][MeSO4], [C2mim][EtSO4], [C2eim][EtSO4], [C3py][BF4], [C4py][BF4], [C4mpy][BF4] and [C6py][BF4] Ionic Liquids

Reflectance spectroscopy is notoriously confounding in that the spectral response is highly dependent upon morphology. Fortunately, all such perturbations are neatly encoded by the complex refractive index. Herein, we quantitatively model the infrared reflectance spectrum of a specularly flat pressed pellet sample of the birefringent compound, sodium nitrate. Single crystals of sodium nitrate were synthesized and spectroscopically analyzed using polarization-dependent single-angle reflectance spectroscopy. Once measured and validated, the optical constants were applied to model the pressed pellet reflectance spectrum. It was evident that an average of the anisotropic refractive indices was insufficient to account for the measured pellet reflectance. The Python package pyElli was used to calculate a basis set of orientation-dependent reflection spectra spanning the distinct φ and θ Euler rotations of the uniaxial crystal. When the population of orientations was allowed to vary freely in a spectral fit analysis, the fit-deduced orientations were tightly clustered along φ = 45°, hinting at residual anisotropy in the pressed pellet sample. Conversely, an equally valid spectral fit (with marginally worse fit metric) was obtained when the population was constrained to an isotropic distribution of orientations. Subsequent non-zero cross-polarization reflectance measurements likewise suggested anisotropy in the pellet. However, both grazing-incidence wide-angle x-ray scattering and scanning electron microscopy measurements revealed that the microcrystal orientations at the surface of the pressed pellet sample were isotropically distributed. Application of the measured complex refractive indices for modeling the reflectance spectrum of the pressed pellet, and rectification of these seemingly contradictory observations will be discussed.

Surface-enhanced Raman spectroscopy (SERS) offers high sensitivity for biomolecular detection, but its performance is often constrained by noise arising from signal non-uniformity across substrates. Here, we introduce a noise-management-oriented design strategy for hybrid SERS substrates composed of gold nanoparticles (AuNP) and two-dimensional (2D) materials (graphene, MoS2, and WSe2). Compared with conventional AuNP substrates, the hybrids exhibit markedly improved spectral uniformity and signal-to-noise ratio (SNR), with the AuNP/graphene platform reducing noise by ∼67% and increasing SNR by ∼279%. Full-wave simulations based on Maxwell's equations corroborated the experimental results and reveal that optical constants of the 2D material and nanoparticle distribution jointly govern noise characteristics. SNR dependence on nanoparticle density distributions, refractive index (n), and extinction coefficient (k) is further established. As a practical demonstration, the AuNP/graphene substrate enabled detection of the receptor binding domain protein at a limit of detection (LOD) of 10-9 M, representing a ten-fold improvement over the 10-8 M LOD of AuNP substrates. These results establish AuNP/2D hybrids as effective platforms for noise-managed SERS, offering enhanced sensitivity for biosensing.

Staining of tissue sections and subsequent microscopic imaging are two key steps in conducting conventional histopathological analysis, but these processes are complex and time-consuming, and the image analysis results largely depend on the experience of the operator. To overcome these limitations, this work proposes a label-free quantitative histopathological analysis method based on the hyperspectral surface plasmon resonance microscopy (HSPRM) system. The HSPRM system consists of a Kretschmann-type spectral SPR sensor and a hyperspectral microscope, which are optically connected through an imaging lens. The HSPRM system with an equilateral triangular prism coupler made of high-index glass can capture wavelength-scanning SPR images and pixel-resolved resonance wavelengths (RWs) of tissue sections, and allows for two-dimensional (2D) mapping of the refractive index (RI) of the tissue in a wide dynamic range by fitting the measured RWs pixel by pixel with the multilayer Fresnel model. As a result, the HSPRM system can easily distinguish the cancerous region from the normal region based on the measured 2D distribution of the RI of the tissue sample. This outstanding capability of the HSPRM system was verified through comparative tests of tumor tissue and normal tissue from mouse mammary glands. The experimental results indicated that the average RI of the tumor tissue is higher than that of the normal tissue. Multiple measurements demonstrated that the prerequisite for label-free quantitative histopathological analysis with the HSPRM system is to ensure gapless adhesion of the tissue section to the SPR sensor chip.

IONOLAB‑RAY is a modular ray‑tracing toolbox that models electromagnetic wave propagation through a realistic, time‑varying ionosphere represented by a three‑dimensional voxel‑based grid. Within each voxel, refractive indices are computed from the full Appleton‑Hartree formulation, accounting for anisotropy, magnetic field effects, and collisions. The physical parameters of the ionosphere are derived from background ionospheric model, which can be assimilated with Total Electron Content (TEC) data, allowing for the near real‑time updating of the statistical model to reflect current ionospheric conditions. The system simulates both ordinary and extraordinary propagation modes under varying geophysical conditions. Designed for global and near real‑time operation, IONOLAB‑RAY can be executed for any position on Earth and for varying ionospheric states. Its user‑friendly interface supports multiple‑run simulations, allowing users to analyze wave propagation under different scenarios and explore the influence of input parameters such as signal frequency, elevation, and azimuth angle. For each computed ray path, the toolbox determines key physical parameters – attenuation, phase and group velocity, and total propagation delay – and generates both virtual and real‑height ionograms. Real‑height ionograms, derived from actual ray trajectories, provide essential insights into true reflection altitudes and ionospheric structure. Through its flexibility, physical accuracy, and operational efficiency, IONOLAB‑RAY serves as a powerful framework for ionospheric modeling, propagation analysis, and space environment studies.