Refractive Index Research Articles

Linear and Nonlinear Optical Properties of Symmetric and Asymmetric Double Triangular Quantum Dots Withinside the Presence of Magnetic Field

AbstractLinear and third‐order nonlinear optical absorption coefficients and relative refractive index changes in symmetric and asymmetric double triangular quantum dots are examined theoretically. The dependence of these optical properties on the magnetic field is examined. After calculating energies and wave functions within the effective mass and parabolic band approaches, analytical expressions of linear and nonlinear optical properties are obtained using the compact density matrix approach and iterative method. Numerical calculations are presented for typical GaAs/AlGaAs material. The results show that the magnetic field causes different effects on the and transitions. Moreover, the calculated results also reveal that the resonance frequency and nonlinear contribution are different in symmetric and asymmetric structures. As a result, it is concluded that the magnetic field plays a vital and important role in the electronic and optical properties of the system and can be used to tune the inter‐subband transitions and change the corresponding optical sensitivities.

All-dielectric ellipsoidal tetramer metasurface sensor with multi-resonances from the bound states in the continuum.

We demonstrate an all-dielectric tetramer metasurface that achieves high-precision refractive index sensing through the excitation of toroidal dipole, magnetic dipole, and electric quadrupole modes, driven by bound states in the continuum (BIC). The metasurface exhibits exceptional performance, with a quality factor of 4.65 × 104, a sensitivity parameter of 649 nm/RIU, and a figure of merit of 1.51 × 104 RIU-1, achieved by optimizing symmetry and lattice perturbations in periodic silicon tetramer ellipsoidal nanodisks on a SiO2 substrate. Additionally, the sensor effectively distinguishes analytes with extinction coefficient differences as small as 0.01 through enhanced broadband absorption. This innovation demonstrates substantial potential for label-free sensing applications in microfluidic chip integration.

Combining Infrared Refraction and Attenuated Total Reflection Spectroscopy.

We have specified and obtained a ZnSe prism with an unconventional face angle cut to 30°. This prism, with internal incidence angles ranging from 30° to 48°, allows users to record internal reflection spectra below the critical angle and attenuated total reflection (ATR) spectra above the critical angle without the need to change optics or move or replace the sample. We demonstrate its capabilities using 102 spectra of benzyl benzoate taken with s- and p-polarization at different angles of incidence. The subcritical spectra were analyzed to obtain n∞, a key parameter for correcting the ATR spectra. These corrected spectra were subsequently used to determine the complex refractive index for all ATR measurements. The averaged complex refractive index function shows excellent agreement with that obtained through ATR spectroscopic ellipsometry.

Pulse length effects in the nonresonant long-wave infrared nonlinear optical response of n-Ge, GaAs, and ZnSe

Nonlinear optical refraction and nonlinear absorption are characterized in important long-wave infrared optical materials with picosecond and femtosecond laser pulses. The effective nonlinear refractive indices are found to be constant across a range of pulse parameters. Nonlinear absorption far from resonance is observed at relatively low (∼1GW/cm2) intensities in these materials, and the onset intensity and fluence scale strongly with pulse length. A free carrier dominated nonlinear absorption mechanism is identified for picosecond pulses, whereas nonperturbative photoionization causes femtosecond absorption.

Robust Light Detection from Ultraviolet to Near‐Infrared with ZnGa2O4/p‐Si Heterojunction Photodiode and Its Application for Optoelectronic Physically Unclonable Functions

AbstractThe Si‐based self‐powered broadband photodiode (SSBP) is prized for its ability to swiftly detect light across a wide spectrum without requiring an external voltage. However, boosting its efficiency remains challenging due to its high refractive index and limited UV light penetration. A combination of Si with ZnGa2O4, an ultra‐wide‐bandgap spinel material, can bring new opportunities to address these shortcomings of SSBP. In this study, a ZnGa2O4/p‐Si heterojunction photodiode is presented, which is capable of detecting UV to near‐infrared light autonomously. Operating without bias, this device exhibits excellent rectification and detects wavelengths from 265 to 1000 nm, achieving impressive performance metrics such as a photo‐to‐dark current ratio of 5.8 × 104, response speed of less than 3 ms, responsivity of 117 mA W−1, and specific detectivity of 5.5 × 1012 Jones while the photodiode demonstrates exceptional stability and durability under harsh conditions. The versatility of this device is demonstrated by applying it to the optical imaging sensors and physically unclonable security devices. This study provides new inspirations for the development of the energy‐efficient and emerging optical sensing technologies.

High-Q fano resonance metasurface sensor for refractive index and methane gas concentration measurement

High-quality-factor Fano resonances excited by metasurfaces have been playing an important role in the field of optical sensing. A high-performance sensor for refractive index and methane concentration measurement is designed and prepared in this paper. The symmetry of the structure is broken by altering the size of the rectangular holes in the tetramer, resulting fano resonance Q-factor of 34176 and modulation depth of 100%. The finite-difference time-domain (FDTD) method is used to simulate the structure. The results show that the refractive index and methane concentration sensitivity are 325 nm/RIU and −1.44 nm/%, respectively. The FOM can achieve 10156 RIU−1. Furthermore, experiments are carried out on the gas application of the structure and the sensitivity of methane concentration is −1.03 nm/%. Therefore, the proposed metasurface has more practical and feasible significance in background refractive index and gas environment monitoring.

Multi-Particle sorting using signals from particles trapped by single optical fiber tweezers

We propose a multi-particle sorting method based on single optical fiber tweezer particle-trapped signals. When particles are trapped to the optical axis, the instantaneous trapped signal is collected by the photodetector. There are significant differences in the instantaneous trapped signal intensity for particles with different refractive indices. Specifically, the variation in instantaneous trapped signal intensity correlates well with changes in the refractive index of the particles in a linear relationship. We conducted 60 sets of experiments, which showed that the method accurately sorts yeast cells, silica (SiO2) microspheres, and polystyrene (PS) microspheres. Additionally, the method’s simple structure, high accuracy, ability to simultaneously sort multiple particles, and potential to handle large quantities of particles provide a new approach to particle identification and detection. Consequently, this method is widely used in chemistry, microbiology, and medical diagnostics.

Light scattering by Möbius particles

Using the Discrete-Dipole Approximation (DDA) we study scattering-angle dependences of the orientationally averaged Mueller matrix elements for small Möbius particles with different chirality. A Möbius particle is a strip of a certain width and thickness, the ends of which are attached to each other after twisting one of them at an angle by a multiple of □. The Mueller matrices Mik for such particles have 16 non-zero elements. The scattering-angle dependences of the intensity M11, linear polarization degree (-M12/M11), and Circular Intensity Differential Scattering (CIDS = -M14/M11) show their sensitivity to the refractive index and number of the strip twisting. For instance, the CIDS depends significantly on the complex part of the refractive index. Particles with more twists show a decrease in the maximum value of the positive branch of linear polarization and an increase in the width and minimum of the negative branch. The twist parameter's influence on CIDS is non-monotonic, initially increasing and then approaching zero with further twisting.

Recent Developments and Prospects of Electromagnetically Active Metamaterials in Biosensing

This paper provides an overview of the progress of research on electromagnetically active metamaterials in the field of biosensing, especially the potential of terahertz metamaterials for biosensor applications. Electromagnetically active metamaterials exhibit a negative refractive index and perfect absorption through their special structure, and their electromagnetic behavior is affected by their structure and geometry, which is different from traditional materials. The article reviews the application of terahertz technology for the bio-detection of cancer cells and apoptotic processes using periodic metal arrays by terahertz biosensors, demonstrating the advantages of terahertz biosensors, such as high sensitivity and detection without labeling. This paper presents a comprehensive overview of the advancements in research concerning electromagnetically active metamaterials within the domain of biosensing, with a particular emphasis on the potential applications of terahertz metamaterials in biosensor technology. Electromagnetically active metamaterials are characterized by their negative refractive index and perfect absorption, which arise from their distinctive structural properties. The electromagnetic behavior of these materials is significantly influenced by their design and geometry, setting them apart from conventional materials. The article examines the utilization of terahertz technology for the bio-detection of cancer cells and apoptotic processes tunability, employing periodic metal arrays in terahertz biosensors. It underscores the advantages of terahertz biosensors, which include high sensitivity and the capability to detect biological entities without the necessity for labeling. Terahertz metamaterial biosensors are promising for protein, virus, and cancer cell detection. This paper also explores the design and application of chiral metamaterials, especially indium tin oxide-based mid-infrared chiral metamaterials, to solve the problem of the large size of traditional materials and investigates their circular dichroism. Looking ahead, electromagnetically active metamaterials, especially terahertz metamaterials, are expected to improve resolving power and sensitivity, reduce costs, and expand the applications of biosensors in the biomedical field. The applications and research of these sensors will continue to advance with the advancement of micro and nanoprocessing technologies.

Titanium oxide hydrates as versatile polymer crosslinkers and molecular‐hybrid formers

AbstractMolecular hybrid materials based on widely available polymers crosslinked with an inorganic species have received increasing interest for their unique property sets outside of the usual range of commodity plastics and/or nanocomposites. Here, we provide a mini‐review on molecular hybrids based on metal oxide hydrates—compounds that readily react with, for example, hydroxylated polymers to form inorganic:organic materials systems with many desirable features and properties. Focusing on titanium oxide hydrates, we discuss here that such molecular hybrids can exhibit a broad refractive index range in addition to an increased glass transition temperature, mechanical stiffness and swelling resistance in comparison to the neat polymer, which illustrates that such hybrid systems offer a new, low‐cost, robust and versatile functional materials platform with great promise for, for example, solution‐processed photonics, catalysts and antimicrobial coatings. Generally, our mini‐review seeks to provide a concise and accessible overview of titanium oxide hydrate:polymer hybrid systems, focusing on their unique properties and processability as well as their broad and largely untapped potential as functional materials. © 2024 The Author(s). Polymer International published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Flexible and innovative PVA/ZrO2/g-C3N4/CNT nanocomposites film for optoelectronic applications

This study successfully prepared polyvinyl alcohol (PVA) polymer films doped with ZrO2/(g-C3N4/CNT) nanofillers using the solution casting technique. The crystal structure of the nanocomposite films was characterized by X-ray diffraction (XRD), revealing the semi-crystalline nature of PVA and an average ZrO2 crystallite size of 13.17 nm. Fourier-transform infrared (FTIR) spectroscopy confirmed the chemical composition and functional groups present in the nanocomposites. Scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) analysis showed uniform dispersion of the nanofillers without noticeable phase separation, with EDX confirming the successful incorporation of ZrO2, g-C3N4, and CNT into the PVA matrix. X-ray photoelectron spectroscopy (XPS) further validated the elemental composition and chemical states, indicating the presence of carbon, oxygen, nitrogen, and zirconium. Optical analysis demonstrated that increasing ZrO2/(g-C3N4/CNT) content reduced the direct and indirect band gaps from 5.41 eV to 5.25 eV and from 5.18 eV to 4.92 eV, respectively. In addition, the single-oscillator energy (E0) and dispersion energy (Ed) increased, while the static refractive index (n0) decreased. Improvements were also observed in linear optical susceptibility (χ(1)) and third-order nonlinear optical susceptibility (χ(3)), enhancing the polarizability of the polymer molecules. These results indicate that PVA films doped with ZrO2/(g-C3N4/CNT) hold promise for optoelectronic applications due to their enhanced optical properties.

Displaced thinned single-mode fiber Mach-Zehnder interferometer tested for temperature and curvature applications

This article explains the features and qualities of employing a thinned manufacturing fiber to assemble a Mach-Zehnder interferometer (MZI) for detecting two physical variables: temperature and curvature. The MZI comprises a filter by splicing core-offset sections of a thinned fiber (TF) cladding diameter of 80 μm in an SMF-TF-SMF configuration. The TF splices act as the arms of the MZI, while the mismatch diameter sections serve as optical fiber couplers. The optical spectrum analyzer (OSA) detects the transmitted light and analyzes its optical transmission characteristics, showing 11 peaks of modal interferences into the longitude region. As a result of the experimental arrangement, the curvature and temperature sensitivities are 0.49 nm/m−1, 0.01 nm/°C, and 0.09 nm/°C for temperatures of 0–60 °C and 70–130 °C, respectively. The proposed sensor has potential advantages for measuring refractive index, pH, torsion, curvature, and temperature.

LArRI — A new setup for Liquid Argon Refractive index measurement

Liquid argon (LAr), widely used as the active target in neutrino and dark matter experiments, is a scintillator with a light yield of approximately 40 photons/keV. The scintillation spectrum is centered at 128 nm, and the attenuation length is of the order of meters, depending on the purity. The addition of small amounts of dopants allows for shifting the scintillation peak simplifying the light detection and opening the possibility to the development of imaging systems. There is no precise knowledge of the optical properties of LAr in the VUV range, but it could be exploited to improve the performances of liquid argon-based experiments, especially when the involved mass is in the ton scale. LArRI (Liquid Argon Refractive Index) aims to directly measure the refractive index of LAr in the VUV spectrum, using an interferometric technique. The refractive index is obtained by comparing two interference patterns, created in vacuum and liquid, acquired with cryogenic silicon photomultipliers. This work primarily presents the methodology, the preliminary tests, and the analysis strategy, which are intended to be applied to real data shortly.

Exploring the optical properties of naphdiyne sheet: First-principles study

Naphdiyne sheet is a two-dimensional carbon-based structure composed of naphthyl rings and acetylenic linkages. The optical characteristics of naphdiyne sheets are investigated using density functional theory. The results showed that this sheet is suitable for energy storage systems due to its high dielectric constant. The dielectric constant of naphdiyne is higher than that of graphene. The refractive index, absorption, reflection, and transmission coefficients are calculated based on the dielectric function. A notable optical absorption is observed across a wide energy range for parallel polarization. The transparency of this material is evident in its reflection and transmission constants, particularly in high-energy regions. The findings suggest that the naphdiyne sheets hold promise for use in nanoelectronics and optoelectronics.

Investigating the structural, electronic, optical and thermodynamic properties of ATiO3 (A = Ba, Ca, Ra) for low-cost energy applications

The structural, optoelectronic, and thermodynamic characteristics of ATiO3 (A = Ba, Ca, Ra) perovskites have comprehensively been investigation first-principles based DFT calculations. The GGA method was employed to handle exchange and correlation potentials. The analysis of the E-V plots indicates that RaTiO3 exhibits the highest level of stability in comparison to BaTiO3 and CaTiO3. The direct band-gap characteristic of the ATiO3 (A = Ba, Ca, Ra) perovskites is apparent in the band structure plots. The band gaps for BaTiO3, CaTiO3, and RaTiO3 are 2.48, 3.15, and 1.91 eV, respectively. The analyzed materials exhibit the highest level of photon absorption in the near UV area, as demonstrated in the ε2(ω) plots. The refractive index n(ω) values reveal that ATiO3 (A = Ba, Ca, Ra) are active optical materials as their n(ω) values are between 1 and 2. These perovskite oxides have optical features that make them promising prospects for anti-reflecting coatings over entire energy span as these materials exhibits a very low reflection (∼20 %) of incident photons. The thermodynamic properties of ATiO3 (A = Ba, Ca, Ra) are assessed to determine their dynamical stability and suitability for thermal applications. The results of the investigation demonstrate that these perovskite oxides have the potential to be used in optoelectronic devices.

Small compressive strain tuning of α-TeO2 and β-TeO2 polymorphs: Electronic, linear, and nonlinear optical properties from first-principles calculations

This study examines the effects of 2 % compressive strain on the structural, electronic, and optical properties of α-TeO2 and β-TeO2 polymorphs. α-TeO2’s bandgap increases from 3.64 eV to 3.70 eV, while β-TeO2’s decreases from 3.632 to 3.53 eV. Lattice parameters uniformly reduce in α-TeO2, but vary dissimilarly in β-TeO2. PDOS analysis shows O-2p and Te-5p states dominate near the band edges. Optical behavior is anisotropic, with enhanced polarizability and refractive indices under strain. Nonlinear optical properties improve with increased strain, especially the non-linear susceptibility components, which are relevant for second-harmonic generation. Born Effective Charges show increased Te polarization and reduced oxygen polarization, impacting dielectric response.

Optimised structural, electronic, optical and mechanical properties of SrTiO3-xHx for photovoltaic applications: a DFT insight

Density Functional Theory (DFT) computations, by CASTEP code with GGA-PBE correlation functional, for SrTiO3-xHx have been carried out to compute elastic, mechanical, structural, electronic, and optical characteristics of SrTiO3-xHx perovskite hydride material at varied levels of replacements (x = 0, 0.3, 0.6, 0.9, 1.2, 1.5, 1.8, 2.1, 2.4, 2.7, and 3.0). With the doping of hydrogen, the structure changed from cubic to orthorhombic and then tetragonal. Elastic parameters and negative value of formation energies demonstrate the durability and formability of these materials. It is established that these compounds are brittle by examining the B/G ratio and Poisson ratio. A bandgap is increased from 1.791 eV to 2.441 eV as dopant concentration rises, changing the semiconductor's nature from indirect to direct. Additionally, a detailed explanation of the optical properties for photons in the energy spectrum of 0–10 eV was provided dielectric functions, refractive indices, extinction coefficients, and 0–50 eV were provided including reflectance, absorbance, and energy loss. By increasing hydrogen doping, the highest absorption peak in the visible region is observed for x = 2.1, which shows that SrTiO3-xHx perovskite hydride has revealed stronger potential for photovoltaic applications.

Analysis and Optimization of Light Absorption and Scattering Properties of Metal Nanocages.

Metal nanocages exhibit localized surface plasmon resonance that strongly absorbs and scatters light at specific wavelengths, making them potentially valuable for photothermal therapy and biological imaging applications. However, investigations on metal nanocages are still confined to high-cost and small-scale synthesis. The comprehensive analysis of optical properties and optimal size parameters of metal nanocages is rarely reported. This paper simulates the effects of materials (Ag, Au, and Cu), size parameters, refractive index of the surrounding medium, and orientation on the light absorption and scattering characteristics of the nanocages using the finite-element method and the size-dependent refractive-index model for metal nanoparticles. The results show that the Ag nanocages have excellent light absorption and scattering characteristics and respond significantly to the size parameters, while the refractive index and orientation of the surrounding medium have less effect on them. The Au nanocages also possess superior light absorption properties at specific incident wavelengths. This study also identified the optimized sizes of three metal nanocages at incident light wavelengths commonly used in biomedicine; it was also found that, under deep therapy conditions, Ag nanocages in particular exhibit the highest volume absorption and scattering coefficients of 0.708 nm-1 and 0.583 nm-1, respectively. These findings offer theoretical insights into preparing target nanocage particles for applications in photothermal therapy and biological imaging.

Optical interferometry based acoustic field characterization using physics informed neural networks

The acousto-optic effect offers a non-contact way of measuring and visualizing acoustic fields in transparent fluids. Acoustic density fluctuations induce changes in the media's refractive index that can be measured using interferometry. While sensing methods based on acousto-optics have gathered increasing attention, many of such methods are only sensitive to projections of the acoustic field along the optical path, limiting the fields that can be characterized to one or two dimensions, or requiring complex experimental setups. Recently, reconstruction methods that abide by the physics of acoustic wave propagation showed unparalleled performance compared with classical reconstruction methods, reducing the sampling requirements and enabling to characterize three-dimensional acoustic fields. Nonetheless, such reconstruction methods rely on discrete approximations which might be poor at describing spatially complex fields. In this work we use physics-informed neural networks (PINNs) to estimate the acoustic pressure over space from interferometer measurements. The network is flexible enough to represent complex acoustic fields, while its output is constrained to fulfill the wave equation. Once trained on the data available for a given experiment, the PINN can estimate the acoustic pressure at arbitrary positions. The approach is tested in an experimental study, showing an improved performance compared with state-of-the-art reconstruction methods.

Double-layer optical fiber interferometer with bio-layer-modified reflector for label-free biosensing of inflammatory proteins

This work discusses label-free biosensing application of a double-layer optical fiber interferometer where the second layer tailors the reflection conditions at the external plain and supports changes in reflected optical spectrum when a bio-layer binds to it. The double-layer nanostructure consists of precisely tailored thin films, i.e., titanium (TiO2) and hafnium oxides (HfO2) deposited on single-mode fiber end-face by magnetron sputtering. It has been shown numerically and experimentally that the approach besides well spectrally defined interference pattern distinguishes refractive index (RI) changes taking place in a volume and on the sensor surface. These are of interest when label-free biosensing applications are considered. The case of myeloperoxidase (MPO) detection—a protein, which concentration rises during inflammation—is reported as an example of application. The response of the sensor to MPO in a concentration range of 1 × 10−11–5 × 10−6 g/mL was tested. An increase in the MPO concentration was followed by a redshift of the interference pattern and a decrease in reflected power. The negative control performed using ferritin proved specificity of the sensor. The results reported in this work indicate capability of the approach for diagnostic label-free biosensing, possibly also at in vivo conditions.