Temperature Dependence Of Refractive Index Research Articles

Temperature-dependent optical and dielectric properties of polyvinyl chloride and polystyrene blends in terahertz regime

Terahertz time-domain spectroscopy (THz-TDS) has been used to study the temperature-dependent refractive index, absorption coefficient and dielectric constant of polyvinyl chloride/polystyrene (PVC/PS) blends in frequency range of 0.2–1.8 THz. Moreover, the Sellmeier and thermo optic coefficients of PVC/PS blends with different weight ratios have been explored in the temperature range of 25–80 °C. These parameters are used to evaluate the dispersion properties of these blends in the observed frequency range. A clear indication of temperature dependence on the values of refractive index and the real dielectric constant of these blends have been observed. Their values decrease linearly with increasing temperature up to 80 °C. Whereas, no noticeable change has been observed in the imaginary dielectric constant and the absorption coefficient. These results provide a database of temperature-dependent optical and dielectric parameters of PVC/PS polymer blends for their efficient utilization for device fabrication in THz technology.

Characterization of SiNx grown at different nitrogen flow and prediction of refractive index using artificial neural networks

SiNx films were grown on silicon substrates by Radio Frequency (RF) magnetron sputtering deposition. The effect of nitrogen flow on the structural and optical properties of the obtained films was investigated using X-ray diffraction, Scanning Electron Microscopy (SEM), UV–Vis–NIR spectrophotometer and spectroscopic ellipsometer, respectively. XRD spectra of the films showed that all films belong to amorphous structure. SEM photographs of SiNx films were analyzed. As a result of the analysis, it was observed that the surfaces of the films had a homogeneous and smooth structure as the nitrogen flow increased. The total and diffuse reflectance spectra of the films were measured and the energy band gaps of the films were determined using the Kubelka-Munk function by using the diffuse reflectance. It was observed that the energy band gap changed as the nitrogen percentage increased. The refractive index of all films was obtained as a function of temperature using a spectroscopic ellipsometer. In the second part of this study, we focused on predicting the temperature dependent refractive indices of the nitrogen flow-dependent films using Artificial Neural Networks (ANN). For the training of the ANN model, wavelength and temperature values from experimental data were used as input and refractive index as output parameters. The simulation and prediction results obtained from this model are compared with the experimental data and interpreted. It is concluded that the ANN approach is suitable for simulating and predicting the temperature dependent refractive index. The models successfully trained with ANN will be especially preferred for predicting the refractive indices of SiNx films, which cannot be measured experimentally, thus providing predictions in non-experimental ranges. In particular, the results obtained by focusing on the ability of the developed artificial neural network (ANN) models to predict the optical properties of SiNx films and their potential to provide information in non-experimental conditions, offer a new approach to quickly and effectively evaluate the optical properties of SiNx films. This approach reveals the importance of artificial intelligence-based methods in materials characterization studies.

High sensitivity metamaterial thin film: bio and thermal sensors based on Fano resonances and nematic liquid crystals

ABSTRACT In this research, a new sensor was designed that exhibits high biological and thermal sensitivities. It is suitable for use as a biosensor, a thermal sensor, or both simultaneously. This nanostructure sensor is based on two non-identical copper rings, which are dependent on two dielectric environments, and has been optimised to enhance sensitivity. To control and increase the sensitivity of the designed metamaterial, the E7 liquid crystal was used, which has a temperature-dependent refractive index. The optimised data indicate that the highest sensitivity for the structural parameters; R, dr and d are 70, 43 and 30 nm, respectively. This nanostructure demonstrates a refractive index sensitivity of 500 nm/RIU and a very high temperature sensitivity of 11 nm/K in the wavelength range of 500–1000 nanometres and a temperature range of 290–330 Kelvin. The second peak has the highest sensitivity to the refractive index and the third peak has the highest sensitivity to temperature. The high temperature sensitivity reported is at a 90-degree orientation angle of the liquid crystal director. Therefore, the simulation and optimisation of this ultra-thin film indicates that it can be suitable for use as a high-quality bio-thermal sensor with a high figure of merit.

Measurement of the effective refractive index of silicon-on-insulator waveguide using Mach–Zehnder interferometers

We propose and demonstrate an accurate method of measuring the effective refractive index of silicon-on-insulator waveguides. By conducting the combined analysis to the troughs’ wavelength in spectra of Mach–Zehnder interferometers on chip. The wavelength-dependent and temperature-dependent effective refractive index of the fabricated waveguides are measured experimentally, and obtained the thermo-optic coefficient of silicon-on-insulator waveguides is about 2×10−4 /℃ in the 1550 nm communication band. The maximum measurement error for effective and group refractive index respectively are 1.5×10−5 and 1.5×10−3 obtained by numerical simulation. And an improved method for taking value of the free spectral range was discussed to obtain a more accurate group refractive index. It proves a fast and lost-cost measurement way to evaluate key optical parameters of waveguide, which can indicate the quality of fabrication process and optimize photonic components.

Temperature-dependent optical functions of selected Ge-Sb-Se bulk chalcogenide glasses obtained by spectroscopic ellipsometry

In this paper, we present spectroscopic ellipsometry measurements of five selected bulk chalcogenide glasses (Ge28Sb6Se66, Ge19Sb17Se64, Ge12Sb25Se63, Ge28Sb12Se60 and As40Se60) for broad wavelength range (0.3–15 μm) at the temperatures from room temperature up to glass transition temperature (with reserve). Temperature dependence of bandgap energy obtained from Tauc-Lorentz oscillator together with temperature dependence of refractive index for selected wavelengths (1.55, 3.4, 7.0 and 10.6 μm) where the studied materials are transparent are presented together with thermo-optic coefficients dEg/dT and dn/dT for these wavelengths.

Temperature dependence of refractive indices of InP , GaAs , AlAs , and In0.53Ga0.47As in the midinfrared spectral range determined by combined ellipsometry and Fourier-transform spectroscopy

We present the results of Fourier-transform measurements for determination of refractive indices of four semiconductor alloys in the midinfrared spectral range from 10 to 300 K. We investigate double-sided-polished, undoped InP and GaAs substrates as well as In0.53Ga0.47As/InP and AlAs/GaAs distributed Bragg reflector (DBR) mirrors with their operational wavelength designed for 4 µm. Through analysis of measured transmittance spectra supported by ellipsometry it is possible to determine the temperature-dependent refractive indices of InP and GaAs from 1.3 to 11 µm. Furthermore, by using reflectivity measurements supported by numerical modeling of the two types of designed DBR structures the refractive indices of In0.53Ga0.47As and AlAs for around 4 µm are determined with their temperature dependencies. Data acquired through this method could lead to improvement of already existing optical semiconductor devices expanding their application for longer wavelengths. Published by the American Physical Society 2024

Scattering by harmonically trapped 2D quantum gas near and around the critical regime

In this article, we analytically explore the quantum phenomena of scattering by harmonically trapped 2D quantum gases. We show the temperature’s dependence on the differential scattering cross-section (DSC) near and around the critical transition regime for both particle and light scattering cases separately. For the particle scattering case, we consider scatterers with quantized bound motion in a harmonic trap. Our findings on the structure factor for light scattering give phase transition phenomena for 2D bosonic atoms and the thermal behavior of the system. This result has practical significance for recent experimental setups such as in situ image analysis and bosonic simulations. Finally, we show the temperature-dependent refractive index for a 2D harmonically trapped bosonic medium. This parameter is important in neutron scattering experiments.

Temperature-dependent characterization of optical parameters in novel high birefringence nematic liquid crystal mixtures: an empirical investigation

This study investigates the temperature-dependent behaviors of three novel high-birefringence (Δn) nematic liquid crystals (NLCs) with varying clearing temperatures (T NI ). The high birefringence of the studied novel nematic liquid crystals is advantageous for LCD applications. It ensures fast response times, wide viewing angles, enhanced color reproduction, and reduced cross-talk, optimizing display performance and image quality. The goal is to characterize their order parameters (S(T)), effective geometry parameters (α eg), normalized polarizabilities, and crossover temperatures (T co ). Utilizing a modified four-parameter model for temperature-dependent refractive indices, we extract adjustable parameters and analyze their impact on T co and S(T). Three approaches, including the Vuks model, the Haller approximation model, and an effective geometry parameter-based model, are employed to assess S(T). The study focuses on four unknown parameters (A, B, (Δn) 0, and β) derived from the modified model, along with the nematic–isotropic transition temperature (T NI ). Findings reveal that a higher absolute value for the B parameter, a smaller β parameter value, elevated T NI values, and increased (Δn)0 values enhance the T co value.

Evolution and dynamics of spatial self-phase modulation in pyrromethene 567 for all-optical photonic diode applications

Spatial self-phase modulation has emerged as a novel and ubiquitous nonlinear optical effect, revealing potential application in all-optical devices for signal processing. The work investigates the evolution and dynamics of SSPM patterns in pyrromethene 567 (PM 567). A temperature-dependent refractive index gradient which induces a phase shift in the incident beam is responsible for the formation of spatial self-phase modulation. The non-linear response of PM 567 in different solvents and concentrations is investigated and tabulated. The effect of wavefront curvature, path length, and mechanical chopper on the formation of the SSPM patterns was studied. To our knowledge, an optical-diode-based unidirectional generation of spatial self-phase modulation in dyes has been reported for the first time. Simply cascading PM 567 dissolved in DMSO and Methanol having distinct nonlinear optical responses, an all-optical diode for unidirectional light propagation based on spatial self-phase modulation in PM 567 was achieved. The work reveals the potential application of PM 567 for achieving spatial asymmetry in light propagation based on SSPM in photonic devices for all-optical signal processing.

On the thermal response of multiscale nanodomains formed in trans-anethol/ethanol/water surfactant-free microemulsion

HypothesisSurfactant-free microemulsion (SFME), an emerging phenomenology that occurs in the monophasic zone of a broad category of ternary mixtures ‘hydrophobe/hydrotrope/water’, has attracted extensive interests due to their unique physicochemical properties. The potential of this kind of ternary fluid for solubilization and drug delivery make them promising candidates in many industrial scenarios. ExperimentsHere the thermodynamic behavior of these multiscale nanodomains formed in the ternary trans-anethol/ethanol/water system over a wide range of temperatures is explored. The macroscopic physical properties of the ternary solutions are characterized, with revealing the temperature dependence of refractive index and dynamic viscosity. FindingsWith increasing temperature, the ternary system shows extended areas in the monophasic zone. We demonstrate that the phase behavior and the multiscale nanodomains formed in the monophasic zone can be precisely and reversibly tuned by altering the temperature. Increasing temperature can destroy the stability of the multiscale nanodomains in equilibrium, with an exponential decay in the scattering light intensity. Nevertheless, molecular-scale aggregates and mesoscopic droplets exhibit significantly different response behaviors to temperature stimuli. The temperature-sensitive nature of the ternary SFME system provides a crucial step forward exploring and industrializing its stability.

Simple model for the calculation of concentration and temperature dependent refractive index of different solutions

Simple analytical models for the calculation of concentration (c) and temperature (T) dependent refractive index i.e., n(c,T) values of the six solutions namely, three electrolyte (KCl, NaCl, and CaCl2), a polar (glucose), a non-polar (ethyl acetate), and a protein (bovine serum albumin) solutions have been proposed. The values of refractive index obtained using our proposed models have been compared with the corresponding values of the refractive index obtained using other reported models and the experimental values. A fairly good agreement between them has been obtained.

Temperature-dependent THz properties and emission of organic crystal BNA.

As high-average power ultrafast lasers become increasingly available for nonlinear conversion, the temperature dependence of the material properties of nonlinear crystals becomes increasingly relevant. Here, we present temperature-dependent THz complex refractive index measurements of the organic crystal BNA over a wide range of temperatures from 300 K down to 80 K for THz frequencies up to 4 THz for the first time. Our measurements show that whereas the temperature-dependent refractive index has only minor deviation from room temperature values, the temperature-dependent absorption coefficient decreases at low temperature (-24% from 300 K to 80 K). We additionally compare these measurements with conversion efficiency and spectra observed during THz generation experiments using the same crystal actively cooled in the same temperature range, using an ultrafast Yb-laser for excitation. Surprisingly, the damage threshold of the material does not improve significantly upon active cooling, pointing to a nonlinear absorption mechanism being responsible for damage. However, we observe a significant increase in THz yield (+23%) at lower temperatures, which is most likely due to the reduced THz absorption. These first findings will be useful for future designs of high-average power pumped organic-crystal based THz-TDS systems.

Temperature-dependent optical properties of monocrystalline CaF2, BaF2, and MgF2

CaF2, BaF2, and MgF2 are low-index, infrared-transparent materials that are extensively used in optical systems. Despite their technological importance, a systematic investigation into the temperature dependence of their optical properties is lacking. In this study, spectroscopic ellipsometry was used to obtain the refractive index of monocrystalline CaF2, BaF2, and MgF2 for wavelengths between 220 nm and 1700 nm, and for temperatures between 21 °C and 368 °C. The raw ellipsometric data was fit to a Sellmeier model with temperature-dependent oscillator terms to extract the real part of the refractive index of each material. The refractive index of CaF2 and BaF2 was observed to decrease linearly with increasing temperature, which can be largely attributed to a reduction in the mass density due to thermal expansion. In contrast, the refractive index of MgF2 was found to vary nonlinearly with temperature, which suggests competing effects from the material’s electronic polarizability. The temperature-dependent refractive index data reported here provide a finely-resolved mapping of the thermo-optic coefficient for these three materials, which could inform the development of optical devices operating at elevated or unsteady temperatures.

An Edge-Filtered Optical Fiber Interrogator for Thermoplastic Polymer Analysis.

The present paper deals with the determination of thermodynamic quantities of thermoplastic polymers by using an optical fiber interrogator. Typically, laboratory methods such as differential scanning calorimetry (DSC) or thermomechanical analysis (TMA) are a reliable state-of-the-art option for thermal polymer analysis. The related laboratory commodities for such methods are of high cost and are impractical for field applications. In this work, an edge-filter-based optical fiber interrogator, which was originally developed to detect the reflection spectrum of fiber Bragg grating sensors, is utilized for the detection of the boundary reflection intensities of the cleaved end of a standard telecommunication optical fiber (SMF28e). By means of the Fresnel equations, the temperature-dependent refractive index of thermoplastic polymer materials is measured. Demonstrated with the amorphous thermoplastic polymers polyetherimide (PEI) and polyethersulfone (PES), an alternative to DSC and TMA is presented as the glass transition temperatures and coefficients of thermal expansion are derived. A DSC alternative in the semi-crystalline polymer analysis with the absence of a crystal structure is shown as the melting temperature and cooling-rate-dependent crystallization temperatures of polyether ether ketone (PEEK) are detected. The proposed method shows that thermal thermoplastic analysis can be performed with a flexible, low-cost and multipurpose device.

Design of Temperature Sensor Based on One-Dimensional Photonic Crystal Containing Si–BGO Layer

This paper describes the theoretical investigation of enhancement in temperature sensitivity using one-dimensional (1D) symmetric defective photonic crystal (PC) containing Si (Silicon) and Bi4Ge3O[Formula: see text] (Bismuth Germanate, BGO) material. The proposed sensor consists of a defect layer (air defect) sandwiched between two 1D-PCs with a symmetrical and asymmetrical structure composed of Si and BGO, respectively. Sensor performance has been evaluated by calculating the transmittance spectra of the proposed structure. In order to obtain the transmittance spectra, a transfer matrix method (TMM) is employed. The principle of temperature sensing is based on the shift in the resonant wavelength (or peak) of the transmission mode with a change in temperature. This is due to the temperature-dependent refractive index of the Si and BGO layers. Analysis of the transmittance spectra shows that temperature sensitivity of 1D-PC structure can be enhanced by using a symmetric defective PC with and without an external defect layer over asymmetric defective PC. It is found that symmetric defective PC with and without defect shows sensitivity equal to 0.173[Formula: see text]nm/[Formula: see text]C and 0.140[Formula: see text]nm/[Formula: see text]C, whereas asymmetric defective PC shows 0.125[Formula: see text]nm/[Formula: see text]C, for the same parameters. Further, the results show that symmetric defective 1D-PC (without the presence of any external defect layer) gives a higher [Formula: see text]-factor than a symmetric and asymmetric defective 1D-PC with an external defect layer. The proposed structure is cost-effective, easy to fabricate and compact in size.

Refractive index and domain structure of undoped and Nb doped (Na0.41K0.09Bi0.50)TiO3 (NBT-KBT) single crystal grown at MPB composition

Single crystals of undoped and Nb doped NBT-KBT with morphotropic phase boundary composition [(Na0.41K0.09Bi0.50)TiO3] were grown by spontaneous nucleation technique. The lattice parameter was found to be unaffected on Nb doping. Further the temperature dependent refractive indices were measured for four different wavelengths and the Sellmeier coefficients were calculated in the range of 30–160 °C. Refractive index was found to increase linearly with temperature (thermal coefficient of refractive index ∼10−4-10−5/°C). Further, the thermal coefficient was found to increase with the Nb concentration. A set of relations of the thermal coefficient of refractive index as a function of wavelength was established. In addition, the crystal was investigated using polarized light optical microscope. Regions with both ‘a’ and ‘c’ domains, typical of tetragonal structure, were observed in the samples. Further, the conoscopic study revealed that the material is of negative uniaxial type. The presence of domains related to the tetragonal and rhombohedral structures hints the possible coexistence of both the structures as expected for the morphotropic phase boundary composition. The outcome of the investigation would provide valuable inputs about NBT-KBT single crystals for photonic or optoelectronic applications.

Temperature controllable Goos–Hänchen shift and high reflectance of monolayer graphene induced by BK7 glass grating

BK7 glass has an unusual temperature-dependent refractive index and thickness, which provides a promising platform for uncovering the temperature-related optical phenomena and applications. Here, we theoretically demonstrate that monolayer graphene based BK7 glass grating structure has two Goos–Hänchen (GH) peaks with respective magnitudes of and and their corresponding reflectances are also high. The electromagnetic field distribution in this structure directly reveals that the enhanced GH shifts can be ascribed to the excitation of the guide mode resonances in the waveguide dielectric layer below BK7 glass grating structure and their high reflectances are granted by the constructive interferences between the reflected waves. In addition, the magnitudes of the GH peaks can be controlled by the temperature of BK7 glass as well as the chemical potential of monolayer graphene. We also evaluate the temperature sensing property of this structure based on the GH shifts and find that its maximum temperature sensitivity can be up to The enhanced and controlled GH shift presented in monolayer graphene based BK7 glass grating structure shows promise for the applications, such as, optical sensors, temperature sensors, and optoelectronic detectors.

Influence of phonon harmonicity on spectrally pure resonant Stokes fields

Due to their highly coherent emission, tunability, and compactness, integrated single-frequency diamond Raman lasers are interesting tools for applications in integrated quantum technology, high-resolution spectroscopy, or coherent optical communications. While the fundamental emission linewidth of these lasers can be Fourier limited, their thermo-optic characteristics lead to drifts in their carrier frequency, posing important challenges for applications requiring ultrastable emission. We propose here a method for measuring accurately the temperature-dependent index of refraction of diamond by employing standing Stokes waves produced in a monolithic Fabry-P\'erot diamond Raman resonator. Our approach takes into account the influence of temperature on the first-order phonon line and the average lattice phonon frequency under intense stimulated Raman scattering conditions. We further utilize this model to calculate the value of the average phonon frequency and then the temperature-dependent thermo-optic coefficient. The theory is accompanied by the demonstration of tunable Fourier-limited Stokes nanosecond pulses with a stabilized center frequency deviation of less than $4$ MHz.

Thermal, optical, and volumetric studies on mixing properties of binary nematic mixtures of 9CHBT/11CHBT

• Phase diagrams of a series of binary nematic mixtures (9CHBT/11CHBT) were studied by DSC method. • The modified four-parameter model was used by fitting the experimental data. • The temperature dependence of refractive indices, birefringence and order parameters in nematic phase was investigated. • Quantum chemical calculations on the nematogens provide supportive picture of the optical measurements. Phase diagrams and optical properties of a series of nematic binary mixtures composed of 4-(trans-4′-n-nonylcyclohexyl) isothiocyanatobenzen (9CHBT) and 4-(trans-4′-n-undecylcyclohexyl) isothiocyanatobenzen (11CHBT) were established in the entire range of molar fraction by differential scanning calorimetry method, refractometry as well as density measurements. In this research the thermodynamic, optical, and volumetric properties of the eutectic mixture ( E 9 , 11 ) composed of 9CHBT and 11CHBT ( x 11 C H B T = 0.4 ) were studied and interpreted. The binary phase diagram is in comparable with that predicted from Schroder–van Laar equation. The excess functions were determined using the calculated activity coefficients of the eutectic mixture. Moreover, the temperature dependence of refractive indices, birefringence, and order parameters of the pure nematogens and the binary eutectic mixture was investigated. In contrast to the individual nematogens, the eutectic mixture ( E 9 , 11 ) displays a crossover temperature ( T CO ) based on the four-parameter model. Finally, results from quantum chemical calculations on the studied nematogens provide an overall supportive and coherent picture of the thermal, optical measurements. All calculations were performed using the Turbomole software package. The used methodology allows for an acceptable approximation of effective polarizabilities.

Temperature dependence of refractive indices of Al0.9Ga0.1As and In0.53Al0.1Ga0.37As in the telecommunication spectral range

In this work, we determine the temperature dependence of refractive indices of In0.53Al0.1Ga0.37As and Al0.9Ga0.1As semiconductor alloys at telecommunication wavelengths in the range from room temperature down to 10 K. For that, we measure the temperature-dependent reflectance of two structures: with an Al0.9Ga0.1As/GaAs distributed Bragg reflector (DBR) designed for 1.3 µm and with an In0.53Al0.1Ga0.37As/InP DBR designed for 1.55 µm. The obtained experimental results are compared to DBR reflectivity spectra calculated within the transfer matrix method to determine refractive index values. We further show that changes due to the thermal expansion of the DBR layers are negligible for our method.