Dependence Of Refractive Index Research Articles

Temperature dependence of LiTaO3 refractive index: corrections of Sellmeier equation

We report a new and more precise Sellmeier equation obtained by using the analysis of quasi-phase-matching curves of the optical parametric generation (OPG) in 1D periodically poled LiTaO3 (1D-PPLT) of different grating periods.

Layer Dependence of Complex Refractive Index in CrSBr.

CrSBr is a recently discovered two-dimensional anti-ferromagnet. It has attracted much attention due to its superior properties for potential optoelectronic and spintronic applications. However, its complex refractive index with layer dependence has not been systematically studied yet. In this work, we studied the room-temperature complex refractive indices of thin CrSBr flakes of different thicknesses in the visible light range. Using micro-reflectance spectroscopy, we measured the optical contrast of thin CrSBr flakes with respect to different substrates. The complex refractive index was extracted by modeling the optical contrast with the Fresnel equations. We extracted the band gap values of CrSBr in the few-layer limit. We determined the band gaps for monolayer, bilayer, and trilayer CrSBr to be 1.88 eV, 1.81 eV, and 1.77 eV, respectively. As a comparison, the band gap for multilayer CrSBr is outside our measured range, that is, below 1.55 eV. Our results suggest that the band gap of CrSBr decreases as thickness increases.

Birefringence mapping of biological tissues based on polarization sensitive non-interferometric quantitative phase imaging technique

ObjectiveOral cancer is a leading cause of mortality globally, particularly affecting developing regions where oral hygiene is often overlooked. The optical properties of tissues are vital for diagnostics, with polarization imaging emerging as a label-free, contrast-enhancing technique widely employed in medical and scientific research over past few decades. Materials and methodsWe present a novel polarization sensitive quantitative phase imaging of biological tissues by incorporating the conventional polarization microscope and transport of intensity equation-based phase retrieval algorithm. This integration provides access to the birefringence mapping of biological tissues. The inherent optical anisotropy in biological tissues induces the polarization dependent refractive index variations which can provide the detailed insights into the birefringence characteristics of their extracellular constituents. Experimental investigations were conducted on both normal and cancerous oral tissue samples by recording a set of three polarization intensity images for each case with a step size of 2 μm. ResultsA noteworthy increment in birefringence quantification was observed in cancerous as compared to the normal tissues, attributed to the proliferation of abnormal cells during cancer progression.The mean birefringence values were calculated for both normal and cancerous tissues, revealing a significant increase in birefringence of cancerous tissues (2.1 ± 0.2) × 10−2 compared to normal tissues (0.8 ± 0.2) × 10−2. Data were collected from 8 patients in each group under identical experimental conditions. ConclusionThis polarization sensitive non-interferometric optical approach demonstrated effective discrimination between cancerous and normal tissues, with various parameters indicating elevated values in cancerous tissues.

RF sputtered metal oxide layers as ARCs to improve photovoltaic performance of commercial monocrystalline solar cell

The rf-sputtered ZnO, MgO and Al2O3 transition metal oxide nano layers were developed as efficient antireflection coatings (ARCs) on commercial monocrystalline silicon (m-Si) photovoltaic cells. Wavelength dependence reflectance measurements show minimal reflectance (i.e., ∼1.3–2.0%) between 350 and 800 nm wavelength regions affirming antireflection behavior of oxide layers. The phase formation studies of these oxide layers display the crystalline phase however the presence of non-crystalline phase is noted in Al2O3 diffractogram pattern. Cross section microstructure characterization carried out using scanning electron microscopy (SEM) to know the ARC layer thickness illustrates MgO, ZnO and Al2O3 layers with coating thickness around 85 nm, 87 nm and 77 nm respectively. Also, the thickness of antireflection coatings computed using wavelength dependent refractive index measurement is consistent with cross section microstructure images. Photon to energy conversion (PEC) of ARC coated device under 1 sun condition display 1.99%, 1.07% and 0.39% improvement in efficiencies compared with commercial m-Si-solar cell endorsing suitability of selected transition metal oxides as efficient ARC materials. The external quantum efficiency (EQE) measurements show notable improvement in efficiency for MgO, ZnO and Al2O3 coated devices reaffirming their usability as efficient ARC materials on commercial m-Si-solar cells.

Surface-phonon-polariton-enhanced photoinduced dipole force for nanoscale infrared imaging.

The photoinduced dipole force (PiDF) is an attractive force arising from the Coulombic interaction between the light-induced dipoles on the illuminated tip and the sample. It shows extreme sample-tip distance and refractive index dependence, which is promising for nanoscale infrared (IR) imaging of ultrathin samples. However, the existence of PiDF in the mid-IR region has not been experimentally demonstrated due to the coexistence of photoinduced thermal force (PiTF), typically one to two orders of magnitude higher than PiDF. In this study, we demonstrate that, with the assistance of surface phonon polaritons, the PiDF of c-quartz can be enhanced to surpass its PiTF, enabling a clear observation of PiDF spectra reflecting the properties of the real part of permittivity. Leveraging the detection of the PiDF of phonon polaritonic substrate, we propose a strategy to enhance the sensitivity and contrast of photoinduced force responses in transmission images, facilitating the precise differentiation of the heterogeneous distribution of ultrathin samples.

Dependence of refractive index of Zamzam, bottled drinking, and distilled waters on temperature and wavelength: a simple approximation using computer simulation phase shifting digital interferometry

Dependence of refractive index of Zamzam, bottled drinking, and distilled waters on temperature and wavelength: a simple approximation using computer simulation phase shifting digital interferometry

Impact of Sn-doping on the optoelectronic properties of zinc oxide crystal: DFT approach.

This study aims to provide a concise overview of the behavior exhibited by Sn-doped ZnO crystals using a computational technique known as density functional theory (DFT). The influence of Sn doping on the electronic, structural, and optical properties of ZnO have been explored. Specifically, the wavelength dependent refractive index, extinction coefficient, reflectance, and absorption coefficient, along with electronic band gap structure of the Sn doped ZnO has been examined and analyzed. In addition, X-ray diffraction (XRD) patterns have been obtained to investigate the structural characteristics of Sn-doped ZnO crystals with varying concentrations of Sn dopant atoms. The incorporation of tin (Sn) into zinc oxide (ZnO) has been observed to significantly impact the opto-electronic properties of the material. This effect can be attributed to the improved electronic band structure and optical characteristics resulting from the tin doping. Furthermore, the controllable structural and optical characteristics of tin-doped zinc oxide will facilitate the development of various light-sensitive devices. Moreover, the impact of Sn doping on the optoelectronic properties of ZnO is thoroughly investigated and documented.

Dependence of tetragonal barium titanate spontaneous polarization and refractive indices on DFT exchange-correlation functionals

The present work aims to use the Quantum Espresso software to theoretically investigate the spontaneous polarization and refractive indices of barium titanate (BaTiO3) in its tetragonal phase, and their dependence on the considered DFT exchange-correlation functionals. Among the functionals implemented in Quantum Espresso, twenty-four functionals were considered. The calculations, in which pseudopotentials of type ultrasoft were used, show that the values of all studied magnitudes depend on the used exchange-correlation functional. According to the obtained results, for the considered functionals, it appears that there is a linearity between the spontaneous polarization and the ionic shift difference Δz(Ti)-Δz(Oz); this linearity can be explained by the fact that the dipolar interaction Ti-Oz is the main contributor to the spontaneous polarization, being seen that: (i) the spontaneous polarization is a consequence of the coupling between the displacements of the constituent ions and their effective charges, (ii) the ionic shifts lead to a decrease in the Ti-Oz distance and an increase in the Ti-Ox and Ti-Oy distances, and then an increase in the Ti-Oz dipolar interaction compared to the Ti-Ox and Ti-Oy dipolar interactions, and (iii) the Ti and Oz ions possess the highest Born effective charges (in absolute values), in the polar direction, compared to the other ions, as reported in the literature. However, the closest values of the spontaneous polarization to the experimental data were obtained for the exchange-correlation functionals VDW-DF-C09, PZ, VDW-DF-CX, VDW-DF3-OPT1, VDW-DF2-C09, WC, and PBESOL. For these functionals, the refractive indices of ordinary and extraordinary polarizations were studied as a function of the light wavelength, in the range 160–940 nm. The obtained results show that the behavior of both refractive indices with respect to the wavelength, for visible light, is quit similar to that of Sellmeier equation with good agreement with the experimental data, particularly for the van der Waals functionals VDW-DF3-OPT1, VDW-DF-CX, VDW-DF2-C09, and VDW-DF-C09.

Refractive index dependence of the radiative rate of a magnetic dipole transition for a nanoparticle system

The emission spectra of Cs2NaEuCl6 nanoparticles (NPs) synthesized by the hot injection method are interpreted. Dispersion of the NPs in alkane solvents experimentally enables the magnetic dipole radiative rate in vacuum for the 5D0 - 7F1 channel to be determined as 14.7 ± 0.1 s−1, in agreement with the calculated value.

Separation of an Industrial Mixture of Decalin or Naphthalene Fluorination Products: Cis-Perfluorodecalin, Trans-Perfluorodecalin and Perfluoro(butylcyclohexane): Physicochemical, Thermophysical, and Spectral Data

New physicochemical data for trans-perfluorodecalin (trans-PDF) and cis-perfluorodecalin (cis-PFD) are presented. Based on the differential scanning calorimetry, the temperature and heat of the solid−liquid phase transition are determined. The coefficients of Antoine’s equation are calculated based on the experimental temperature–pressure dependence data. This article also presents data on the rheological properties («zero» shear viscosity and apparent activation energy for the viscous flow) of the studied compounds. The dependencies of refractive index and excess volume (density) on temperature are studied. Gas chromatography–mass spectrometry data and FTIR, 13C NMR, and 19F NMR spectra are provided. The dependencies are given for the perfluoro(butylcyclohexane) (BCH)–trans-PFD, BCH–cis-PFD, and trans-PFD–cis-PFD binary systems and BCH–trans-PFD–cis-PFD ternary system: refractive index and density (liquid molar volume and excess molar volume) of composition and temperature. The dependences of the excess molar volume on the composition and temperature of the mixtures are correlated with Redlich-Kister and Kohler equations.

GaN film optical nonlinearity: wavelength dependent refractive index for All-Optical switching application

Gallium Nitride (GaN) is fast becoming a potential replacement for silicon in complex electronic and photonics circuitries and systems. At higher optical intensity, optical effects such as non-linear effects would become non-trivial. To this end, we investigated nonlinear optical properties of metal–organic chemical vapor deposited GaN. Specifically, continuous-wave laser Z-scan techniques were employed to obtain nonlinear refractive index, n2, of a 1-µm thin layer on a c-plane sapphire substrate. FESEM, PL, XRD and EDS analysis confirmed the good quality growth of GaN thin film. We detected a reversal of polarity of the n2 value at 637 nm and 405 nm of CW laser excitation and femtosecond laser pulse at 808 nm. This is substantiated by theoretical calculation of GaN’s n2 showing sign switchover at wavelength shorter than 420 nm. This presents a new all-optical switching scheme based on the switchover of wavelength dependent n2. These findings point to opportunities for GaN-based integrated photonics for nonlinear and quantum photonics applications.

Anionic framework descriptors and microstructure affects on optical parameters of Ag7+x(P1-xGex)S6 single crystals

Herein we present a detailed study of single crystalline samples of Ag7+x(P1-xGex)S6 (x = 0, 0.1, 0.25, 0.33, 0.5, 0.75, 1) solid solutions. The Ag7+x(P1-xGex)S6 crystals were grown by directional crystallization from melt and characterized by techniques of XRD, Raman scattering, optical transmission measurements, spectral ellipsometry and electron microscopy. XRD and Raman scattering indicates a formation of solid solutions. The spectral dependences of refractive index are nonlinear with a maximum at the spectral range of ∼645–820 nm. It has been established, that P5+→Ge4+ cationic substitution leads to a monotonic nonlinear increase in the refractive index n from 2.58 (x = 0) to 2.75 (x = 1). The obtained values of refractive index were used to describe the optical parameters by the Wemple-DiDomenico equation. The spectral dependences of lnα at all studied temperatures (77–300 K) have an exponential shape near the absorption edge, indicating that they obey Urbach's rule. The corresponding value of the pseudo-gap Eg* and Urbach energy EU were determined. Increasing the Ge content in solid solutions causes a decrease in Eg* (1.971–1.466 eV) and EU (179.46–21.90 meV) values. Revealed Eg* values suggest that single crystalline Ag7+x(P1-xGex)S6 might be used as perspective solar harvesting materials. The practical application of these materials can be further enhanced with the results of temperature studies of variations of Eg* values. The changes in optical parameters are explained based on the structural and microstructural parameters of the studied solid solutions.

Nonlinearity shaping in nanostructured glass-diamond hybrid materials for optical fiber preforms

Nanodiamond integration with optical fibers has proved a compelling methodology for magneto-optics. We reveal that the applicability of nanodiamonds in nonlinear optics goes beyond the previous demonstrations of frequency converters. Instead, we exploit the recently reported volumetric integration of nanodiamonds along the optical fiber core and show that the nonlinear response of glasses can be manipulated by nanodiamonds. By taking the mature z-scan approach we measure the nonlinear absorption and nonlinear refraction of three dielectric materials containing nanodiamonds in different concentrations and sizes. The work begins with nanodiamond-water suspensions, which offer the advantage of rapidly assessing the dependence of the nonlinear refractive index on the nano-particle concentration and size. Subsequently we investigate two fiber preforms based on silica and soft glass doped with nanodiamonds to evaluate the feasibility of nonlinearity shaping. We achieve a nearly 20% reduction of the nonlinear refractive index of fused silica containing trace amounts of nanodiamonds relative to a pristine reference. The demonstration of such a noticeable impact on the nonlinear response of the key optical material widely accepted by ultrafast optics practitioners provides a guideline for future work on the novel concept of negative nonlinearity fibers, which could disrupt the established chromatic dispersion-nonlinearity landscape.

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-insensitive label-free SARS-CoV-2 spike protein detection based on complementary refractive index and temperature dependence of multi-mode interference and grating resonance

We demonstrated temperature-insensitive, label-free detection of SARS-CoV-2 spike protein (SSP) by harnessing the complementary refractive index and temperature dependence of multi-mode interference (MMI) created by a no-core fiber (NCF) and phase-matched resonance generated by a long-period fiber grating (LPFG). To combine MMI and grating resonance, primarily sensitive to the surrounding medium refractive index (SMRI) and ambient temperature, respectively, a fiber-optic transducer was fabricated by splicing an NCF segment with an LPFG inscribed on double-clad fiber. The transducer was functionalized with human ACE2 receptors to selectively capture SSP. The functionalized sensor head exhibited high SSP selectivity, with overall average wavelength displacements of ∼253.33 and ∼160.00 pm in PBS and saliva, respectively, for SSP with concentrations ranging from 1 to 104 ng/mL. These spectral shifts are associated with localized SMRI modulations on the sensor surface induced by specific binding between SSP and ACE2. We also examined the cross-reactivity of the sensor head for MERS-CoV spike protein to confirm its SSP specificity. Moreover, we proved the capability of temperature-independent SSP detection and ambient temperature measurement by scrutinizing the temperature effect on the sensor performance. Our functionalized fiber transducer showed great promise as a temperature-insensitive and portable platform for rapid SSP detection.

PROSPECULAR: A model for simulating multi-angular spectral properties of leaves by coupling PROSPECT with a specular function

Understanding the optical properties of leaves is of great importance for characterizing the relationships between leaf traits and remote sensing signals. The relationship between biochemical parameters and leaf spectral reflection has been widely established through PROSPECT, while surface structural parameters can be linked to leaf multi-angular reflection through Bidirectional Reflectance Distribution Function (BRDF) models. However, it's still challenging to characterize how leaf spectra response changes with different illumination and viewing geometries, in connection to both biochemical and surface structural traits. To address this challenge, we propose the model PROSPECULAR, which combines PROSPECT with a specular function determined by illumination-viewing geometry parameters, wavelength-dependent refractive index, and roughness. This model simulates spectral and multi-angular BRF and retrieves both leaf biochemical and surface structural parameters. The PROSPECULAR accounts for the wavelength dependence of the leaf surface refractive index in the specular function and separates the specular reflection from PROSPECT in the diffuse component calculation. The accuracy of PROSPECULAR's spectral simulation was assessed using a multi-angular dataset measured in the hemispherical space (42 viewing zenith angles (VZAs) at 20–50° source zenith angles (SZAs)). Then, the inversion accuracy of PROSPECULAR was validated using a multi-angular dataset measured in the principal plane (13 VZAs and 20–50° SZAs). The results showed that PROSPECULAR was able to simulate multi-angular BRF (RRMSE = 16.27%) when SZA was <50° and retrieve a unified set of biochemical parameters for each leaf sample using multi-angular BRF (RMSE of chlorophyll, water, dry matter, protein, and carbon-based constituents were 11.31 μg/cm2, 0.0029 g/cm2, 0.0022 g/cm2, 0.00096 g/cm2, and 0.0028 g/cm2, respectively). The agreement between the calculations and measurements of multi-angular BRF for various plant species indicated that PROSPECULAR is an effective leaf optical model. In contrast, the existing radiative transfer models (PROSPECT, PROCWT, PROCOSINE, and PROSDM) showed varying levels of accuracy in inverting biochemical parameters, depending on the VZA. The advantage of PROSPECULAR is its potential for characterizing both spectral and directional properties of leaves at arbitrary given illumination-viewing geometry and inverting leaf parameters using BRF data from several VZAs in the hemispherical space.

The Dependence of the Nonlinear Refractive Index of Laser and Optical Glasses on Their Optical Constants

The Dependence of the Nonlinear Refractive Index of Laser and Optical Glasses on Their Optical Constants

Theoretical investigation on the linear and nonlinear optical properties of DAPSH crystal

The linear polarizability, first and second hyperpolarizabilities of the asymmetric unit of DAPSH crystal are studied and compared with available experimental results. The polarization effects are included using an iterative polarization procedure, which ensures the convergence of the dipole moment of DAPSH embedded within a polarization field generated by the surrounding asymmetric units whose atomic sites are considered as point charges. We estimate macroscopic susceptibilities from the results of the polarized asymmetric units in the unit cell, considering the significant contribution of the electrostatic interactions in crystal packing. The results show that the influence of the polarization effects leads to a marked decrease of the first hyperpolarizability, compared with the respective isolated counterpart, which improves the concordance with the experiment. There is a minor influence of polarization effects on the second hyperpolarizability but our estimated result for the third-order susceptibility, related to the NLO process of the intensity dependent refractive index, is significant as compared with the results for other organic crystals, such as chalcone-derivatives. In addition, supermolecule calculations are conducted for explicit dimers in presence of the electrostatic embedding to illustrate the role played by the electrostatic interactions in the hyperpolarizabilities of the DAPSH crystal.

Mode Dependence of Refractive Index Sensitivity of Long-Period Fiber Gratings Induced by Periodically Embedded Multimode Fiber

In this paper, we present and verify the mode dependence of refractive index (RI) sensitivity of long-period fiber grating induced by periodically embedded multimode fiber (PEM-LPFG). The PEM-LPFG is firstly fabricated by periodically embedding multimode fiber (MMF) into the single mode fiber (SMF). The resonant mode is translated by reducing the cladding. Numerical simulations based on beam propagation method (BPM) are applied to calculate the transmission spectrum, mode distribution, and RI sensitivities of the PEM-LPFG. The cladding diameter after etching is determined to be 89 μm and 68 μm, which corresponds to the mode translated from LP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">012</sub> to LP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">07</sub> and LP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">05</sub> , respectively. The experimental results indicate that the maximum refractive index sensitivity of 1322.26 nm/RIU in the range of 1.333 -1.437 RIU is achieved when the resonant mode is LP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">07</sub> , which is 4 times as large as the original one (325.58 nm/RIU @ LP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">012</sub> mode). PEM-LPFG working at LP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">05</sub> mode exhibits a lower sensitivity of 844.72 nm/RIU. All of the experimental results are in good agreement with the simulation. The RI sensitivity optimization of PEM-LPFG is able to realize by mode converting. Furthermore, the temperature responses are measured to be 13 pm/°C and 4 pm/°C. This work provides a theoretical reference and experimental evidence for the dependence of the PEM-LPFG RI sensitivity on the resonant mode for the first time.