Wavelength Dependence Of Refractive Index Research Articles

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.

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.

Effect of Nickel doping on the Structural, Optical, and electrical properties of titanium dioxide thin films for the application of sensing devices

Thin films of pristine titanium dioxide (TiO2) and doped with different concentrations (0–8) at.% of nickel (Ni) were synthesized onto transparent glass substrates using the spray pyrolysis deposition technique. Field emission scanning electron microscopy revealed the porous and agglomerated surface morphology of the films. X-ray diffractometer demonstrated the anatase crystal structure with a nominal increment of (101) peak. The shifting of peak position revealed the expansion of the unit cell volume from 134.64 to 137.54 (Å)3 whereas crystallite size increased from 34 to 63 nm. Using the Fizeau fringes technique, the thickness of the films was determined between 165 and 190 nm. UV–Vis measurements were employed to examine the optical characteristics of the films. The red shift was observed for 2 at.% Ni content (3.38 eV) while the blue shift was observed for (4–8) at.% Ni content. The wavelength-dependent refractive index and dielectric constant showed anomalous dispersion in the absorption band, representing the transparency of the films. The 4-point probe measurement showed a decreasing trend of resistivity with increasing temperature, whereas the resistivity increased with Ni content. Activation energy indicated a higher amount of adsorbed oxygen in the films due to the high amount of Ni content.

Impact of wildfires on regional ozone and PM2.5: Considering the light absorption of Brown carbon

The influence of wildfire brown carbon (BrC) in moderating the formation of O3 and fine particulate matter (PM2.5) due to its absorption of ultraviolet (UV) radiation is, for the first time, investigated using a modified community multiscale air quality (CMAQ) model. The wavelength-dependent imaginary refractive index of the organic carbon from wildfires, which are needed by the CMAQ model for its inline photolysis rate calculation, are generated experimentally from wood burning aerosols from a combustion chamber. On high emission days of the Bastrop County Complex fire in Texas in early September 2011, BrC UV absorption reduces the daytime average NO2 photolysis rate by up to 38% in the core region of the wildfire plume compared to the base scenario that does not consider BrC absorption. Consequently, O3 production in the smoke plume is suppressed compared to the base scenario due to reduced HOx radical concentrations. In the core region, the predicted O3 increase due to wildfire reaches as high as 47–123 ppb without considering BrC absorption, the predicted increase of O3 is 5–15% lower when BrC absorption is considered. Similarly, considering the BrC UV absorption leads to approximately 1% (or ∼2–3 μg m−3) lower estimation of the wildfire emissions’ impact on total PM2.5. This change is small because secondary aerosols, which are the components affected by BrC absorption, only account for a small fraction of the total PM2.5 in wildfire impacted regions in this study. In addition, our study shows that assumptions about aerosol mixing state (core-shell vs. homogeneous) in the inline photolysis rate calculation would not significantly affect out assessment of the impact of wildfire BrC light absorption on O3 and PM2.5.

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.

Interaction of a photon with the surface and the bulk potentials of dielectric medium and a relativistic wave equation describing reflection and refraction phenomena and material dispersion

The surface potential differs from that of bulk, due to different atomic structures and vibration modes of a solid. Interaction of a photon with the potentials leads to material dispersion. Experimentally the surface and the bulk potentials can be determined from the wavelength-dependent refractive index. They are found to be the correlated quantities at different temperatures. A relativistic wave equation is proposed in this work, which contains the potentials. It provides a consistent description of reflection and refraction phenomena and material dispersion. Using this approach we investigate the surface and the bulk potentials of silica glass. The potentials decrease with rising temperature. The bulk potential increases with the density of the glass, whereas the surface potential remains almost unchanged at room temperature.

Wavelength-dependent elasto-optic tensor elements from acoustic Bragg diffraction

We report measurements of the elasto-optic constants p11 and p21 as a function of wavelength, for a variety of commercial glasses. The measurements were made using an apparatus based on the Dixon–Cohen design, in which the intensity of light diffracted from an acoustic pulse train is used to extract the elasto-optic tensor, using also data on the index of refraction and speed of sound. A variety of glass compositions were studied, and characterized compositionally using electron microprobe analysis; mechanically using speed of sound measurements; optically, via wavelength-dependent index of refraction; and structurally, using Raman and NMR spectroscopies. The final elasto-optic data were fit using the Wemple–DiDomenico model, and the results interpreted in terms of the effective band gap and deformation potentials, which were found to be sensitive to the different chemical bonds found in the glasses.

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.

Fuel classification and adulteration detection using a highly sensitive plasmonic sensor

In this paper, a plasmonic refractive index sensor is proposed based on a square ring-type resonator with gratings, which is coupled with a straight metal-insulator-metal (MIM) waveguide that has two triangular stubs. The adulteration of fuel may have detrimental effects on a variety of systems, including automobiles, people's health, and even the environment, in addition to reducing fuel economy. That is why this sensor has been designed for classifying different types of fuels and detecting the extent of adulteration in fuel. The finite element method (FEM) has been applied for numerical analysis of the structure. The sensor monitors the changes in the resonant wavelength and how light passes through the resonator to figure out the unknown material's refractive index. The sensor exhibits high sensitivity, and the maximum achievable sensitivity is 3270.3 nm/RIU with a figure of merit (FOM) of 31.154, when the refractive index of the dielectric is 1.01 and the sensor is functioning in mode-4. For mode-1, both the FOM and the quality factor are found to have their highest values, 45.28 and 46.508, respectively. According to the simulation results for different ranges of refractive index, when analyzing values between 1.3 and 1.4, the sensitivity reached its peak at 3138.8 nm/RIU. This means that while operating in mode-4, it is suitable for use in bio-sensing applications. Furthermore, our new sensor can detect change in the temperature in a broad spectral range using the wavelength-dependent refractive index of ethanol with a maximum achievable temperature sensitivity of 1.159 nm/°C.

Etalon-Assisted Determination of the Complex Index of Refraction of a Solution for the Study of Strong Cavity-Vibrational Coupling of PF6- in Acetonitrile.

A new method is established using an etalon cavity to assist in the determination of the wavelength-dependent complex index of refraction of a solution throughout the mid-infrared range. The results are used to study the cavity-vibration polaritons of PF6- in acetonitrile. Mixed states are formed by placing solution inside a pair of parallel plate mirrors with a wavelength-scale spacing, i.e., within an etalon, such that there are cavity states that are angle-tuned into resonance with the strong P-F vibrations. The dominant ν3 vibrations of PF6- consist of nearly triply degenerate oscillations of the partial-positively charged phosphorous against antisymmetric concerted motions of different sets of fluorine atoms with partial negative charges. These vibrations are dominant even though the solute is 29 times less concentrated than the solvent on a molar basis. The first part of the paper describes the method of determining the complex index of refraction of the solution from a combination of etalon transmission maxima and the attenuated total reflection (ATR) absorption spectrum of the solution. The results are presented as an analytical function including a sum of 37 vibrational contributions. Absolute integrated isolated band intensities were determined to be 463 ± 4, 462 ± 7, and 266 ± 4 km/mol for the three ν3 PF6- vibrations at 841.4, 847.4, and 854.0 cm-1, respectively, which sum to 1191 ± 9 km/mol for the ν3 band. Then, the results are used to simulate the measured etalon transmission using the transfer matrix (TM) method with and without the ν3 target vibrations. The etalon transmission simulations reconstruct the position of cavity modes in the absence of target vibrations. They provide input data for the testing of simple quantum mechanical models for the interaction of vibrations with cavity modes and the interactions of vibrations with other vibrations within the molecule and between solute and solvent. The model shows that the nearly degenerate ν3 vibrations interact with each other with a vibration-vibration coupling of 33 ± 5 cm-1. This is comparable to the cavity-vibration coupling of 30.4 ± 2.9 cm-1 of the two strongest vibrations of PF6-.

Optical Epidermal Mimicry from Ultraviolet to Infrared Wavelengths.

Optical tissue phantoms present substantial value for medical imaging and therapeutic applications. We have developed an epidermal tissue phantom to mimic the optical properties of human skin from the ultraviolet to the infrared region, exceeding the breadth of existing studies. An epoxy matrix is combined with melanin-mimicking polydopamine via a cost-effective fabrication strategy. Reflectance and transmittance measurements enable calculation of the wavelength-dependent complex refractive index and absorption coefficient. Results are compared with literature data to establish agreement with a real human epidermis. By analyzing emissive power at a typical skin temperature, the epidermal tissue phantom is shown to accurately mimic the radiative properties of human skin. This simple, multifunctional material represents a promising substitute for human tissue for a variety of medical and bioengineering applications.

Optical determination of layered-materials InSe thickness via RGB contrast method and regression analysis

Indium selenide (InSe) features intriguing thickness-dependent optoelectronic properties, and a simple, and precise way to identify the thickness is essential for the rapid development of InSe research. Here, a red, green, and blue (RGB) color contrast method with regression analysis for quantitative correlation of three optical contrasts from RGB channels with the InSe thickness (1–35 nm), is demonstrated. The lower accuracy of the thickness identification obtained from the individual channels was discussed. Moreover, the effective refractive indices in the three RGB regions can be extracted from the Fresnel equation and numerical analysis by finding the best fit to the experimental optical contrast. After further consideration of the wavelength-dependent refractive indices, the slope of the regression line between the estimated thickness and that obtained from the atomic force microscope was improved from 1.59 ± 0.05 to 0.97 ± 0.02. The complex refractive index spectra of InSe (1–10 layers) generated from ab initio numerical calculation results were also adopted to identify the InSe thickness. Compared to dispersion, the evolution of the band structure had less effect on thickness identification. This work could be extended to other layered materials, facilitate the thickness-dependent study of layered materials, and expedite the realization of their practical applications.

Ellipsometry-transmission measurement of the complex refractive indices for a series of organic solvents in the 200–1700 nm spectral range

Organic solvents are fluids commonly used in different branches of materials science. The determination of the wavelength-dependent complex refractive index of organic solvents is essential in physical, chemical, biological, and optical applications. The existing databases for the complex refractive index of many organic solvents are insufficient and have low accuracy, particularly in the ultraviolet (UV), visible (Vis), and near-infrared (NIR) spectral ranges. In this work, using spectroscopic ellipsometry combined with the transmission method, the complex refractive indices of isopropyl acetate (IPAC), dimethyl sulfoxide (DMSO), N, N-dimethylformamide (DMF), N, N-dimethylaniline (DMA), dichloromethane (DCM), tetrahydrofuran (THF), P-Xylene (PX), and ethyl acetate (EA) were measured in the spectral range 200–1700 nm at room temperature and ambient pressure. The refractive index and absorption index were measured by the ellipsometry and transmission method, respectively, allowing accurate measurement of the complex refractive index of materials with weak optical absorption. Based on these experimental data, the refractive indices in the weak absorption waveband were fitted using Cauchy’s dispersion formula. According to the dispersion relationships and molecular structure of each solvent, it is known that the addition of benzene rings, sulfur atoms, chlorine atoms, nitrogen atoms, and epoxides can increase the refractive index of a material. The results obtained in our laboratory for organic solvents provide evidence that the ellipsometry-transmission method is a promising technique for characterizing the optical constants of different types of materials. The experimental data of the complex refractive indices and their dispersion of organic solvents can provide a reference for its practical applications.

Polarimetric investigation of selected cloud compositions in exoplanetary atmospheres

Aims. We investigated the impact of selected cloud condensates in exoplanetary atmospheres on the polarization of scattered stellar radiation. Methods. We considered a selection of 25 cloud condensates that are expected to be present in extrasolar planetary atmospheres. Using the three-dimensional Monte Carlo radiative transfer code POLARIS and assuming Mie scattering theory, we calculated and studied the net polarization of scattered radiation as a function of planetary phase angle at optical to near-infrared wavelengths (0.3 μm to 1 μm). Results. In addition to the well-known characteristics in the state of polarization, such as the rainbow determined by the real part of the refractive index, the behavior of the underlying imaginary part of the refractive index causes an increase or decrease in the degree of polarization and a change of sign in the polarization at a characteristic wavelength. In contrast to Al2O3 and MgFeSiO4, clouds composed of SiO, MnS, Na2S, or ZnS produce a rapidly decreasing degree of polarization with increasing wavelength in the context of an exoplanetary atmosphere. Furthermore, the sign of the polarization changes at a wavelength of about 0.5 μm to 0.6 μm, depending on the specific cloud condensate. The resulting net polarization is mainly positive for cloud compositions with large imaginary parts of the refractive index, such as Fe, FeS, and FeO. In addition, for Fe and FeS clouds, the maximum degree of polarization at long wavelengths is shifted to larger phase angles than for FeO. Conclusions. We found that most of these cloud condensates, such as chlorides, sulfides, or silicates, are distinguishable from each other due to their unique wavelength-dependent complex refractive index. In particular, an increase or decrease of the net polarization as a function of wavelength and a change of sign in the polarization at specific wavelengths are important features for characterizing cloud compositions in exoplanetary atmospheres.

Refractive index dispersion of BGa(As)P alloys in the near-infrared for III-V laser integration on silicon

BxGa(1−x)P and BxGa(1−x)AsyP(1−y) alloys are of potential interest in III-V heterostructures for integration with silicon. Waveguide design utilizing these alloys requires an understanding of the refractive index properties and their variation with composition. Refractive index dispersion was measured and modeled in the wavelength range of 827–2254 nm using spectroscopic ellipsometry at room temperature for samples with boron and arsenic fractions from 0% to 6.6% and 0% to 17%, respectively. The refractive index was found to increase with increasing boron composition as a result of strain due to lattice constant mismatch with the silicon substrate. For the arsenic-containing alloy, the refractive index was found to increase independently of strain. An empirical model based on the composition dependent variation of Cauchy dispersion function coefficients was developed for BGaAsP alloys lattice matched to silicon at the growth temperature. This model can be used to calculate the wavelength dependent refractive index of lattice matched boron and arsenic combinations for applications in semiconductor waveguides, an example of which is proposed. The results of this study are of interest more broadly for other III-V on silicon applications including photovoltaics and more generally in terms of the ellipsometric investigations of thin films on non-native substrates.

A semi-empirical correction for the Rayleigh-Debye-Gans approximation for fractal aggregates based on phasor analysis: Application to soot particles

The Rayleigh Debye-Gans approximation for Fractal Aggregates (RDG-FA) is commonly used for the evaluation of the radiative properties of fractal aggregates of nanometer-scale nearly spherical particles as soot particles. The cost of its simplicity, however, is the precision of the aggregate cross sections when the refractive index deviates from unity and when the aggregate’s spheres, or monomers, are not sufficiently small compared to the wavelength. While correction factors have been highlighted before, their physical origin is not clear and no universal correction factors are proposed. The present study develops an approach based on phasor analysis of the aggregate’s internal electric field rigorously determined by the discrete dipole approximation. Aggregates representative of the Diffusion Limited Cluster Aggregation (DLCA) regime having a fractal dimension of Df=1.78 are considered as representative of a soot aggregate. The results reveal that correction factors to the RDG-FA for forward scattering (A) and the absorption cross section (h) are due to a competition between internal-field hot-spots caused by point contact between the spherical monomers and a decrease of the field amplitude as the field propagates through the aggregate. Both phenomena are neglected in the RDF-FA by definition. The absorption phenomenon explains the aggregate-size dependence of A and h. These effects are then studied as the aggregate size varies according to the number of monomers Nm ranging from 10 to 1000, as the monomer radius varies from Rm=5nm - 30nm, and as the wavelength varies from λ=266nm - 1064nm. Both constant and wavelength dependent refractive indices for organic, graphitic, and amorphous soot are considered. Finally, a semi-empirical model is proposed intended to correct the RDG-FA theory based on the analysis.

Refractive Index and Extinction Coefficient of Vapor-deposited Water Ice in the UV–vis Range

Abstract Laboratory results of the optical properties of vapor-deposited water ice, specifically the refractive index and extinction coefficient, are available mainly for a selective set of wavelengths and a limited number of deposition temperatures. Experimental limitations are the main reason for the lack of broadband data, which is unfortunate as these quantities are needed to interpret and predict astronomical and planetary observations. The goal of this work is to address these lacking data, using an experimental broadband method that is capable of rapidly providing reliable water ice data across the entire UV–visible range. This approach combines the simultaneous use of a monochromatic HeNe laser and a broadband Xe-arc lamp to record interference fringes of water ice during deposition at astronomically relevant ice temperatures. The ice thickness is typically more than 20 μm. Analyzing the period and intensity patterns combining both the monochromatic and broadband interference patterns allows the determination of the wavelength-dependent refractive index and extinction coefficient. We present accurate refractive index and extinction coefficient graphs for wavelengths between 250 and 750 nm and ices deposited between 30 and 160 K. From our data, we find a possible structural change in the ice in the 110–130 K region that has not been reported before. We also discuss that the data presented in this paper can be used to interpret astronomical observations of icy surfaces.

Optical and dielectric properties of MoO3 nanosheets for van der Waals heterostructures

Two-dimensional (2D) insulators are a key element in the design and fabrication of van der Waals heterostructures. They are vital as transparent dielectric spacers whose thickness can influence the photonic, electronic, and optoelectronic properties of 2D devices. Simultaneously, they provide the protection of active layers in the heterostructure. For these critical roles, hexagonal boron nitride (hBN) is the dominant choice due to its large bandgap, atomic flatness, low defect density, and encapsulation properties. However, the broad catalogue of 2D insulators offers exciting opportunities to replace hBN in certain applications that require transparent thin layers with additional optical degrees of freedom. Here, we investigate the potential of single-crystalline molybdenum oxide (MoO3) as an alternative 2D insulator for the design of nanodevices that require precise adjustment of the light polarization at the nanometer scale. First, we measure wavelength-dependent refractive indices of MoO3 along its three main crystal axes and determine the in-plane and out-of-plane anisotropy of its optical properties. We find that the birefringence in MoO3 nanosheets compares favorably with other 2D materials that exhibit strong birefringence, such as black phosphorus, ReS2, or ReSe2, in particular in the visible spectral range, where MoO3 has the unique advantage of transparency. Finally, we demonstrate the suitability of MoO3 for dielectric encapsulation by reporting linewidth narrowing and reduced inhomogeneous broadening of 2D excitons and optically active quantum emitters, respectively, in a prototypical monolayer transition-metal dichalcogenide semiconductor. These results show the potential of MoO3 as a 2D dielectric layer for manipulation of the light polarization in vertical 2D heterostructures.

Measurement report: Comparison of airborne, in situ measured, lidar-based, and modeled aerosol optical properties in the central European background – identifying sources of deviations

Abstract. A unique data set derived from remote sensing, airborne, and ground-based in situ measurements is presented. This measurement report highlights the known complexity of comparing multiple aerosol optical parameters examined with different approaches considering different states of humidification and atmospheric aerosol concentrations. Mie-theory-based modeled aerosol optical properties are compared with the respective results of airborne and ground-based in situ measurements and remote sensing (lidar and photometer) performed at the rural central European observatory at Melpitz, Germany. Calculated extinction-to-backscatter ratios (lidar ratios) were in the range of previously reported values. However, the lidar ratio is a function of the aerosol type and the relative humidity. The particle lidar ratio (LR) dependence on relative humidity was quantified and followed the trend found in previous studies. We present a fit function for the lidar wavelengths of 355, 532, and 1064 nm with an underlying equation of fLR(RH, γ(λ))=fLR(RH=0,λ)×(1-RH)-γ(λ), with the derived estimates of γ(355 nm) = 0.29 (±0.01), γ(532 nm) = 0.48 (±0.01), and γ(1064 nm) = 0.31 (±0.01) for central European aerosol. This parameterization might be used in the data analysis of elastic-backscatter lidar observations or lidar-ratio-based aerosol typing efforts. Our study shows that the used aerosol model could reproduce the in situ measurements of the aerosol particle light extinction coefficients (measured at dry conditions) within 13 %. Although the model reproduced the in situ measured aerosol particle light absorption coefficients within a reasonable range, we identified many sources for significant uncertainties in the simulations, such as the unknown aerosol mixing state, brown carbon (organic material) fraction, and the unknown aerosol mixing state wavelength-dependent refractive index. The modeled ambient-state aerosol particle light extinction and backscatter coefficients were smaller than the measured ones. However, depending on the prevailing aerosol conditions, an overlap of the uncertainty ranges of both approaches was achieved.

Optical Properties of CaNb2O6 Single Crystals Grown by OFZ*

CaNb2O6 single crystals with an orthorhombic columbite structure are grown via an optical floating zone (OFZ) method. The as-grown crystals are colorless and free of low-angle grain boundaries and inclusions. They are transparent (up to 62%) in the visible to the infrared region (400–1000 nm) and have a low absorption coefficient (α = 1.56). The bandgap is determined as a direct transition and Eg = 4.28 eV. The wavelength-dependent refractive index and extinction coefficient of the CaNb2O6 crystals are derived from the obtained T and α spectra. Their photoluminescence spectra exhibit a strong and broad emission band centered at 465 nm.