Optical Inhomogeneities Research Articles

Features of synthesis of ZnSe ceramics from nanopowders obtained using a high-power laser

The reasons for the occurrence of optical inhomogeneities in ZnSe or Fe:ZnSe ceramics, which were made from nanoparticles, obtained using a continuous wave ytterbium fiber laser, were investigated. Evaporation of ZnSe at T ≤ 900 ˚С results in formation of large pores (0.5 - 10µm) in the ceramics. When the material is oxidized by means of oxygen adsorbed from air onto the surface of nanoparticles, such refractory phases as ZnO and ZnSeO3 are formed. Even a low content of these phases ( < 1wt. %) results in formation of accumulations of small crystallites ( 0.2 - 3 μm) in the ceramics. Numerous pores and extended accumulations of small crystallites are optical non-uniformities that scatter and absorb light. Changes in the chemical composition and contamination of ZnSe during the production of nanopowders and ceramics turned out to be too small for such inhomogeneities to form.

Component-based SHGC determination of BIPV glazing for product comparison

Building-integrated photovoltaic (BIPV) systems are intrinsically designed to generate electricity and to provide at least one building-related function. When BIPV modules act as glazing products in windows, skylights or curtain walls, their ability to control the transmission of solar energy into the building must be characterised by a Solar Heat Gain Coefficient (SHGC) or g value (also known as Total Solar Energy Transmittance – TSET – or “solar factor”). For the comparison of BIPV glazing products consisting of one PV laminate and possibly further, conventional glazing layers separated by gas-filled cavities, the procedures documented in international standards for architectural glazing (e.g. ISO 9050 and EN 410) form a suitable starting point. Easily implemented modifications to these procedures are proposed to take both optical inhomogeneity (if relevant) and extraction of electricity from BIPV glazing units into account. Geometrically complex glazing and shading devices, and light-scattering glazing layers, are outside the scope of the proposed methodology; SHGC determination for obliquely incident solar radiation is also excluded. For these cases, the experimental calorimetric approach documented in [ISO 19467:2017; ISO 19467-2:2021] is recommended.The paper also presents results and conclusions from an implementation exercise and sensitivity study carried out by participants of the IEA-PVPS Task 15 on BIPV. The cell coverage ratio in the PV laminate, the thermal resistance offered by the glazing configuration, the choice of boundary conditions and the effect of extracting electricity were all identified as parameters which significantly affect the SHGC value determined for a given type of BIPV glazing. A practicable approach to accommodate the great variety of dimensions typical for BIPV glazing is also proposed. These findings should pave the way for modifying the existing component-based standards for architectural glazing to take the specific features of BIPV glazing into account.

Correlation between biological activity and physicochemical properties of sodium dodecylbenzenesulfonate in aqueous solutions

The purpose of this study was to establish a correlation between the effect of the pollutant content on the dimensional and physicochemical characteristics of the investigated solutions and its effect on aquatic organisms. To this end, the surface tension, electrical conductivity, pH, and redox potential of aqueous solutions of sodium dodecylbenzenesulfonate were measured in a wide concentration range (10–710–2 М). The change in the size and number of optical inhomogeneities was investigated using the small-angle reflection method in the micron range. In addition, the behavior of aquatic biological objects (Daphnia Magna) was studied in the investigated solutions. It was shown that the investigated concentration dependences (including the behavior of biological objects) are non-linear: they have either a stepped character or clearly expressed extremes and are well correlated with each other. A comfortable concentration range of sodium dodecylbenzenesulfonate for daphnia (all daphnia are active within 58 hours of the experiment) was established (0.018–0.037 mM). The correlation and nature of the concentration dependences indicate that at critical concentrations, structural rearrangements occur in sodium dodecylbenzenesulfonate solutions, not only the formation of micelles and pre-micelles, but also structural rearrangements of the solvent (water) itself. Thus, it has been experimentally shown that the change in the structure of water during interaction with pollutants can significantly affect both the physicochemical properties of aqueous solutions and the behavior of aquatic biological objects.

An Analytical Model of Light Scattering by Birefringent Polycrystalline Dielectrics Using Perturbation of Maxwell's Equations

AbstractPolycrystalline materials have shown promise in advanced optical applications because of their unique optical and mechanical properties. Most polycrystalline materials have non‐uniform optical properties due to residual porosity, secondary phases, and/or crystalline anisotropies (e.g., birefringence). These optical inhomogeneities manifest as scattering that reduces the transparency of the polycrystal. Even in the case of a single‐phase polycrystal with negligible porosity, birefringence scattering will always be present whenever the crystal is anisotropic (non‐cubic). Multiple models for predicting birefringence scattering have been suggested in the literature that are successful in describing scattering loss in specific material systems. Here a first‐principles model of birefringent scattering that is applicable to any single‐phase, unaligned transparent polycrystal is derived. The model can treat grain size distributions and is not limited to a specific material system. The derivation culminates in an equation that describes birefringence scattering coefficient spectra using the single‐crystal refractive index tensor and chord length distribution (measured from a representative polished surface micrograph). The model should be useful for designing materials and characterization. For example, it can be used to predict transmissions of transparent polycrystals for a range of grain sizes or to characterize the average grain size using a transmission measurement.

Morphological Features of SiO2 Nanofillers Address Poor Stability Issue in Gel Polymer Electrolyte-Based Electrochromic Devices.

Nanofillers' applicability in gel polymer electrolyte (GPE)-based devices skyrocketed in the last decade as soon as their remarkable benefits were realized. However, their applicability in GPE-based electrochromic devices (ECDs) has hardly seen any development due to challenges such as optical inhomogeneity brought by incompetent nanofiller sizes, transmittance drop due to higher filler loading (usually required), and poor methodologies of electrolyte fabrication. To address such issues, herein, we demonstrate a reinforced polymer electrolyte tailored through poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP),1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF4), and four types of mesoporous SiO2 nanofillers, porous (distinct morphologies) and nonporous, two each. The synthesized electrochromic species 1,1'-bis(4-fluorobenzyl)-4,4'-bipyridine-1,1'-diium tetrafluoroborate (BzV, 0.05 M), counter redox species ferrocene (Fc, 0.05 M), and supporting electrolyte (TBABF4, 0.5 M) were first dissolved in propylene carbonate (PC) and then immobilized in an electrospun PVDF-HFP/BMIMBF4/SiO2 host. We distinctly observed that spherical (SPHS) and hexagonal pore (MCMS) morphologies of fillers endowed higher transmittance change (ΔT) and coloration efficiency (CE) in utilized ECDs; particularly for the MCMS-incorporated ECD (GPE-MCMS/BzV-Fc ECD), ΔT reached ∼62.5% and CE soared to 276.3 cm2/C at 603 nm. The remarkable benefit of filler's hexagonal morphology was also seen in the GPE-MCMS/BzV-Fc ECD, which not only marked an astounding ionic conductivity (σ) of ∼13.5 × 10-3 S cm-1 at 25 °C, thus imitating the solution-type ECD's behavior, but also retained ∼77% of initial ΔT after 5000 switching cycles. The enhancement in ECD's performance resulted from merits brought by filler geometries such as the proliferation of Lewis acid-base interaction sites due to the high surface-to-volume ratio, the creation of percolating tunnels, and the emergence of capillary forces triggering facile ion transportation in the electrolyte matrix.

Helical polymers for dissymmetric circularly polarized light imaging.

Control of the spin angular momentum (SAM) carried in a photon provides a technologically attractive element for next-generation quantum networks and spintronics1-5. However, the weak optical activity and inhomogeneity of thin films from chiral molecular crystals result in high noise and uncertainty in SAM detection. Brittleness of thin molecular crystals represents a further problem for device integration and practical realization of chiroptical quantum devices6-10. Despite considerable successes with highly dissymmetric optical materials based on chiral nanostructures11-13, the problem of integration of nanochiral materials with optical device platforms remains acute14-16. Here we report a simple yet powerful method to fabricate chiroptical flexible layers via supramolecular helical ordering of conjugated polymer chains. Their multiscale chirality and optical activity can be varied across the broad spectral range by chiral templating with volatile enantiomers. After template removal, chromophores remain stacked in one-dimensional helical nanofibrils producing a homogeneous chiroptical layer with drastically enhanced polarization-dependent absorbance, leading to well-resolved detection and visualization of SAM. This study provides a direct path to scalable realization of on-chip detection of the spin degree of freedom of photons necessary for encoded quantum information processing and high-resolution polarization imaging.

Optical modeling of a radioisotope atmospheric chamber

Volatile radioisotopes represent a substantial health risk when released into the environment. To better understand the environmental fate of radioisotopes, the authors constructed a cylindrical steel-walled chamber to simulate the atmospheric processing of volatile radioactive gases. Optical modeling was performed for the properties of simulated sunlight in the chamber to better characterize atmospheric reaction studies. Optical simulations were performed using two wall materials (steel and thin-film silica) and validated against experimental measurements. This optical analysis methodology can be used to improve the fidelity of atmospheric models by accounting for optical inhomogeneities enabling a firmer grasp of radioisotopes’ environmental fate.Graphical abstract

VIS-NIR Diffuse Reflectance Spectroscopy System with Self-Calibrating Fiber-Optic Probe: Study of Perturbation Resistance.

We report on the comparative analysis of self-calibrating and single-slope diffuse reflectance spectroscopy in resistance to different measurement perturbations. We developed an experimental setup for diffuse reflectance spectroscopy (DRS) in a wide VIS-NIR range with a fiber-optic probe equipped with two source and two detection fibers capable of providing measurements employing both single- and dual-slope (self-calibrating) approaches. In order to fit the dynamic range of a spectrometer in the wavelength range of 460-1030 nm, different exposure times have been applied for short (2 mm) and long (4 mm) source-detector distances. The stability of the self-calibrating and traditional single-slope approaches to instrumental perturbations were compared in phantom and in vivo studies on human palm, including attenuations in individual channels, fiber curving, and introducing optical inhomogeneities in the probe-tissue interface. The self-calibrating approach demonstrated high resistance to instrumental perturbations introduced in the source and detection channels, while the single-slope approach showed resistance only to perturbations introduced into the source channels.

Modeling of optical inhomogeneities in Cr-=SUP=-2+-=/SUP=-:CdSe lasers with a moving active element

The work is devoted to modeling the heating of moving active elements from CdSe and estimates emerging optical inhomogeneities. Active elements in the form of a parallelepiped are considered, which rotated in a circle perpendicular to the generation axis. As a result of calculations, it was found that the temperature distribution in the active element that occurs during the operation of the laser can be represented as the sum of two components. The first component is formed due to the balance between heat emission in the active element due to pumping and heat removal from it, which leads to the appearance of an aberration, which is the sum of &amp;quot;tilt&amp;quot; and &amp;quot;defocusing&amp;quot;. The second component is formed directly during the passage of the pump spot through the active element, is determined only by the heat release density and is not related to the cooling method of the active element. It leads to the appearance of &amp;quot;Gaussian&amp;quot; aberration, the amplitude of this aberration is directly proportional to the power of heat emission and inversely proportional to the frequency of rotation of the active element. Keywords: mobile active elements, optical inhomogeneities of the refractive index, Cr2+:CdSe laser.

Исследование метрологических характеристик системы визуализации структуры биотканей в пространственно-модулированном излучении

The work is devoted to the study of the measurement accuracy of the spatial frequency domain imaging system for the detection and objective numerical evaluation of optical inhomogeneities in biological tissues. As a result of the initial stage of experimental studies on a stand simulating a spatial frequency domain imaging system, the operating range of spatial frequencies of illuminating irradiation modulation was determined, which ensures maximum reproducibility of the measurement results, and the possibility of achieving a relative measurement error of optical parameters of no more than 10% was shown

Моделирование оптических неоднородностей в Cr-=SUP=-2+-=/SUP=-:CdSe-лазерах с подвижными активными элементами

The work is devoted to modeling the heating of moving active elements from CdSe and estimates emerging optical inhomogeneities. Active elements in the form of a parallelepiped are considered, which rotated in a circle perpendicular to the generation axis. As a result of calculations, it was found that the temperature distribution in the active element that occurs during the operation of the laser can be represented as the sum of two components. The first component is formed due to the balance between heat emission in the active element due to pumping and heat removal from it, which leads to the appearance of an aberration, which is the sum of "tilt" and "defocusing". The second component is formed directly during the passage of the pump spot through the active element, is determined only by the heat release density and is not related to the cooling method of the active element. It leads to the appearance of "Gaussian" aberration, the amplitude of this aberration is directly proportional to the power of heat emission and inversely proportional to the frequency of rotation of the active element.

Transmission functions of transmissive multilayer inhomogeneous holographic photopolymer liquid crystal diffraction structures

A new analytical model of diffraction of quasimonochromatic light beams on spatially inhomogeneous multilayer diffraction structures formed in photopolymer material with nematic liquid crystals having smooth optical inhomogeneity in the thickness of layers is presented. It is shown that when an applied electric field isapplied to diffraction layers containing a photopolymer composition with a high proportion of liquid crystalline component, a transformation of the selective response with a significant shift in angular selectivity occurs

Influence of SHS Precursor Composition on the Properties of Yttria Powders and Optical Ceramics

This study looked at optimizing the composition of precursors for yttria nanopowder glycine-nitrate self-propagating high-temperature synthesis (SHS). Based on thermodynamic studies, six different precursor compositions were selected, including with excesses of either oxidant or fuel. The powders from the precursors of all selected compositions were highly dispersed and had specific surface areas ranging from 22 to 57 m2/g. They were consolidated by hot pressing (HP) with lithium-fluoride sintering additive and subsequent hot isostatic pressing (HIP). The 1 mm thick HPed ceramics had transmittance in the range of 74.5% to 80.1% @ 1μm, which was limited by optical inhomogeneity due to incomplete evaporation of the sintering additive. Two-stage HIP significantly improves optical homogeneity of the ceramics. It was shown that an excess of oxidizer in the precursor decreases the powders' agglomeration degree, which forms large pore clusters in the ceramics.

Study of Light Diffraction on Electrically Controlled Multilayer Inhomogeneous Structures with Smooth Optical Inhomogeneity Based on Photopolymerizing Compositions with Nematic Liquid Crystals

Study of Light Diffraction on Electrically Controlled Multilayer Inhomogeneous Structures with Smooth Optical Inhomogeneity Based on Photopolymerizing Compositions with Nematic Liquid Crystals

Generation of multiple photonic hooks in reflection mode

Generation of multiple photonic hooks (PHs) at THz region in reflection mode by a multi-dielectric structure that consists of periodical or aperiodical scatterer units on top surface of a reflection screen has been systematically studied. The study focuses on effects of geometric and optical parameters of the multi-dielectric structure on characteristics of the PHs generated, especially the bending angle. These geometric and optical parameters include spacing between adjacent scatterer units, length of reflection screen, as well as the size, refractive index and number of scatterer units. The results show that these geometric and optical parameters are key factors in tailoring the performance of the multiple PHs generated. The spacing determines bending direction of PHs and there exists a critical spacing value. Smaller than this critical value, the PHs generated bend outwards. Larger than this critical value, the PHs bend inwards. In addition, the spacing can be also used to effectively adjust the intensity and bending angle of the PHs. Screen length affects mainly PH's bending. The size and refractive index differences between scatterer units introduce additional optical inhomogeneity that leads to the generation of asymmetrical multiple PHs. Finally, the possibility of generation of an arrayed PHs in the reflection mode is demonstrated.

Array of photonic hooks generated by multi-dielectric structure

Generation of array of photonic hooks (PHs) by a multi–dielectric structure that consists of periodically arrayed scatterer units has been systematically studied. The study focuses on the effects of geometric and optical parameters of the multi–dielectric structure on the characteristics of generated PHs, especially their bending angles. These geometric and optical parameters include size, shape, refractive index and number of scatterer units, and their adjacent spacing. The results show that the spacing, size and refractive index play a predominant role in tailoring the performance of the PHs array, and the spacing affects mainly the characteristics of a pair of symmetrical PHs while the size and refractive index differences between scatterer units affect mainly those of asymmetrical PHs as a result of the introduction of optical inhomogeneity. In the aspect of scatterer shape, for a multi–dielectric structure that consists of some cylinders, as the light wave is incident parallel (perpendicular) to the cylinder axis, its scattering characteristics are similar to those of the multi–dielectric structure that consists of some cuboids (spheres). In particular, for a structure consisted of cylinders or cuboids with long length in the z direction, an intensive photonic nanojet is additionally generated and located between the paired PHs provided that the wave is incident perpendicular to the cylinder axis or the longest side of cuboid. In the aspect of scatterer unit number, the multi–dielectric structures of odd and even scatterer units generate PHs with different characteristics. The paired PHs generated by multi–dielectric structure with equal spacings always bend outward. However, the paired PHs may bend inward provided that the multi–dielectric structure is designed properly. We have also studied the features of 2D PHs array. The results show that the 2D PHs array displays similar features to the 1D case. The application potential of both 1D and 2D PHs arrays is evaluated.

Conjugate heat transfer analysis of laser-irradiated cylindrical-shaped biological tissue embedded with the optical inhomogeneity

The current study is associated with the numerical investigation of the thermal behavior of cylindrical-shaped biological tissue during laser-based photo-thermal therapy. The light-tissue interaction has been modeled using the transient radiative transfer equation (TRTE). The TRTE in a cylindrical coordinate system is solved using the modified discrete ordinate method to obtain the intensity distribution inside the biological tissue. The solution of TRTE is coupled with Pennes bio-heat transfer equation (BHTE) to understand the thermic response of biological tissue. The Pennes BHTE is solved using the finite volume method (FVM). The two different types of optical inhomogeneity (absorption and scattering inhomogeneity) are considered in the current study. The inhomogeneity's optical and thermophysical properties may be the same/different from the homogeneous biological tissue. This conjugate heat transfer problem (CHTP) is solved using the harmonic mean technique. First, the present result is verified with the data available in the literature. Subsequently, the effect of inhomogeneity's optical properties on the temperature distribution is investigated. A comparative study between the same and different thermophysical properties of the biological tissue and inhomogeneity is performed. This study will help to accurately model the thermal characteristics of the laser-irradiated biological tissue having different thermophysical properties than the inhomogeneity.

Calibration Methods of a Portable Polarizing System for Monitoring Optically Inhomogeneous Media

Theoretical aspects of methods for calibrating Stokes polarimeters are considered. The prospects and opportunities for implementing the presented methods for calibrating portable polarization systems used in biology and medicine are determined. Based on a comparative analysis, a method for calibrating a portable Stokes polarimeter for medical applications is proposed. The chosen method provides the smallest error in measuring the parameters of the Stokes vector for calculating the parameters of optical anisotropy and researching the polarization properties of biological tissues. A series of experimental research and statistical analysis of the spatial distributions of the polarization parameters of the calibration sample was carried out to use the results for forming the instrument matrix of the developed Stokes polarimeter during calibration.

Importance of optical homogeneity for high-quality transparent ceramics

Two types of transparent Y2O3 ceramics without including large scattering sources such as residual pores, one with very high optical homogeneity (type A) and another one with slightly insufficient optical homogeneity (type B), are purposely prepared, and their optical properties are investigated and compared qualitatively and quantitatively. Type A ceramic exhibits transmittance characteristics with very low internal loss in the visible to infrared wavelength region, while type B ceramic is inferior in various optical performances especially in the short (visible) wavelength region. In type B ceramic, birefringence occurs due to optical inhomogeneity in the visible region, resulting in a decrease in the extinction ratio. Non-uniform refractive index distribution is also observed in the Schlieren image of type B ceramic, hence the laser beam quality through that material is degraded. This study proved the importance of optical homogeneity of transparent ceramics and clarified the problems in actual applications.

Production of nanoporous silicate matrices—problems of optical homogeneity

Subject of study. This paper discusses the main stages of the fabrication of porous silicate matrices composed of two-phase borosilicate glass and how they affect the optical quality of the fabricated samples, as well as how to quantitatively characterize the optical inhomogeneity of the porous matrices, caused by nonuniformity of the pore distribution over the volume of the sample. How the geometry of the chemical processing of the samples is associated with their optical quality is also studied. Method. Digital holographic interferometry implemented on a laboratory-fabrication test stand is used to monitor the optical homogeneity. A technique is worked out to obtain interferograms that characterize the state of the sample in the form of a plane-parallel plate at the preform stage and after acid and alkali processing, as well as a technique for analyzing the experimental data. The quantitative results obtained at the early fabrication stages of the matrices were compared on the same section of the sample (to within 0.1 mm). The spectral transmission of the samples was measured in the 350–100-nm region. The free volume of the sample occupied by pores was determined by weighing, using the mass of the sample in the air-dried state and with the pores filled with water. Main results. A technique was developed for monitoring the optical quality of nanoporous silicate matrices, using a laboratory test stand for digital holographic interferometry. The optical homogeneity of a porous sample was monitored by diagnosing the relative variations of the sample’s optical thickness (the product of the refractive index times the sample’s geometrical thickness). These variations in the blank occur because the sides of the sample are not parallel. They are caused in a porous matrix both by the nonparallelness of the sides of the blank and by the inhomogeneity of the spatial variations of the refractive index due to inhomogeneous distribution of the pores in the volume of the sample. Based on this, quantities are introduced that characterize the optical quality of the blank and of the porous matrix. The optical quality of a plane-parallel blank was determined in this paper from a sample with nonparallel sides, while the optical quality of the nanoporous structure was determined from the refractive-index variation on a given section. It is shown that the orientation of a sample relative to the direction of the gravitational field during chemical processing significantly affects its optical quality. It is experimentally established that, when plane-parallel samples are oriented perpendicular to the gravitational field during chemical processing, it is possible to guarantee the optical quality of the porous matrices in the region where they are transparent, compared with the optical quality of the blank. Practical significance. A technique is presented that makes it possible to quantitatively characterize the optical inhomogeneity on a given section of a porous sample in the region where it is transparent and to separate the amount by which the quality of the blank and the optical inhomogeneity of the porous structure contribute to the optical quality of the fabricated nanoporous matrices. Our experiments showed that nanoporous silicate matrices that are transparent in the visible and near-IR regions and that are horizontally oriented during chemical processing possess optical homogeneity comparable with the optical quality of the blank. The technique for monitoring the quality of the samples can be used when developing and optimizing regimes for obtaining nanoporous matrices from two-phase glasses, intended for creating optical elements based on them that meet specifications in optical homogeneity.