Diffuse Reflection Coefficient Research Articles

Study of self-calibrating photodiodes for trap detectors

In accordance with the stated purpose of the study, the measurements and analysis of photodiodes were carried out, and the best alternative for the development of the trap detector was chosen. The paper substantiates the necessity for an alternative to the absolute cryogenic radiometer because of its highly expensive measurements. The need for more accurate measurement data has determined the use of trap detectors, including self-calibrating photodiodes. Such trap detectors can be used independently, without calibration by an absolute cryogenic radiometer. Thus, the cost of the study is reduced. Besides, the given approach does not affect the accuracy of the obtained measurement results.
 When reviewing modern approaches to the use of the above-mentioned trap detectors, it was discovered that trap detectors, together with self-calibrating photodiodes, are widely used both in state measurements of photometric quantities and for laboratory needs in many developed countries worldwide. The given analysis allows us to assert that the issues of developing, studying, and using new trap detectors, considering a significant advantage in their characteristics in comparison with the previously developed ones, make up an urgent scientific task.
 The paper defines selection criteria based on certain characteristics of photodiodes. When investigating the operating spectral range of the selected photodiodes, their internal quantum efficiency, geometrical dimensions of the receiving element of the selected photodiodes, and the coefficient of mirror and diffuse reflection of the receiving surface of the selected photodiodes, measurement results for all the stated characteristics were obtained. Based on these values, a screening of the photodiodes that do not meet the requirements for photodiodes specified for the development of the trap detector was made. Based on experimental studies, photodiodes S1337-1010BQ were selected.

Possibilities of Diffuse Reflectance Spectroscopy in Determining and Operational Control of the Optical Properties of Finely Dispersed Scattering Media

The characteristics of modern portable spectrometers based on photodetector arrays make it possible to create on their basis a new class of devices for operational control of the optical properties of various media. The introduction into the practice of diffuse reflectance spectroscopy with spatial resolution is hampered by the lack of an analysis of the influence of the width of the spectral region used and other sources of measurement uncertainty on the unambiguous determination of the optical properties of finely dispersed scattering materials. This article describes a method of determining the coefficient of local diffuse reflection and calculating the spectral parameters of the reduced scattering and absorption of radiation based on the differences in their shape, which are clearly manifested in a wide range of the spectrum. This allows the reduction in the determination of the desired spectral dependencies to the formation of a residual function that requires varying the values of only two parameters. A method for normalising the recorded spectral dependencies is described, which makes it possible to minimise the influence of the spectral characteristics of the equipment used on the recorded spectral–spatial profiles. Approbation of the method was carried out on examples of processing spectral–spatial diffuse reflection profiles of four samples of finely dispersed scattering structural materials, as well as diffuse reflection profiles of living tissue in the palm thenar region. The sources of uncertainty that affect the uniqueness of the obtained solutions are found, and solutions are proposed to minimise their influence on the desired spectral dependencies. The results obtained indicate the prospects of using the described method for creating equipment for non-destructive control of the optical properties of finely dispersed materials and media, including living tissues and food products.

Diffusion of light in turbid media with internal reflections

We relate the the Kubelka-Munk equations for the description of the intensity transfer of light in turbid media to a one-dimensional diffusion equation, which is obtained by averaging the three-dimensional diffusion equation over the lateral directions. This enables us to identify uniquely the Kubelka-Munk parameters and derive expressions for diffuse reflection and transmission coefficients including the effect of internal reflections. Without internal reflections we recover the Kubelka-Munk formulae for these coefficients. We show that the Kubelka-Munk equations are the proper radiative-transfer equations for the one-dimensional diffusion problem.

Driver's visual luminance model considering the reflection characteristics of a tunnel’s inner wall: Theory and practice I

A driver's visual luminance value under one-time stopping sight distance is the basic value for highway tunnel lighting design and quality evaluation. Currently, the driver's visual luminance value is obtained using the pavement reflection coefficient method with or without considering the diffuse reflection coefficient of the sidewall. This does not fully consider the influence of the reflection characteristics of the tunnel’s sidewall and pavement materials, potentially resulting in a large discrepancy between the measured and theoretically calculated values of driver’s visual luminance, which significantly affects the lighting design and quality evaluation of highway tunnels. Therefore, this study first establishes a driver's visual luminance theoretical model considering the reflection characteristics of the tunnel sidewall and pavement and uses the five-parameter model to fit the measured eigenvalues of the tunnel sidewall and pavement reflection to obtain a bidirectional reflectance distribution function. Theoretical calculation and actual measurement verification are performed using a 1:10 tunnel simulation model. Finally, the theoretically calculated value of visual luminance and the calculated values of the JTG and IESNA specifications are compared with the measured data of the tunnel simulation model. The results show that the mean error between the theoretically calculated value of visual luminance and the measured data remains at 6.0%, which is significantly lower than the corresponding errors in the JTG and IESNA specifications. After calculation, when a high diffuse reflection coating is applied to the sidewall of the tunnel, the driver's visual luminance can be increased by 16.8% on average.

Symmetrization and Amplification of Germicidal Radiation Flux Produced by a Mercury Amalgam UV Lamp in Cylindrical Cavity with Diffusely Reflective Walls

The study focused on increasing the efficiency of germicidal UV radiation by using highly diffuse reflective materials such as PTFE in irradiated cavities of UV air purifiers. In a conventional cylindrically symmetric cavity with a linear amalgam mercury lamp as UV-radiation source on the axis UV-radiation, flux directed from the lamp to the walls dropped from the axis to the periphery. To increase the UV irradiation, the walls are often made mirror-reflective, but the radiation flux distribution remained radially symmetric with a maximum on the source emitting surface in this case as well. When most of the emitted light is returned to the source after one reflection, the conditions of its operation are disturbed. If the walls are made of highly diffuse reflective materials, the radiation flux density inside the cavity increases on average, and its distribution becomes uniform and highly symmetric. Thus, the effect of amplification of the radiation flux due to the highly diffuse reflectivity of the walls increases with radius and reaches a maximum at the wall. Experiments were performed to demonstrate increasing amplification of germicidal UV radiation flux with a diffuse reflection coefficient in cylindrical cavities with walls of PTFE and ePTFE. The irradiation of the cavity wall was observed to increase up to 20 times at the resonant mercury line of 253.7 nm and up to 40 times at some non-resonant lines of the visible range due to highly diffuse reflectivity of the cavity walls. The flux amplification effect was limited by the diffuse reflectivity value of the walls and absorption coefficient of the radiation emitting surface. A formula for calculating the radiation flux amplification factor in a diffusely reflecting cylindrically symmetric cavity was derived for the case of Lambertian source and reflector, including wall reflectivity and source surface absorption coefficients. The effects of heating and cooling of the mercury lamp amalgam directly affected the amplification, and symmetrization of germicidal irradiation was observed and is discussed in the paper. Numerical calculations were performed by the ray tracing method. The calculated model was verified by comparing the numerical results with those of both the approximate theoretical consideration and experiments. The promising use of diffusely reflecting cylindrical cavities for UV air purifiers is discussed. Designs of air inlet and outlet ports that allow effective locking of germicidal radiation inside the UV air purifiers were considered. The results of this work may be of interest for further developments in the UV disinfection technique.

Comparative analysis of optical properties of coals by petrography and spectroscopy methods

This paper reports determining the grayscale intensity of macerals in the coal lump polished sections oriented along and across the layering of three main groups of sub-bituminous, high volatile bituminous, low volatile bituminous coals. All measurements have been performed in white, red, yellow, green, blue light. The influence of all selected factors and most of their combinations on grayscale intensity is reliable; the most pronounced effects are established for the optical filter color and the maceral type. Comparative analysis of the grayscale intensity data array with the spectra of full reflectance in the visible region and the coefficient of diffuse reflection in the white light of fine powders of the same samples has been carried out. Green light yields a very dark image of vitrinite and liptinite with the grayscale intensity approaching zero. In two of the six samples, the reflectance level of inertinite in yellow light is significantly higher than the grayscale intensity of white light. This anomaly is associated with a hypsochromic shift in the inertinite maximum absorption. The approach used is an alternative method for quantifying the relative changes in reflectivity and position of the diffuse spectral minimum without applying a microspectrometer.

Study on the effect of low-temperature atmospheric pressure plasma jet on the morphofunctional properties of living tissues (in vivo)

The results of spectral-fluorescent and diffuse-optical studies of living tissues under the effect of low-temperature atmospheric pressure plasma jet in a mixture of air and argon are presented. Potential fluorophores are identified and coefficients of optical absorption and transport scattering of tissues are determined. It was revealed plasma jet irradiation of tissue leads to an increase in the intensity of fluorescence and the diffuse reflection coefficient, which is linked with a twofold increase in the transport scattering coefficient and a change in the concentration of endogenous chromophores --- a reducing water content, lipids and bilirubin to 20%, and an increasing levels of oxygen saturation to 10%. On the basis of the analysis, it is shown that the therapeutic effect of low-temperature plasma can be associated with increased antioxidant protection and the development of compensatory dehydration processes. Keywords: biological tissues, cold plasma, probing, spectroscopy, fluorescence, diffuse reflection, optical coefficients, light scattering, biochemistry, morphology.

Исследование морфофункциональных свойств биотканей ( in vivo) при воздействии низкотемпературной плазменной струи атмосферного давления

The results of spectral-fluorescent and diffuse-optical studies of living tissues under the effect of low-temperature atmospheric pressure plasma jet in a mixture of air and argon are presented. Potential fluorophores are identified and coefficients of optical absorption and transport scattering of tissues are determined. It was revealed plasma jet irradiation of tissue leads to an increase in the intensity of fluorescence and the diffuse reflection coefficient, which is linked with a twofold increase in the transport scattering coefficient and a change in the concentration of endogenous chromophores – a reducing water content, lipids and bilirubin to 20%, and an increasing levels of oxygen saturation to 10%. On the basis of the analysis, it is shown that the therapeutic effect of low-temperature plasma can be associated with increased antioxidant protection and the development of compensatory dehydration processes.

Detection of Ultralow Light Power Back-Reflected or Back-Scattered by Optical Components Using Balanced Low-Coherence Interferometry

We use balanced optical low-coherence interferometry to measure the ultralow light power back-reflected and/or back-scattered by optical interfaces. Indeed, backscattered light from optical surfaces can be a critical source of noise in interferometric gravitational-wave detectors, such as the Laser Interferometer Gravitational-Wave Observatory (LIGO), Virgo, or the Laser Interferometer Space Antenna (LISA), and therefore, it is required to characterize, with high sensitivity, the scattering properties of elementary components involved in their optical design. The use of a broadband light source makes an easy identification of the scattering interface possible, while the implementation of balanced interferometric detection allows very low light levels to be detected, thanks to the simultaneous use of coherent gain and source intensity noise suppression. Experimental results are reported, first on bare glass optical windows (N-BK7 and S-LAH66) and then on a silver-coated mirror, that demonstrate the ability of this setup to quantify specular- or diffuse-reflectance coefficients as low as ${10}^{\ensuremath{-}11}$.

White vitreous enamel for ferrous metals with preliminary thermal activation of frit

Vitreous enamels represent a class of inorganic coatings with different properties. In this article, a white vitreous enamel of the Na2O–B2O3–TiO2–SiO2 system for enameling of cast iron is introduced. In contrast to the enamel for other metals, the enamel for cast iron must exhibit a high spreading and coefficient of thermal expansion (CTE) of 40–70 mm and 110–120·10−7 1/K, respectively. The objective was to obtain an enamel with high whiteness (coefficient of diffuse reflection, CDR not less 80%) and chemical resistance not lower than class A+. This enamel was obtained by correcting the basic composition of the enamel and changing the ratio of SiO2/B2O3 and Na2O/K2O oxides. The formulation of the frit contained oxides in the following quantities in wt.%: SiO2, 43; B2O3, 12; P2O5, 4; TiO2, 15; Al2O3, 2; MgO, 2; Na2O, 12; K2O, 6; and ZnO, 4. This enamel exhibited a set of specified properties. At a temperature of 850 °C, the spreading of enamel was 53 mm, CTE was 110·10−7 1/K, and chemical resistance was of class A+. The whiteness property (CDR 83%) was achieved only using an additional technological operation, i.e., the thermal activation of the frit. The thermal activation of the frit at 500 °C for 30 min induced the formation of a fine-crystalline homogeneous coating structure and TiO2 in the form of anatase. Thermal activation shifts the crystallization temperature to the field of lower temperatures, this is confirmed by the data of the differential thermal analyses. Electron microscopy findings indicated differences in the structure of the enamel after etching in hydrofluoric acid obtained from the frit with and without thermal activation. Preliminary thermal activation of the frit helps obtain a uniform fine-crystalline structure of the coating.

Analysis and Radiometric Calibration for Backscatter Intensity of Hyperspectral LiDAR Caused by Incident Angle Effect.

Hyperspectral LiDAR (HSL) is a new remote sensing detection method with high spatial and spectral information detection ability. In the process of laser scanning, the laser echo intensity is affected by many factors. Therefore, it is necessary to calibrate the backscatter intensity data of HSL. Laser incidence angle is one of the important factors that affect the backscatter intensity of the target. This paper studied the radiometric calibration method of incidence angle effect for HSL. The reflectance of natural surfaces can be simulated as a combination of specular reflection and diffuse reflection. The linear combination of the Lambertian model and Beckmann model provides a comprehensive theory that can be applied to various surface conditions, from glossy to rough surfaces. Therefore, an adaptive threshold radiometric calibration method (Lambertian–Beckmann model) is proposed to solve the problem caused by the incident angle effect. The relationship between backscatter intensity and incident angle of HSL is studied by combining theory with experiments, and the model successfully quantifies the difference between diffuse and specular reflectance coefficients. Compared with the Lambertian model, the proposed model has higher calibration accuracy, and the average improvement rate to the samples in this study was 22.67%. Compared with the results before calibration with the incidence angle of less than 70°, the average improvement rate of the Lambertian–Beckmann model was 62.26%. Moreover, we also found that the green leaves have an obvious specular reflection effect near 650–720 nm, which might be related to the inner microstructure of chlorophyll. The Lambertian–Beckmann model was more helpful to the calibration of leaves in the visible wavelength range. This is a meaningful and a breakthrough exploration for HSL.

Simulation Experiment on Tunnel Lighting Aided by High Diffuse Reflectance Materials

The existing tunnel lighting calculation methods only consider the effect caused by direct light source and ignores the reflection effect of light flux emitted by lamps inside the tunnel closed pipe, which is not conducive to the energy saving and safety of tunnel lighting.In this paper, a tunnel illumination calculation method considering the reflection increment of tunnel sidewall is proposed. This method is based on the diffuse reflection coefficient of tunnel sidewall material which can characterize the reflection characteristic of its surface, so as to calculate the illuminance of road surface.Matlab software was used to simulate the real lighting environment of the tunnel with energy storage luminescent material as the side wall. It was found that the increase of reflection caused by high-quality tunnel interior materials could effectively improve the tunnel lighting

Исследование массива вертикально-ориентированных многостенных углеродных нанотрубок для абсолютно черного тела

An array of vertically oriented multi-walled carbon nanotubes (VOMWCNT), obtained by chemical vapor deposition (CVD) on a silicon substrate without preliminary catalyst deposition, has been comprehensively investigated. The synthesis was carried out for 30 minutes in the reactor of a carbon nanotube synthesis unit under conditions of decomposition of the reaction mixture (ferrocene in heptane) at a temperature of 800 °C at a carrier gas flow rate of 200 ml/min. The structure and geometric characteristics of the array’s carbon nanotubes were determined using scanning and transmission electron microscopy and Raman spectroscopy. The spectral coefficient of diffuse reflection (SDR) into the hemisphere in the wavelength range from 5,0 to 15,0 μm was determined. From the obtained experimental data, it was found that the emissivity (absorption coefficient) of an array of carbon nanotubes with a height of (230 – 250) μm is 0,98 – 0,99 in the spectral range from 5,0 to 13,7 μm and 0,975 – 0,995 in the range from 13,7 to 15,0 μm. Such a VOMWCNT array can be used to develop an absolutely black body with a high absorption coefficient and small mass and size characteristics, which is used for calibrating spacecraft’s infrared spectrometers.

Influence of Different Structure and Specification Parameters on the Propagation Characteristics of Optical Signals Generated by GIL Partial Discharge

Partial discharge (PD) leads to the generation of electrical, acoustic, optical, and thermal signals. The propagation characteristics of optical signals in gas insulated metal-enclosed transmission lines (GIL) are the basis of optical detection research. This paper simulates the propagation of PD optical signals in GIL through modeling GIL with different structures and specification parameters. By analyzing the optical parameters on the probe surface and the detection points when the PD source position is different, the influence of the difference in specifications caused by the voltage level on the propagation of the GIL PD optical signal is studied. The results show that the GIL cavity structure will affect the faculae distribution and the relative irradiance (RI) of the detection surface; the PD source position has a huge impact on the faculae distribution on the detection surface, but has little influence on the RI; as the voltage rises, the faculae distribution on the detection surface becomes more obvious, and the mean of RI decreases. The above results have the reference value for the manufacture of GIL equipment and the research of PD optical detection. When the specular reflection coefficient of surface material is smaller and the diffuse reflection coefficient is larger, the outline of the light spot is clearer, the proportion of brighter parts is larger, and the maximum value of the RI is larger.

Determination of Diethyldithiocarbamate in the Solid Phase of a Fibrous Cation Exchanger in the Cu-Form Using Diffuse Reflectance Spectroscopy

Diffuse reflectance spectroscopy was used to study the interaction of sodium diethyldithiocarbamate (DEDTC) with copper ions adsorbed on the disks of a PANF–KU-2 fibrous cation exchanger. The conditions for obtaining the substrate in the Cu-form are determined. The dependence of the analytical signal on the adsorption conditions of DEDTC was studied: the pH of the solution, the contact time of the solution with the substrate, the volume of the solution, and the concentration of DEDTC in the solution. Diffuse reflectance spectra of the PANF–KU-2–Cu substrate and the complex of DEDTC with Cu in the PANF–KU-2 phase were recorded. The best analytical signal was observed at 450 nm. A probability of the formation of Cu(DEDTC) and Cu(DEDTC)2 complexes on the adsorbent surface depending on the concentration of DEDTC in the solution was noted. The PANF–KU-2–Cu substrate can be used for the adsorption and determination of 0.1–0.6 µg/mL of DEDTC in alkaline solutions (pH 7–10) by measuring the diffuse reflectance coefficient of disks at 450 nm. The procedure was tested on model solutions of tap water.

Comparison of some Methods for Noninvasive Diagnostics of Human Skin Parameters by Scattered Light

The possibility of determining the structural and biophysical parameters of skin from the spectra of scattered light is assessed. Schemes for measurement of the coefficient of diffuse reflection, the coefficient of brightness back-scattered by biological tissue, and the spatial illumination at some distance from the source are examined. Algorithms are proposed for establishing the volume concentrations of melanine and blood vessels, the thickness of the epidermis, the degree of oxygenation of the blood, and the average diameter of the capillaries. It is shown that the first two schemes give approximately identical characteristics for solution of the inverse problem, although the polarization measurements are somewhat less susceptible to experimental error. Analysis of such similarity has demonstrated that it is due to features of the optical characteristics of the skin layers. The preferred method is the third experimental scheme, which is not subject of error and has substantially higher sensitivity to the degree of oxygenation of the blood and the average diameter of the capillaries and makes it possible to establish all the desired parameters of the skin with acceptable accuracy for practical purposes.

Performance of Textured Metallized Teflon Coverings with High Diffuse Reflectance Coefficient in Low Earth Orbit on ISS

The data of mathematical modeling of the thermal state of a cutting tool under conditions of laser hardening are presented. The features of the implementation of the method of polyargument systems for solving the three-dimensional heat transfer problem with a localized movable laser heating source are considered. The data of numerical studies to establish patterns of the influence of the radius of the heating spot on the temperature regime of the hardened tool are presented. It is shown that varying this parameter can be used as an effective way of influencing the thermal state of a cutting tool during its hardening by a laser beam. The results of modeling the temperature conditions of the tool in a wide practically important range of changes in its sharpening angle are presented.

“Smart” anti­corrosion pigment based on layered double hydroxide: construction and characterization

Paint coatings are widely used for decorative purposes and to prevent corrosion of metal surfaces. However, regular paint coating only provides passive protection of the metal. To create an active type of corrosion protection, various anti-corrosion additives are added to paint formulations. As a result of analyzing available data, a bi-functional (colored and anti-corrosion) pigment was theoretically constructed as monophase Zn-Al-tripolyphosphate LDH with the generalized formula Zn 0.8 Al 0.2 (P 3 O 10 ) 0.04 . In this LDH, Zn 2+ as “host” cation and Al 3+ as “guest” cation govern white color of the pigment, and intercalated tripolyphosphate-anions – corrosion inhibitor. A continuous constant pH synthesis at a temperature of 70°С was selected as a preparation method. This method was used to prepare theoretically constructed pigment. The crystal structure of the pigment sample was studied by means of X-ray diffraction, morphology and particle size were determined by means of scanning electron microscopy, thermal properties were evaluated by means of thermogravimetry. Color characteristics were recorded using the color comparator, anti-corrosion properties were evaluated by recording anodic polarization curves of 08KP steel in 5 % (wt.) Na 2 SO 4 solution with and without the pigment extract. By means of X-ray diffraction analysis, it was found that bi-phase precipitate, containing the constructed LDH (with Zn(OH) 2 structure) and Zn-Al LDO (ZnO structure) was formed. This indicated partial decomposition of LDH during synthesis, but the reason for it is unknown. By means of SEM, the formation of agglomerates of the same particles with high surface area was found. The study of color characteristics revealed that the prepared pigment has high whiteness value (diffuse reflection coefficient above 90 %, color purity below 1 %, lightness above 96 %). This is due to the color of both LDH and LDO phases. By recording anodic polarization curves, it was found that corrosion rate in the presence of water extract of the pigment is lower by 5.36 times (corrosion current density decreased from 5.63 mA/cm 2 to 1.03 mA/cm 2 . All of this shows that a bi-functional pigment was prepared, which has great pigment properties, high whiteness, and high anti-corrosion properties.

Determination of Copper(II) Ions by Diffuse Reflectance Spectroscopy Method

A method for copper(II) determination based on copper(II) ions interaction with the organic reagent picramine-ε, concentrating the formed complex on a solid-phase matrix and recording diffuse reflectance spectroscopy spectra by a portable combined LED miniphotometer was developed. Poly-ε-caproamide membranes were investigated as solid-phase matrixes. It was found that the diffuse reflectance coefficient of the studied membranes in the visible spectrum region does not depend on wavelength. So, the signal from membranes does not distort the results of the analysis. Factors controlling the process of sorption of the copper(II) complex with picramine-ε were studied. It was shown that the poly-ε-caproamide membranes are effective sorbents which provide the possibility of concentrating the analyte at a level higher than 105. The dependences of analytical signal on the acidity of the solution, the time of keeping the complex in the solution and the initial volume of the solution passed through the membrane were studied. Based on the obtained data, the optimal conditions of the analysis were found. Calibration dependence of the analytical signal on the concentration of copper(II) in model solutions was estimated. The method was tested for the determination of copper(II) ions in white wine. The method of additives was used for the analysis. It was found that the concentration of copper(II) ions in “Vagrus” wine is 0.0016 mkg/ml.

A Global Optimization Method for Specular Highlight Removal From a Single Image

The presence of specular highlight is a critical issue for both natural and medical images such as those produced by laparoscopes, which can lead to erroneous visual tracking, stereo reconstruction, and image segmentation. Specular highlight removal from a single image is necessary for image analysis and applications. Due to the differences between natural and medical image scenes, existing literature to address this issue has only been effective on natural images or medical images with textureless regions. To overcome this limitation, we propose a global optimization method for specular highlight removal from a single image based on a dichromatic reflection model. In addition to introducing modified illumination chromaticity, the proposed method consists of two novel steps: one for estimating diffuse chromaticity by correcting hue and saturation on highlighted regions, and the other for estimating diffuse and specular reflection coefficients using convex optimization with double regularization. The estimated diffuse chromaticity is proven to approximate the true diffuse chromaticity and the proposed optimization algorithm is guaranteed to find the optimal diffuse coefficients. Experimental results show that the proposed method can effectively remove specular highlights from both natural images and endoscopic images with texture detail preservation. To further demonstrate the efficacy of our proposed method, an application of stereo reconstruction using a public dataset illustrates that our highlight removal method can enhance surface reconstruction accuracy from 1.10mm RMSD to 0.69mm RMSD.