Specular Reflection Coefficient Research Articles

Formation of Tubular Aluminum Oxides by Local Electrochemical Anodization in Organic Electrolytes and Their Anti-Reflection Properties

Research has been carried out on the formation of tubular aluminum oxides by local electrochemical anodization in aqueous solutions of organic acids such as formic, citric, tartaric, malic and others. Self-ordered nanostructures formed this way can be used in the manufacture of various optical devices. Tubular aluminum oxides formed by local electrochemical anodization in organic acids have a high concentration of anionic complexes containing carbon atoms over 10 at.%. Studies of reflection spectra showed effective anti-reflection properties of films with a specular reflection coefficient of 0.7–1.4 %.

Utilizing non-specular reflection of bounded ultrasonic beams for assessing damage in solid plates

This paper investigates the potential of utilizing non-specular reflection of a bounded ultrasonic beam in a liquid-solid-liquid structure as a method for assessing damage in solid plates. The study focuses on understanding the acoustic field formulation resulting from this type of reflection, as well as examining the impact of incident angles and material damage (indicated by reduced Young's modulus) on the non-specular reflection field. To quantify the effects of non-specular reflections, the specular reflection coefficient (SRC) proposed by the authors is employed (Wang and Deng, 2023) [1]. A finite-element (FE) model is developed to analyze the SRC response concerning the incident angle and material damage. Through FE simulations involving obliquely incident bounded ultrasonic beams at different angles, the research reveals a significant, monotonically increasing sensitivity of the SRC change rate at the S0 critical angle to the level of material damage. This finding offers a precise approach for accurately evaluating material damage in plates. Experimental tests are conducted on a water-aluminum sheet-water structure, which validates the theoretical predictions and FE simulation results. The experimental results consistently demonstrate an increased change rate of the SRC at the S0 critical angle in response to the fatigue cycle, confirming the effectiveness of using non-specular reflection of a bounded ultrasonic beam at the S0 critical angle as a method for evaluating material damage in plates.

Evaluation of material damage using non-specular reflection of a bounded ultrasonic beam at a liquid-solid interface

This paper proposes an effective method for evaluating the level of material damage using the non-specular reflection of a bounded ultrasonic beam at a liquid-solid interface. Non-specular reflection occurs when a bounded ultrasonic beam is obliquely incident from a liquid onto a solid surface. This paper formally formulates the acoustic field of the non-specular reflection of a bounded ultrasonic beam and analyzes the influences of some factors such as the incident angle and the level of material damage (characterized by a decrease in Young's modulus) on the non-specular reflection field. To characterize the effect of the non-specular reflection of a bounded ultrasonic beam, this paper defines a specific parameter called the specular reflection coefficient (SRC) of a bounded ultrasonic beam. A finite-element (FE) model is established to quantitatively observe the response of the defined SRC to the incident angle and the level of material damage. The FE simulations are conducted for the bounded ultrasonic beam obliquely incident at longitudinal, transverse, and Rayleigh critical angles, respectively. The simulations demonstrate that the change rate of SRC at the Rayleigh critical angle exhibits a monotonically sensitive response to the level of material damage, providing an effective means for accurately evaluating it. To validate this method, we conducted an experiment with oblique incidence testing of the bounded ultrasonic beam at the Rayleigh critical angle of the water-aluminum interface. The experimental results are consistent with the FE simulations, and show that the change rate of SRC at the Rayleigh critical angle has a monotonous and sensitive response to the level of material damage. The consistency of theoretical predictions, FE simulations, and experimental results confirms the feasibility of using the non-specular reflection of a bounded ultrasonic beam incident at the Rayleigh critical angle as an effective method for evaluating the level of material damage.

Toward very large baseline interferometry observations of black hole structure

Black holes hold a tremendous discovery potential. In this paper the extent to which the Event Horizon Telescope and its next generation upgrade can resolve their structure is quantified. Black holes are characterized by a perfectly absorptive boundary, with a specific area determined by intrinsic parameters of the black hole. We use a general parametrization of spherically symmetric spacetimes describing deviations from this behavior, with parameters controlling the size of the central object and its interaction with light, in particular through a specular reflection coefficient $\Gamma$ and an intrinsic luminosity measured as a fraction $\eta$ of that of the accretion disc. This enables us to study exotic compact objects and compare them with black holes in a model-independent manner. We determine the image features associated with the existence of a surface in the presence of a geometrically thin and optically thick accretion disc, identifying requirements for VLBI observations to be able to cast meaningful constraints on these parameters, in particular regarding angular resolution and image dynamic range. For face-on observations, constraints of order $\eta\lesssim 10^{-4}, \Gamma\lesssim 10^{-1}$ are possible with an enhanced EHT array, imposing strong constraints on the nature of the central object.

Temperature dependencies of the refractive index for Al-Ga-In-As metamorphic layers.

Temperature dependencies of the refractive indices, n, for InxGa1-xAs and InxAl1-xAs metamorphic layers with x=0.06-0.25 have been determined. For this purpose, we performed variable-temperature (80 to 400 K) measurements of the specular reflection coefficient using custom distributed-Bragg-reflector structures in the spectral range from 0.8 µm to 2.2 µm. All the compositions exhibited a nearly linear temperature dependence of n. For InxGa1-xAs, the temperature coefficient (dn/dT) increases from 2.0⋅10-4K-1 for x=0.06 to 4.5⋅10-4K-1 at x=0.25. In turn, the temperature coefficient of the InxAl1-xAs refractive index stays at the level of (1.7-2.0)⋅10-4K-1 at the considered indium contents.

Procedural Measurement Error in Specular Reflection Coefficient from Planar Samples Using Two Different Types of Test Stands

Procedural Measurement Error in Specular Reflection Coefficient from Planar Samples Using Two Different Types of Test Stands

Specular reflection of hard gamma-quanta from surfaces with different roughness

A model on the structure of a thin, weakly diverging beam of hard electron bremsstrahlung and its transformation during its reflection from a microscopically smooth surface at small angles had been developed, which makes it possible to establish dependences of the specular reflection coefficients on the angular and energy distributions. Experimentally, the reflection of a bremsstrahlung beam with the boundary energy Ee = 6.25 MeV formed at a sliding angle α = 40 μrad with an angular divergence δγ = 27 μrad from the surface of mercury (surfaces with various roughness) was investigated on a 120-meter base. The dependences of the specular reflection coefficients on the sliding angles, the energy of the reflected γ-radiation, and the surface roughness found in this experiment correspond to theoretical predictions.

Methodical errors in measuring the specular reflection coefficient from a planar sample of material for two types of measuring facilities

This paper is discussed two methods for measuring the bistatic scattering characteristics of flat samples of the material. The experimental studies and numerical simulations of the dependence of the specular reflection coefficient on the incident angle of wave on a flat material sample carried out in the bistatic scheme of the experiment (rotation of the receiving and transmitting antennas) and in the monostatic scheme using a dihedral corner reflector (rotation of the object). Measurements for the magnetodielectric flat sample were carried out in ITAE RAS on two test facilities with the corresponding scheme of the experiment. To identify the errors of the methods used, we carried out numerical simulations of the measurement of the specular reflection coefficient of the sample under test by the method of integral equations (method of moments) in the FEKO program in the formulation of two experimental schemes. The obtained results were compared with each other and with the results of analytical calculations of the specular reflection coefficient carried out using the Fresnel formulas when considering an infinite flat layer of material. These calculations make it possible to compare the methodical errors in measuring the reflection coefficient in the two considered experimental schemes. It was shown that the results of the measurements using the corner reflector give methodical errors (deviations from the analytical calculation) by 1–2 dB more than the measurements on the bistatic facility. The results of experiments and numerical simulations are in agreement with each other. The conclusions obtained in this work are applicable to any experimental facilities for the study of planar materials.

The role of electrical conductivity in radar wave reflection from glacier beds

Abstract. We have examined a general expression giving the specular reflection coefficient for a radar wave approaching a reflecting interface with normal incidence. The reflecting interface separates two homogeneous isotropic media, the properties of which are fully described by three scalar quantities: dielectric permittivity, magnetic permeability, and electrical conductivity. The derived relationship indicates that electrical conductivity should not be neglected a priori in glaciological investigations of subglacial materials and in ground-penetrating radar (GPR) studies of saturated sediments and bedrock, even at the high end of typical linear radar frequencies used in such investigations (e.g., 100–400 MHz). Our own experience in resistivity surveying in Antarctica, combined with a literature review, suggests that a wide range of geologic materials can have electrical conductivity that is high enough to significantly impact the value of radar reflectivity. Furthermore, we have given two examples of prior studies in which inclusion of electrical conductivity in calculation of the radar bed reflectivity may provide an explanation for results that may be considered surprising if the impact of electrical conductivity on radar reflection is neglected. The commonly made assumption that only dielectric permittivity of the two media needs to be considered in interpretation of radar reflectivity can lead to erroneous conclusions.

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.

Influence of antichiral edge states on Andreev reflection in graphene-superconductor junction

Using the tight binding model and the non-equilibrium Green function method, we study Andreev reflection in graphene-superconductor junction, where graphene has two nonequal Dirac Cones split in energy and therefore time reversal symmetry is broken. Due to the anti-chiral edge states of the current graphene model, an incident electron travelling along the edges makes distinct contribution to Andreev reflections. In a two-terminal device, because Andreev retro-reflection is not allowed for just the anti-chiral edges, in this case the mutual scattering between edge and bulk states is necessary, which leads that the coefficient of Andreev retro-reflection is always symmetrical about the incident energy. In a four-terminal junction, however, the edges are parallel to the interface of superconductor and graphene, so at the interface an incident electron travelling along the edges can be retro-reflected as a hole into bulk modes, or specularly reflected as a hole into anti-chiral edge states again. It is noted that, the coefficient of specular Andreev reflection keeps symmetric as to the incident energy of electron which is consistent with the reported results before, however the coefficient of Andreev retro-reflection shows an unexpected asymmetrical behavior due to the presence of anti-chiral edge states. Our results present some new ideas to study the anti-chiral edge modes and Andreev reflection for a graphene model with the broken time reversal symmetry.

Experimental Approbation of Reference Layer Method in Resonant Neutron Reflectometry

Abstract—The first application of resonant neutron scattering at Gd atoms for the experimental determination of the phase of the reflection coefficient in neutron reflectometry is presented in this paper. The surface of the sample studied was covered by the reference Gd layer, for which the scattering length of thermal neutrons is highly energy-dependent. After measuring the coefficient of specular reflection of neutrons at three different wavelengths of each impulse, we were able to resolve the phase problem of the neutron reflectometry and determine the absolute magnitude and phase of the complex reflection coefficient from an unknown part of sample structure.

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.

Calculating the High-Frequency Electrical Conductivity of a Thin Metallic Layer for an Ellipsoidal Fermi Surface

The conductivity of a thin metallic layer in an ac electric field is calculated with respect to different specular reflection coefficients of the layer surfaces for an ellipsoidal Fermi surface. The ratio between the free path of electron conduction and layer thickness is not limited. The dependences of the absolute value and the argument of dimensionless conductivity on the dimensionless layer’s thickness, dimensionless external electric field frequency, and specular reflection coefficient of one of the layer surfaces at different ellipticity parameters of the Fermi surface are analyzed.

Effect of Boundary Conditions on the Electrical and Galvanomagnetic Properties of a Thin Metal Film

The problem of determining the high-frequency electrical conductivity and Hall constant for a thin metal film placed in a transverse stationary magnetic field and in a longitudinal alternating electric field is solved by the kinetic method. The relation between the film thickness and electron free path length is supposed to be arbitrary. The skin effect is not taken into account. The diffuse-specular mechanism of electron reflection from the film boundaries is considered with similar specular-reflection coefficients for the upper and lower surfaces of the film taken into account. The electrical conductivity and Hall constant are studied as functions of dimensionless parameters: electric-field frequency, magnetic-field induction, and film thickness.

Calculating the high-frequency electrical conductivity of a thin semiconductor film for different specular reflection coefficients of its surface

In this paper, using the kinetic method, we calculate the conductivity of a thin semiconductor layer in an alternating electric field taking into account the different specular reflection coefficients of its surfaces. No constraints are imposed on the relation between the free path length of the electrons (holes) and the thickness of the layer. The dependences are analyzed of the modulus and the argument of the dimensionless conductivity on the dimensionless thickness of the layer, the dimensionless frequency of the external electric field, and specular reflection coefficient of one of its surfaces. The results are compared with the theoretical calculations and the experimental data for a metal film.

Electric current distribution in a thin metal layer for various specular reflection coefficients of its surfaces

The distribution of electric current in a thin metal layer has been calculated for various specular reflection coefficients of its surfaces. The dependence of the conductivity on the distance from the lower surface of the layer has been analyzed. The Boltzmann kinetic equation in the relaxation time approximation has been used.

Analysis of mirror soft-x-ray-EUV scattering using generalized continuous growth model of multiscale reliefs.

Combined computer simulations of the growth of multilayer mirrors and their exact differential reflection coefficients in the soft-x-ray-EUV range have been conducted. The proposed model describes the variation of the surface roughness of the multilayer Al/Zr mirror boundary profiles taking into account a random noise source. Theoretically calculated Al/Zr boundary profiles allow one to know real rough boundary statistics including rms roughnesses and correlation lengths and, to obtain rigorously EUV specular and diffuse reflection coefficients. The proposed integrated approach opens up a way to performing exact theoretical studies similar in accuracy to results obtained by quantitative microscopy investigations of nanoreliefs and synchrotron radiation measurements.

Reflection of a TE-polarised Gaussian beam from a layered structure under conditions of resonance excitation of waveguide modes

The problem of reflection of a TE-polarised Gaussian light beam from a layered structure under conditions of resonance excitation of waveguide modes using a total internal reflection prism is considered. Using the spectral approach we have derived the analytic expressions for the mode propagation lengths, widths and depths of -lines (sharp and narrow dips in the angular dependence of the specular reflection coefficient), depending on the structure parameters. It is shown that in the case of weak coupling, when the propagation lengths of the waveguide modes are mainly determined by the extinction coefficient in the film, the depth of -lines grows with the mode number . In the case of strong coupling, when is determined mainly by the radiation of modes into the prism, the depth of -lines decreases with increasing . The change in the TE-polarised Gaussian beam shape after its reflection from the layered structure is studied, which is determined by the energy transfer from the incident beam into waveguide modes that propagate along the structure by the distance , are radiated in the direction of specular reflection and interfere with a part of the beam reflected from the working face of the prism. It is shown that this interference can lead to the field intensity oscillations near -lines. The analysis of different methods for determining the parameters of thin-film structures is presented, including the measurement of mode angles and the reflected beam shape. The methods are based on simultaneous excitation of a few waveguide modes in the film with a strongly focused monochromatic Gaussian beam, the waist width of which is much smaller than the propagation length of the modes. As an example of using these methods, the refractive index and the thickness of silicon monoxide film on silica substrate at the wavelength are determined.

Determining appropriate ambient lighting levels in Radiology reporting rooms

Determining appropriate ambient lighting levels in Radiology reporting rooms