Refraction Angle Research Articles

Reflectivity of light on axisymmetric radiation receiver of cylindrical parabolic solar energy concentrator

This series of articles is dedicated to the development of general theoretical approach to definition of characteristic of cylindrical-parabolic solar energy concentrator with axisymmetric radiation receiver, making it possible to optimize its parameters and to improve its optical efficiency. In this article, characteristics of electromagnetic radiations reflected on the interface with semiconductor receiver–converters of radiations into other kinds of energy or with their protection coatings, have been studied related to the lows of geometrical optics for relationships for incidence, reflection and refraction angles. Reflectivity and reflected aggregate fluxes of direct (nonreflected from the specular concentrator) radiation from the surface of axisymmetric receiver depending on refraction index n of rays by radiation receiver have been defined. The values have been defined and the dependences have been studied for reflectivities from the surface of receiver of radiation flow incident on the specular surface, for various concentrator design structures, including the following configurations: the axis of radiation receiver coincides with the focus of specular surface, the focus of specular surface coincides with the lower generatrix of receiver and for various positions of the focus of specular surface inside the receiver, on its symmetry plane.

Broadband achromatic metalens and meta-deflector based on integrated metasurface

Metasurfaces have attracted much attention due to their great ability to manipulate the electromagnetic field over an ultra-compact profile, which facilities the realization of the next generation diffractive optical elements. However, the broadband performance of the metasurface-based optical devices is still subject to the chromatic aberration. Although the broadband achromatic metalenses have recently been studied, the diameters and numerical apertures of the metalens are still limited by the requirement of large phase compensation. Such large phase dispersion is usually realized by sophisticated nanostructures of extremely high aspect ratios that are not easy to fabricate. Here we propose a new kind of metalens by integrating the dielectric pillars with a multi-level phase plate, and achromatic focusing and imaging can be achieved in the wavelength range from 1100 to 1500 nm. In addition, a broadband achromatic meta-deflector is also proposed, which could refract broadband incident light with the same refractive angle. Our integrated metasurface can provide large phase compensation while alleviating the aspect ratios of the composing nanopillars, and shows potential applications in designing arbitrary metadevices with dispersion engineering properties.

Large Axis Difference Between Topographic Anterior Corneal Astigmatism and Manifest Refractive Astigmatism: Can Topography-Guided LASIK Target the Manifest Axis?

To investigate whether the degree of astigmatism axis discrepancy between preoperative manifest refractive astigmatism and anterior corneal astigmatism impacts refractive and visual outcomes of primary topography-guided laser in situ keratomileusis (LASIK) targeting the refractive astigmatism, and to provide guidance on treating eyes with very large axis discrepancy. Comparative retrospective analysis of 25,396 consecutive eyes treated with topography-guided LASIK on the manifest refractive astigmatism. Standard outcomes of the 14,534 eyes with small axis discrepancy (SAD) (Δ in axis ⩽ 10°) were compared to the 2,222 eyes with very large axis discrepancy (VLAD) (Δ in axis ⩾ 45°). Pearson correlation coefficient was used to assess relationships between selected variables. The mean axis discrepancy was 4.47 ± 2.92° in SAD eyes, and 65.0 ± 13.4° in VLAD eyes. An equivalent number of eyes achieved a cumulative postoperative unilateral uncorrected distance visual acuity of 20/20 in both the SAD and VLAD groups (93.02% vs 93.42%; P = .4892). The efficacy index (0.98 ± 0.13 vs 0.98 ± 0.07; P = .3931) and the safety index (1.00 ± 0.11 vs 1.00 ± 0.03; P = .4757) were identical between groups. There was no clinically meaningful correlation between the preoperative axis discrepancy and preoperative total root mean square anterior corneal coma, postoperative refractive astigmatism, defocus equivalent, spherical equivalent, and angle of error, all with weak correlation coefficients (R = -0.02, -0.03, -0.02, 0.01, and 0.05). Large preoperative axis discrepancy (45° to 90°) between refractive astigmatism and topography-measured anterior corneal astigmatism does not negatively impact topography-guided LASIK, having identical refractive and visual outcomes compared to eyes with small (0° to 10°) discrepancy. There is no basis to exclude eyes with large axis discrepancy from topography-guided LASIK, and these eyes should be treated on the manifest refractive astigmatism. [J Refract Surg. 2021;37(10):662-673.].

Improved microscopy with ultraviolet surface excitation (MUSE) using high-index immersion illumination.

Microscopy with ultraviolet surface excitation (MUSE) typically has an optical sectioning thickness significantly larger than standard physical sectioning thickness, resulting in increased background fluorescence and higher feature density compared to formalin-fixed, paraffin-embedded physical sections. We demonstrate that high-index immersion with angled illumination significantly reduces optical sectioning thickness through increased angle of refraction of excitation light at the tissue interface. We present a novel objective dipping cap and waveguide-based MUSE illuminator design with high-index immersion and quantify the improvement in optical sectioning thickness, demonstrating an e-1 section thickness reduction to 6.67 µm in tissue. Simultaneously, the waveguide illuminator can be combined with high or low magnification objectives, and we demonstrate a 6 mm2 field of view, wider than a conventional 10x pathology objective. Finally, we show that resolution and contrast can be further improved using deconvolution and focal stacking, enabling imaging that is robust to irregular surface profiles on surgical specimens.

Experimental demonstration of broadband negative refraction at visible frequencies by critical layer thickness analysis in a vertical hyperbolic metamaterial

Abstract This work presents a vertical hyperbolic metamaterial (vHMM) consisting of a vertically stacked metal-dielectric multilayer that operates in the visible spectrum. The vHMM is designed by exploiting the relation between negative refraction and effective permittivity along the perpendicular direction of the layers (ε ⊥). When a vHMM has a high loss tangent defined by tan δ ⊥ ≡ Im(ε ⊥)/Re(ε ⊥), even a vHMM composed of relatively thick layers can generate negative refraction. A fabricable vHMM composed of gold and copolymer resist (EL8) which exhibits negative refraction at the wavelengths between 450 and 550 nm is designed using critical layer thickness analysis. The largest negative refraction is observed at the wavelength of 500 nm, where the angle of refraction reaches −1.03°. The corresponding loss tangent and equivalent refractive index are 1.08 and −0.47, respectively. However, negative refraction is not observed at the wavelengths longer than 550 nm due to low tan δ ⊥. We uncover that the tan δ ⊥ of a vHMM is the dominant condition for generating negative refraction rather than the ratio of layer thickness to wavelength.

Theoretical approach on the critical depth of cut of single crystal MgF2 and application to a microcavity

Optical microcavity, which can localize light at a certain spot for a short period of time, has a wide range of applications, such as optical signal processing and optical frequency combs. Single crystal CaF2 has excellent optical properties and many research on the manufacturing process to create a microcavity has been done. However, due to its unstable thermal conditions, stable oscillation of Kerr comb could not be done. Single crystal MgF2, which also has excellent optical properties, has stable thermal conditions suitable to create a microcavity. Like CaF2, MgF2 microcavity can only be manufactured by ultra-precision cylindrical turning, yet its appropriate processing conditions is not known. In this study, a method to derive the critical depth of cut theoretically in ductile mode machining was proposed in consideration of specific cutting energy, mechanical properties and slip system of workpiece, and tool geometry. The critical depth of cut calculated by the proposed method roughly agreed with the experimental value on the MgF2 plane. Unlike CaF2, MgF2 has an optical anisotropy; therefore, in order to create a microcavity where the refractive angle is constant, the resonance part needs to be made on a cylinder with (001) plane as end face. Therefore, a microcavity was fabricated according to the critical depth of cut on a cylinder with (001) as end face derived from the proposed method, and the surface integrity was evaluated from the viewpoint of microcavity performance.

Рефракційне подовження траєкторії оптичного сигналу на трансатмосферній трасі

Aim. The aim of this work is to improve the accuracy of methods for calculating the tropospheric delay caused by the refractive lengthening of the satellite laser rangefinder signal trajectory on the transatmospheric path. Method. One of the main factors that reduce the accuracy of measuring the distance to artificial Earth satellites with satellite laser rangefinders is the influence of the inhomogeneous Earth troposphere on the rangefinder propagation characteristics. This effect leads to an additional signal delay on the measured path, firstly, due to the differences in its propagation speed in a non-uniform environment from the speed of light in vacuum, and secondly, due to the refractive lengthening of the signal trajectory due to the effect of refraction, which is a result of this inhomogeneity. The refractive lengthening is the difference between the real length of a signal trajectory (with the tropospheric part curved by the refraction) and the distance from the observation point to the satellite in a straight line. The calculations are based on use of the integral form of the geometric optics’ ray equation. With the help of well-known quadrature formulas, this integral form is reduced to a system of algebraic equations connecting the elongation due to refraction and the length of the tropospheric part of the trajectory. The main idea of the new method is the refusal of the widespread use of simplified analytical models of the tropospheric profile when calculating the ratio for the signal trajectory lengthening. In the proposed variant, this ratio is given as an integrated function along the trajectory for values that take into account the actual state of the tropospheric profile at the time of measuring the distance to the satellite. Results. Relationships are obtained for the refractive lengthening and the length of the tropospheric part of the trajectory, which depend on the integral values along the path, namely, the angles of the terrestrial and photogrammetric refraction. Scientific novelty and practical importance. The proposed relations make it possible to determine the refractive elongation through the angles of refraction, which take into account the actual state of the inhomogeneous tropospheric layer for the observed satellite of the Earth immediately at the time of measurements.

A novel scheme to enhance both electromagnetic wave transmission and compressive properties of PMI foam sandwich structures

Aimed to enhance electromagnetic (EM) wave transmission and compressive properties of sandwich structures with FR-4 face sheets and the polymethacrylimide (PMI) foam core, a kind of spoof surface plasmon polaritons (SSPPs) structure realized by gradient metal wire arrays was proposed and inserted into the PMI foam core to form a novel antireflection sandwich structure. The transmission performances under normal and oblique incidence were studied by simulation and experimental methods. The results showed that this sandwich structure can achieve a broadband enhanced transmission in X and Ku bands. The enhanced transmission mechanism was suggested to be the effect of the inserted SSPPs structure which changed the transmission path of EM waves in a local area, increased the interface refraction angle and greatly suppressed reflection of each interface. In addition, compressive properties of the sandwich structures were studied experimentally, and the results showed that compared with normal PMI foam sandwich structure, the compressive strength and the energy absorption per unit volume of the antireflection sandwich structure were increased by 72% and 60%. The proposed antireflection sandwich structure is more effective and competitive in load bearing and EM wave transmission applications than traditional structures.

Automated Flaw Detection in Multi-channel Phased Array Ultrasonic Data Using Machine Learning

Modern ultrasonic inspections utilize ever-richer data-sets made possible by phased array equipment. A typical inspection may include tens of channels with different refraction angle, that are acquired at high speed. These rich data sets allow highly reliable and efficient inspection in complex cases, such as dissimilar metal or austenitic stainless steel welds. The rich data sets allow human inspectors to detect cracks with low signal-to-noise ratio from the wider signal patterns. There’s a clear trend in the industry to even richer data sets with full matrix capture (FMC) and related techniques. Convolutional neural networks have recently shown capability to detect flaws with human level accuracy in ultrasonic signals at the B-scan level. To enable automated flaw detection at human-level accuracy for critical applications, these neural networks need be developed to take advantage of today’s rich phased array data-sets. In the present paper, we extend previous work and develop convolutional neural networks that perform highly reliable flaw detection on typical multi-channel phased array data on austenitic welds. The results show, that the modern neural networks can accommodate the rich ultrasonic data and display high flaw detection performance.

Double refraction of electron spin across a metal-semiconductor junction with Rashba and Dresselhaus spin-orbit interactions: A stronger spin-filtering effect

The reflection and refraction of electrons across a two-dimensional metal-semiconductor tunnel junction are studied incorporating both Rashba and Dresselhaus spin-orbit interactions for the semiconductor region. The effects of incident electron energy , angle of incidence and spin-orbit interactions on the angles of refraction of the spin-up and spin-down electrons are calculated exactly. It is shown that the Dresselhaus interaction decreases the angle of refraction for the spin-down electrons more than the spin-up electrons causing a larger splitting between the spin-up and spin-down electrons. Also an increase in the incident energy is shown to increase the spin-filtering effect. The refraction coefficients, spin-up and spin-down current densities and tunnelling conductance are also studied with respect to spin-orbit interactions. Finally, the spin polarization current is determined in the semiconductor region in the presence of Rashba interaction alone and in the presence of both Rashba and Dresselhaus interactions. • Tunneling of electrons across a 2D metal-semiconductor junction is considered. • Rashba and Dresselhaus interactions are incorporated only for semiconductor region. • Reflection and refraction of spin-up and spin-down electrons are calculated exactly. • Dresselhaus interaction enhances the splitting between up- and down-spin electrons. • Spin polarization current is also determined in semiconductor region.

Electromagnetic Wave Scattering from a Moving Medium with Stationary Interface across the Interluminal Regime

This paper extends current knowledge on electromagnetic wave scattering from bounded moving media in several regards. First, it complements the usual dispersion relation of moving media, ω(θk) (θk: phase velocity direction, associated with the wave vector, k), with the equally important impedance relation, η(θS) (θS: group velocity direction, associated with the Poynting vector, S). Second, it explains the interluminal-regime phenomenon of double-downstream wave transmission across a stationary interface between a regular medium and the moving medium, assuming motion perpendicular to the interface, and shows that the related waves are symmetric in terms of the energy refraction angle, while being asymmetric in terms of the phase refraction angle, with one of the waves subject to negative refraction, and shows that the wave impedances of the two transmitted waves are equal. Third, it generalizes the problem to the case where the medium moves obliquely with respect to the interface. Finally, it highlights the connection between this problem and a spacetime modulated medium.

Dealing with the problem of interference in thin films on the basis of the refined unambiguous angles of incidence, reflection, and refraction

This paper addresses the problem of interference in thin films on the basis of the refined unambiguous angles of incidence, reflection, and refraction disclosed earlier by the author with simultaneous use of the generalized vectorial laws of reflection and refraction reported by the author in 2005. Novel unambiguous expressions for the optical path difference between two adjacent reflected (refracted) rays in the reflected (transmitted) system have been achieved and they ultimately led to the development of novel unambiguous conditions for brightness and darkness of interference fringes in the reflected (transmitted) system. The cases of both parallel-sided as well as wedge-shaped films have considered for dealing with the relevant problem.

Ультразвуковой контроль дефектов металлических изделий сложной формы

Nowadays, automation is an actual issue in the development of methods and equipment for ultrasonic non-destructive testing. The conditions of modern industrial production require the development and application the automated testing equipment which is versatile to a wide range of manufactured products, which can have a complex shape. In this paper, we propose a technique for ultrasonic testing of complex-shaped objects. Such technique implies the application of six degrees of freedom robotic manipulators to ensure the required refraction angle of ultrasonic waves into the test object at each measuring position. The trajectory of the robot movement during scanning is provided by restoring the surface profile of the test object using optical profilometry and determining the location of the test object relative to the robotic manipulator using a probe tip. Within the framework of this work, the effectiveness of the developed technology is verified experimentally.

Optoelectronic and photonic properties of π-conjugated benzonitrile derivative bis-Schiff base by solution technique

In the present study, FT-IR and UV spectra of the 4,4′-((1,4 phenylenebis(methaneylylidene))bis(azaneylylidene))dibenzonitrile denoted as, PMAD were investigated in solution phase. PMAD exhibits two absorption bands near UV region. 1,4-Dioxane solvent gives rise to large shift in infrared frequency by the way of dipole-induced dipole interaction type. Optoelectronic and photonic properties were investigated experimentally in 1,4-dioxane, chloroform and THF solvents by solution technique. The significant parameters such as molar/mass extinction coefficient, optical band gap, transmittance, refractive index, angle of incidence and refraction, contrast, molecular absorption cross-section, dielectric constant, loss factors, optical and electric conductance were determined experimentally in 1,4-dioxane, chloroform and THF solutions of PMAD. It is observed that the investigated parameters are sensitive to the solvent. The results indicate that PMAD is promising molecule for electronic and optoelectronic devices.

Numerical-analytical method for calculating the refraction of radio waves in a chaotic upper atmosphere

An operational method is proposed for calculating the refraction of decameter radio waves in a randomly-inhomogeneous upper atmosphere. The method is based on the numerical-analytical solution of stochastic equations of geometric optics. An integral expression is obtained for the dispersion of the refraction angle of a radio wave on the atmospheric path using the approximation of the perturbation method. For a quick calculation of the statistical moment of the refraction angle, the integral expression is reduced to an ordinary first-order differential equation. Joint numerical solution of the unperturbed ray equations and the equations for the statistical moment allows an operational estimate of beam width of radio waves arriving at the observation point. The results of numerical calculations of the standard deviations of the refraction angles of radio waves on paths of various lengths are presented.

The precise role of UV exposure time in controlling the orbital transition energies, optical and electrical parameters of thermally vacuum evaporated Se50Te50 thin film

Abstract The scenarios for this work have been summarized in the preparation of the Se50Te50 thin film -(~500 nm)- by thermal evaporation method, then using a mercury lamp with a 150 W/cm2 as a source of ultraviolet radiation. The irradiation process has been carried out in the open air for the Se50Te50 thin film without irradiation and in the UV-treated period between 0.5 and 2.5 h. A thorough study has been carried out which ultimately has been confirmed from it that the irradiation time plays the role of controlling the optical and electrical properties. The energy band type corresponding to the orbital transitions has been determined, and the energies of the orbital transition has been calculated in the Tauc region, HOMO/LUMO gap, and charge transfer gap. In addition to, calculating the exciton and Urbach energies. It has been found that these energies decrease with increasing UV exposure time, except for Urbach's energies, which behave differently. The role of the UV exposure time in controlling many optical constants, dispersion, and dielectric parameters was investigated. Thin-film quality coefficient, the surface resistance, and thermal emission, in addition to the angle of refraction as a function of wavelength, have been determined. As well, the spectral distribution of the molar parameters has been discussed. Finally, the DC electrical conductivity, the activation energy in the extended and hopping state regions, and Mott's parameters have been computed.

Optical topological transition and refraction control in crystal quartz by tilting the optical axis

Optical topological transition of iso-frequency surfaces strongly modifies the propagation behavior within media. However, in most previous studies, optical topological transition was achieved by tuning the frequency. In this paper, we achieve optical topological transition at fixed frequencies by tuning the direction of the optical axis in crystal quartz. Also, according to the energy flow method, we calculate the refractive angle within the crystal quartz. The calculated results show that both positive and negative refraction can be realized by tuning the direction of the optical axis in the crystal quartz. This optical topological transition in crystal quartz by tilting the optical axis might have potential applications in refraction controlling, spontaneous emission engineering, thermal emission engineering, and phonon polariton engineering.

Programmable nonreciprocal meta-prism

Optical prisms are made of glass and map temporal frequencies into spatial frequencies by decomposing incident white light into its constituent colors and refract them into different directions. Conventional prisms suffer from their volumetric bulky and heavy structure and their material parameters are dictated by the Lorentz reciprocity theorem. Considering various applications of prisms in wave engineering and their growing applications in the invisible spectrum and antenna applications, there is a demand for compact apparatuses that are capable of providing prism functionality in a reconfigurable manner, with a nonreciprocal/reciprocal response. Here, we propose a nonreciprocal metasurface-based prism constituted of an array of phase- and amplitude-gradient frequency-dependent spatially variant radiating super-cells. In conventional optical prisms, nonreciprocal devices and metamaterials, the spatial decomposition and nonreciprocity functions are fixed and noneditable. Here, we present a programmable metasurface integrated with amplifiers to realize controllable nonreciprocal spatial decomposition, where each frequency component of the incident polychromatic wave can be transmitted under an arbitrary and programmable angle of transmission with a desired transmission gain. Such a polychromatic metasurface prism is constituted of frequency-dependent spatially variant transistor-based phase shifters and amplifiers for the spatial decomposition of the wave components. Interesting features include three-dimensional prism functionality with programmable angles of refraction, power amplification, and directive and diverse radiation beams. Furthermore, the metasurface prism can be digitally controlled via a field- programmable gate array (FPGA), making the metasurface a suitable solution for radars, holography applications, and wireless telecommunication systems.

Broadband, frequency-independent acoustic metasurfaces through inverse design

The recent development of acoustic metasurfaces has broadened the capabilities of wave engineering devices with a compact profile. However, the application of acoustic metasurfaces in many scenarios has been limited by their bandwidths. In this work, we report the realization of broadband acoustic metasurfaces that deliver frequency-independent functionalities. Three examples are demonstrated, namely beam steering, focusing and acoustic levitation with fixed refraction angle, constant focal depth and stable levitation. This is achieved by analyzing the requirement of each functionality and engineering the dispersion of the unit cells. The architecture of the unit cells is obtained through inverse design and each unit cell displays a unique dispersive response outlined by the theoretical requirements. The designed metasurface is experimentally verified and we demonstrate a fractional bandwidth of around 100% for all three functionalities. We also attempt to reveal the mechanism for such broadband by characterizing the behavior of representative unit cells.

Reflection and refraction of an electron spin at the junction between two quasi-two-dimensional regions with and without spin-orbit interaction

We derive the reflection and refraction laws for an electron spin incident from a quasi-two-dimensional medium with no spin–orbit interaction on another with both Rashba and Dresselhaus spin–orbit interaction using only energy conservation. We obtain the well-known result that for an incident angle, there can be generally two different refraction angles for refraction into the two spin eigenstates in the refraction medium, resulting in two different ‘spin refractive indices’ and two critical angles for total internal reflection. We derive expressions for the spin refractive indices, which are not constant for a given medium but depend on the incident electron’s energy. If the effective mass of an electron in the refraction medium is larger than that in the incidence medium, then we show that for some incident electron energies and potential barrier at the interface, the spin refractive index of the incidence medium can lie between the two spin refractive indices of the refraction medium, resulting in only one critical angle. In that case, if the incident angle exceeds that critical angle, then refraction can occur into only one spin eigenstate in the refraction medium. If the system is engineered to make this happen, then it will be possible to obtain a very high degree of spin-polarized injection into the refraction medium. The amplitudes of reflection of the incident spin into its own spin eigenstate and the orthogonal spin eigenstate (due to spin flip at the interface), as well as the refraction amplitudes into the two spin eigenstates in the refraction medium are derived for an incident electron (with arbitrary spin polarization and incident energy) as a function of the angle of incidence.