Arbitrary Angle Of Incidence Research Articles

Acoustic radiation force on a cylindrical particle near a planar rigid boundary II. – Viscous fluid cylinder example and inherent radiation torque

ObjectiveThis study extends the scope of a previous analysis on the time-averaged acoustic radiation force on a rigid (sound impenetrable) cylinder near a flat boundary [F.G. Mitri, J. Phys. Commun. 2 (2018) 045019] to the case of a viscous compressible fluid (sound penetrable) particle, and determine the time-averaged acoustic radiation torque as well. Motivation and noveltyPrevious analytical formalisms did not consider the case of a sound penetrable cylindrical particle insonified at an arbitrary angle of incidence (in the polar plane) near a reflecting boundary. This work fills this gap, and provides exact expressions and computations for the acoustic radiation force and torque components. MethodThe partial-wave series expansion method, in conjunction with the method of images and the translational addition theorem of cylindrical wave functions are used to derive the analytical expressions for the longitudinal and transverse acoustic radiation force components. Moreover, the emergence of a radiation torque that causes the particle to rotate around its center of mass is computed using an exact partial-wave series expression. Results, key conclusion and some perspectivesAttractive (pulling), repulsive (pushing) and neutral (zero) forces arise depending on the particle-boundary distance, the cylinder size parameter as well as the angle of incidence (in the polar plane) of the insonifying waves. Emphasis is also given on the emergence of an acoustic radiation torque (that vanishes for a rigid or non-viscous circular cylinder). Computations for the axial radiation torque efficiency anticipate the generation of positive radiation torque, its reversal, in addition to a zero efficiency, leading, respectively, to counter-clockwise, clockwise or lack of particle rotation as the angle of the incident waves deviates from normal incidence with respect to the boundary surface. The extension to the case of an elliptical/oval cylinder near a boundary is mentioned, and replies to some misleading and obtuse comments on the paper [F.G. Mitri, Phys. Fluids 28 (2016) 077104] are provided.

Laser-induced periodic surface structures: Arbitrary angles of incidence and polarization states

We demonstrate that the finite-difference time-domain (FDTD) method can be used to study the formation of laser-induced periodic surface structures (LIPSSs) under oblique incidence and arbitrary polarization states. The inhomogeneous energy absorption below a rough surface at oblique incident angle is studied by the FDTD method and compared to the analytical efficacy theory developed by Sipe et al. [Phys. Rev. B 27, 1141 (1983)10.1103/PhysRevB.27.1141]. The two approaches show excellent agreement. The surface topographies of both low-spatial-frequency LIPSSs (LSFLs) and high-spatial-frequency LIPSSs (HSFLs) at oblique incidence and various polarization states (linear, circular, radial, and azimuthal) are simulated by taking into account topography-driven interpulse feedback effects. For s- and mixed s- and p-polarized beams at large incident angles, the simulated LSFLs show orientations that are neither perpendicular nor parallel to the laser polarization. Their physical origin is explained by a nonzero angle between the in-plane wave vector of the incident light and the scattered light. By using circularly-polarized beams, the simulated surface topographies are further shown to be in excellent agreement with the triangular LSFLs and the fine-dot nanoscaled structures reported in the literature. In addition, the simulation of HSFLs suggests that their periods have almost no dependence on the incident angle nor the polarization angle, while their surface topographies resemble that of blazed gratings at large incident angles for p-polarized and mixed s- and p-polarized beams. The origin is explained by the appearance of asymmetry in the scattered near-field light. The extension to oblique incidence and arbitrary polarization states demonstrates that the FDTD approach on LIPSSs is a highly versatile and powerful technique which has the potential to be one of the foundations for a complete modeling and understanding of LIPSSs under various irradiation conditions.

Four-Dimensional Characteristic Matrix for Electromagnetic Coupling of Multilayer Sub-Wavelength Metasurface System

In this article, we propose a 4-D characteristic matrix theory for the electromagnetic coupling of the multilayer metasurface system. The multilayer metasurface system is generally composed of periodic sub-wavelength metallic elements printed on the substrates. In the system, not only the coupling between multilayer metallic elements but also the coupling between different polarized waves can exist. In order to analyze the couplings and determine the total transmission (reflection) characteristic, a series of 4-D characteristic matrices are established for the substrates and metallic elements to relate the total tangential fields (two electrical components and two magnetic components) at adjacent interfaces. Finally, a four-layer metasurface system is designed to verify the theory whose results agree well with the simulated ones at arbitrary incidence angle. Unlike the existing methods, the four-dimensional characteristic matrix theory is not only independent of the anisotropy of the metallic elements, but also insensitive to the layer number of the metasurface. Thus, the proposed theory holds valid for arbitrary multilayer metasurface system, regardless of the layer number and the metallic elements.

Topologically protected zero refraction of elastic waves in pseudospin-Hall phononic crystals

Zero-angle refraction of elastic waves in metamaterials has attracted attention for its extraordinary wave collimation properties. However, earlier implementations relied on the specific flat equifrequency curve of the phononic crystals suffer from a narrow range of incident angles or operating bandwidths, which severely hinders the exploration and design of functional devices. Here, we propose an elastic near-zero refractive index metamaterial of a triangular lattice to realize topological zero refraction with arbitrary angles of incidence and wide working frequency range. Topological robustness of the zero-angle refraction of pseudospin-Hall edge state against defects is experimentally demonstrated. Furthermore, tunable wave mode conversion associated with the zero-angle refraction is revealed and discussed. These results provide a paradigm for the simultaneous control of the refraction properties of longitudinal and transverse waves that can be employed for designing the topological elastic antennas and elastic wave collimator.

Performance optimization of tandem organic solar cells at varying incident angles based on optical analysis method.

Tandem organic solar cells (OSCs) show great potential due to advantages such as the utilization of wide-spectrum light and low thermalization loss. The current mismatch between sub-cells is one of the major issues reducing the final output efficiency of a tandem device. In this paper, we focus on the current mismatch of tandem OSCs at oblique incidence and aim to reduce its adverse effect on the performances of realistic devices working at varying incident angle. Firstly, we propose an optical analysis method based on the 4×4 matrix formalism to analyze and optimize the performance of tandem solar cells at arbitrary incident angles. Compared with those optimal designs via matching the currents of sub-cells only at normal incidence, the proposed method chooses the optimal structure of the tandem device by maximizing the generated energy density per day with considering the current match at different incident angles during daytime. With the proposed method, a typical tandem organic solar cell is optimized as an example, and the optimized tandem device has a balanced current match at all incident angles during a whole day. Experimental results demonstrate that the generated energy density per day of the optimized tandem device has increased by 4.9% compared to the conventional device optimized only at normal incidence. The proposed method and results are expected to provide some new insights for the performance analysis and optimization of tandem or multi-junction solar cells, especially those devices exhibiting serious current mismatch between sub-cells at varying incident angles in practical applications.

Understanding diffraction grating behavior, part II: parametric diffraction efficiency of sinusoidal reflection (holographic) gratings

With the widespread availability of electromagnetic (vector) analysis codes for describing the diffraction of electromagnetic waves by periodic grating structures, the insight and understanding of nonparaxial parametric diffraction grating behavior afforded by approximate methods (i.e., scalar diffraction theory) is being ignored in the education of most optical engineers today. We show that the linear systems formulation of nonparaxial scalar diffraction theory enables the development of a scalar parametric diffraction grating model [for transverse electric (TE) polarization] for sinusoidal reflection gratings with arbitrary groove depths and arbitrary nonparaxial incident and diffracted angles. This scalar parametric analysis is remarkably accurate as it includes the ability to redistribute the energy from evanescent orders into the propagating ones, thus allowing the calculation of nonparaxial diffraction efficiencies to be predicted with an accuracy usually thought to require rigorous electromagnetic theory. These scalar parametric predictions of diffraction efficiency are compared to paraxial scalar and rigorous electromagnetic (vector) predictions for a variety of nonparaxial diffraction grating configurations, thus providing quantitative limits of applicability of nonparaxial scalar diffraction theory to sinusoidal reflection gratings as a function of the grating period-to-wavelength ratio (λ / <italic>d</italic>).

Twisted radiation from nonlinear Thomson scattering with arbitrary incident angle

Thomson/Compton scattering is well-known as a scattering process between electromagnetic radiation and charged particles, which is found in laboratories and nature. Here, we investigate the radiative properties of nonlinear Thomson scattering with arbitrary incident angle. Based on classical electrodynamics, the analytical universal expressions of the electric field and energy spectrum of the radiation emitted by a relativistic electron scattering of circularly polarized laser field are derived. It is shown that the spatial distributions of the radiation energy of high-order harmonics have annular shapes and the symmetry of the annular shapes is strongly affected by the incident angle, which may relate with the angular momentum of twisted high-order harmonics. These results would help the understanding of the properties of twisted γ/X-ray and high energy electron-laser scattering experiments in laboratory.

Phase shift formulas in electro-optical crystals with an arbitrary incident direction

The calculation of the phase shift in electro-optical crystals is related to an extensive range of optical devices. A set of analytical phase shift formulas at arbitrary incidence angle and azimuth angle for a plane-parallel electro-optical crystal plate is derived. This enables us to analyze the phase shift induced by an electro-optical crystal with an arbitrary incident direction. As an example, the derived formulas are used to investigate the influence of incidence angle and azimuth angle on the phase shift in a lithium niobate crystal plate. For the field-free lithium niobate crystal, the phase shift depends only on the incidence angle. In contrast, when an external electric field is applied to the crystal, the phase shift is not only strongly influenced by the incidence angle, but also periodically changes with the azimuth angle. In order to validate the correctness of the derived formulas, the experiments are also conducted. The theoretical results are proved to be in good agreement with the experimental results.

Bound states in the continuum in double-hole array perforated in a layer of photonic crystal slab

We theoretically investigate optical bound states in the continuum (BIC) supported by a double-hole array. It verifies BICs around 0° can be observed only in the structure with symmetrical nanohole shape in one lattice. At arbitrary oblique incident angles, BIC with Q-factors exceeding 106 can be found in the double-hole arrays in both types, which are sensitive to the refractive index of the surrounding medium. Results from both finite-difference time-domain method and temporal coupled mode theory accord well, and they are helpful in the design of novel photonic elements based on BICs, such as sensors, and filters.

Reflection of Plane Acoustic Waves for an Oblique Incidence on a Tellurium Dioxide Crystal Face

This paper describes the phenomenology of the reflection of acoustic body waves in an acoustooptical paratellurite crystal in the case of arbitrary elastic wave incidence on a free interface between the crystal and vacuum. The analysis is performed at arbitrary angles of incidence of acoustic waves in the XOY plane of the material. Anomalous variants of acoustic wave reflection are considered, which fundamentally differ from the known ones and for which the transformation of incident elastic wave energy into reflected wave energy is studied. In the case of oblique incidence, cases of strict reflection of a wave towards the incident wave with an energy conversion efficiency close to 100% are noted.

Fabry-Pérot Huygens' metasurfaces: On homogenization of electrically thick composites

Realization of the anomalous refraction effects predicted by Huygens' metasurfaces (HMS) have required tedious and time-consuming trial-and-error numerical full-wave computations. It is shown herein that these requirements can be alleviated for transverse magnetic (TM) propagation by a periodic dielectric-based HMS consisting of an electrically thick array of cascaded Fabry-P\'erot etalons. This "Fabry-P\'erot HMS" (FP-HMS) is easily designed to mimic the local scattering coefficients of a standard zero-thickness HMS (ZT-HMS) which, according to homogenization theory, should result in the desired anomalous refraction. To probe the characteristics of this practical FP-HMS, a method based on Floquet-Bloch (FB) analysis is derived for predicting the fields scattered from it for arbitrary angles of incidence. This method produces simple closed-form solutions for the FB wave amplitudes and the resulting fields are shown to agree well with full-wave simulations. These predictions and full-wave simulations verify the applicability of homogenization and scattering properties of zero-thickness HMS's to thick structures. They also verify the proposed semi-analytical microscopic design procedure for such structures, offering an effective alternative path to implementation of theoretically envisioned intricate field manipulating devices.

39.1: Invited Paper: Mass Production of Holographic Transparent Components for Wearable Applications

Diffractive optics such as holographic optical elements (HOEs) can provide transparent and narrow band components with arbitrary incident and diffracted angles for near‐to‐eye commercial electronic products for augmented reality (AR), virtual reality (VR), and smart glass applications. In this paper, we will summarize the operational parameters and general optical geometries relevant for near‐to‐eye displays, the holographic substrates available for these applications, and their performance characteristics and ease of manufacture. We will compare the holographic substrates available in terms of fabrication, manufacturability, and end‐user performance characteristics. Luminit is currently emplacing the manufacturing capacity to serve this market, and this paper will discuss the capabilities and limitations of this unique facility.

Metasurface Modeling for the Manipulation of Goos–Hänchen and Imbert–Fedorov Shifts

We derive immittance tensors for the analysis, synthesis, and characterization of linear metasurfaces (MSs) illuminated at arbitrary angles of incidence. Their closed-form expressions are verified for two representative examples using full-wave simulations, and they provide physical insights into the operation of the considered MSs. We use these expressions to study exotic phenomena related to reflection and transmission of electromagnetic waves from these MSs, specifically to tailor Goos-Hänchen and Imbert-Fedorov shifts.

RADIO-WAVES REFLECTION AT REMOTE SENSING OF UNDERLYING COVERS

Monitoring technologies are rapidly developing at present and allow to extract and use non-coordinate information about objects. Noncoordinate information is the information about the type and properties of an object under study. Remote sensing is the main method of solving monitoring problems where special positioning belongs to the radar methods, based on space-time processing of signals and, in particular, on methods of radio polarimetry. It is necessary to have information about the surface in order to solve the monitoring task. The slightest changes in the electrical and physical properties of such areas as salinity, humidity, soil composition, etc. will lead to a change in the basic electrodynamics of the surface, notably its complex dielectric permittivity. The article demonstrates the precise solutions to the problems of radio-waves reflection from a layered surface with various laws of changes of the complex permittivity  in depth. Media with exponential and quadratic laws of variation  for arbitrary angles of incidence of the radio wave on the surface are considered. Precise decision is obtained for layered media with the law of change in the complex permittivity the polynomial and linear characteristics. A similar problem for the parabolic layer is considered separately. The detailed analysis of radio waves reflection from the medium with a matching layer is carried out. The nature of the electromagnetic field inside the transition layer is studied in detail. The article is illustrated by the graphs showing the dependences of an electromagnetic wave reflection coefficient on the layered medium with linear and exponential laws of variation of the complex dielectric constant over depth.

Polarization modeling and predictions for Daniel K. Inouye Solar Telescope part 5: impacts of enhanced mirror and dichroic coatings on system polarization calibration

The Daniel K. Inouye Solar Telescope (DKIST) is designed to deliver accurate spectropolarimetric calibrations across a wide wavelength range and large field of view for solar disk, limb, and coronal observations. DKIST instruments deliver spectral resolving powers of up to 300,000 in multiple cameras of multiple instruments sampling nanometer scale bandpasses. We require detailed knowledge of optical coatings on all optics to ensure that we can predict and calibrate the polarization behavior of the system. Optical coatings can be metals protected by many dielectric layers or several-micron-thick dichroics. Strong spectral gradients up to 60 deg retardance per nanometer wavelength and several percent diattenuation per nanometer wavelength are observed in such coatings. Often, optical coatings are not specified with spectral gradient targets for polarimetry in combination with both average- and spectral threshold-type specifications. DKIST has a suite of interchangeable dichroic beam splitters using up to 96 layers. We apply the Berreman formalism in open-source Python scripts to derive coating polarization behavior. We present high spectral resolution examples on dichroics where transmission can drop 10% with associated polarization changes over a 1-nm spectral bandpass in both mirrors and dichroics. We worked with a vendor to design dichroic coatings with relatively benign polarization properties that pass spectral gradient requirements and polarization requirements in addition to reflectivity. We now have the ability to fit multilayer coating designs which allow us to predict system-level polarization properties of mirrors, antireflection coatings, and dichroics at arbitrary incidence angles, high spectral resolving power, and on curved surfaces through optical modeling software packages. Performance predictions for polarization at large astronomical telescopes require significant metrology efforts on individual optical components combined with system-level modeling efforts. We show our custom-built laboratory spectropolarimeter and metrology efforts on protected metal mirrors, antireflection coatings, and dichroic mirror samples.

Modified model of photonic spin Hall effect of Gaussian beam reflected from a dielectric interface

A modified model for the photonic spin Hall effect when a Gaussian beam is reflected from a dielectric interface is derived. Compared with the former models that generally have great limitations (such as only being applicable to p- and s-polarization; or the approximate p-polarization; or invalid around the Brewster angle), the modified model we derived does not have these limitations, which can be suitable for arbitrary linear incident polarization and arbitrary angle of incidence. Furthermore, the modified model is verified by experiments and the experimental results are in good agreement with theoretical results.

Micro‐cone textures for improved light in‐coupling and retroreflection‐inspired light trapping at the front surface of solar modules

AbstractMicron‐scale textures at the front surface of solar modules have been reported to improve the current generation by both enhancing light in‐coupling as well as by reducing light out‐coupling via back‐reflection, similar to the retroreflective effect. Whereas the general working principle and advantages of these textures have been described previously, here, the interplay of the reflection properties of different substrates with the enhancement effects is analyzed for textures of conical geometry. The study takes into consideration the incident light of arbitrary angle of incidence as well as the overall energy yield. Supported by optical simulations, periodic micro‐cone textures were optimized and prototyped based on direct laser writing and a scalable replication process. Micron‐scale textures with cones of various aspect ratios were examined on mono‐crystalline silicon (c‐Si) solar cells; an optimum aspect ratio of 0.73 was identified. This moderate aspect ratio is suitable for large‐scale replication, while showing near‐zero surface reflection and excellent light trapping. An increase in energy yield of up to 8% was calculated for the case of micro‐cone textures at the front surface of commercial alkaline‐etched c‐Si solar cells. Moreover, the excellent optical properties of the micro‐cone textures were highlighted by improving the power conversion efficiency (PCE) of a Cu(In,Ga)Se2 (CIGS) thin‐film solar cells from 20.2% to 20.9%. A comparable PCE improvement has been achieved by conventional MgF2 antireflection coatings, but the angular stability and in turn the energy yield of the micro‐cone textures is much higher.

Highly efficient GaN-based high-power flip-chip light-emitting diodes

High-power flip-chip light-emitting diodes (FCLEDs) suffer from low efficiencies because of poor p-type reflective ohmic contact and severe current crowding. Here, we show that it is possible to improve both the light extraction efficiency (LEE) and current spreading of an FCLED by incorporating a highly reflective metallic reflector made from silver (Ag). The reflector, which consists of an Ag film covered by three pairs of TiW/Pt multilayers, demonstrates high reflectance of 95.0% at 460 nm at arbitrary angles of incidence. Our numerical simulation and experimental results reveal that the FCLED with Ag-based reflector exhibits higher LEE and better current spreading than the FCLED with indium-tin oxide (ITO)/distributed Bragg reflector (DBR). As a result, the external quantum efficiency (EQE) of FCLED with Ag-based reflector was 6.0% higher than that of FCLED with ITO/DBR at 750 mA injection current. Our work also suggests that the EQE of FCLED with the Ag-based reflector could be further enhanced 5.2% by replacing the finger-like n-electrodes with three-dimensional (3D) vias n-electrodes, which spread the injection current uniformly over the entire light-emitting active region. This study paves the way towards higher-performance LED technology.

Seismic response analysis of the reef-seawater system under incident SV wave

The seismic response analysis of a reef engineering site is the foundation for the seismic design of artificial islands and other upper constructions. This study proposes a two-dimensional seismic analysis model for the reef-seawater system, where the fluid-solid coupling effect is considered and the wave radiation effects of infinite fluid and solid domains are simulated by corresponding artificial boundary conditions. Meanwhile, the seismic wave input method based on the substructure of artificial boundaries is modified to accomplish the process of inputting the seismic waves with arbitrary incident angles into the calculation region. The accuracy of the proposed model is verified by numerical examples. Afterwards, we conduct the parametric studies and the seismic analysis of a series of practical layered reef models. The results indicate that the least favorable slope gradient for the seismic response is generally at approximately 30°, and the feature of wave velocity reduction along the vertical direction significantly magnifies the seismic response on the reef flat. The peak acceleration ratio near the edges of the reef flat distributes between 3 and 4. While in the middle area, it is usually between 1.5 and 2.5, and can reach up to 4 when the width of reef flat decreases.

Neutralization energy contribution to the nanostructure creation by the impact of highly charged ions at arbitrary angle of incidence upon a metal surface covered with a thin dielectric film

We consider the cascade neutralization of highly charged ions in the interaction with metal-dielectric film surface at moderate ionic velocities and arbitrary angle of incidence. We use the recently developed micro-staircase model based on the quasi-resonant two-state vector model to obtain the final ionic charge in front of the metal surface and calculate the corresponding neutralization energy. Within the framework of the model, the electrons are captured from the metal into the particular ionic Rydberg states inside the dielectric.We discuss the interplay of the collision geometry and surface parameters in the neutralization process for the ArZ+, KrZ+ and XeZ+ ions. It is demonstrated that the equal neutralization energies can be achieved for different combinations of the angles of incidence and dielectric constants of the film. From the equi-neutralization curves we examine the film properties for the particular collision geometry, for which the neutralization energy (together with the deposited kinetic energy) is sufficient for the formation of the surface nanostructure (crater) of a given size. The corresponding threshold values of the dielectric constants are recognized.