Arbitrary Polarization Direction Research Articles

Natural frequency analysis of laminated piezoelectric beams with arbitrary polarization directions

Natural frequency analysis of laminated piezoelectric beams with arbitrary polarization directions

A Photoconductive Terahertz Radiation Source Generating Terahertz Waves with Arbitrary Polarization Direction

A Photoconductive Terahertz Radiation Source Generating Terahertz Waves with Arbitrary Polarization Direction

An Algorithm for Fast Simulation of CW Illuminator

The continuous wave (CW) illuminator is aimed to simulate high-altitude nuclear electromagnetic pulse. In this article, a simulation algorithm is proposed covering the method of moments and finite difference method (FDM), with the high-speed simulation of the CW illuminator with arbitrary ellipse size, arbitrary loading, and arbitrary polarization direction. Based on the surface electric field equation of the CW illuminator, the mathematical model is established with the vector potential equation and the boundary conditions. In this model, the pulse function and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\delta$</tex-math></inline-formula> function are set as the basis function and the weight function, respectively, for the establishment of the current equation, with the current distribution determined by the simplification equation with image theory and nonuniform FDM. Finally, as the field distribution is determined by the superposition theorem. The simulation algorithm is verified by the self-built CW illuminator.

Impact of an interface electrode charge and materials polarization to a conductive interface crack

A charged interface electrode and a conductive interface crack between different piezoelectric half-spaces with an arbitrary polarization direction under out-of-plane mechanical loading and in-plane electrical field are considered. An analytical method is used based upon the presentations of the electromechanical characteristics through sectionally-analytic vector-functions with the following formulation and solution of the combined Dirichlet-Riemann boundary value problem. Special attention is devoted to the formulation of the Gauss theorem for the electrode, which permits to take into account its charge. The expressions for stress, electric field, electric displacement jumps and the energy release rate (ERR) are found in a simple analytical form. The numerical results show the dependence of the ERR on the electrode charge, on the intensity of the electric field and on the directions of the polarization of the piezoelectric materials. It is particularly found that due to the appropriate choice of these parameters, the maximum value of the ERR for the crack can be substantially reduced, which mitigates the threat of crack propagation.

Study of symmetries of chiral metasurfaces for azimuth-rotation-independent cross polarization conversion.

The realization of cross-polarization conversion has attracted great interest in polarization conversion metasurfaces (PCMs), particularly due to polarization manipulation of electromagnetic (EM) waves with small size and low loss. An azimuth-rotation-independent (ARI) cross-polarization converter is a kind of 90° polarization rotator, which can rotate the polarization of linearly polarized incident electromagnetic (EM) waves with an arbitrary polarization direction to the orthogonally polarized transmitted EM waves. In this paper, we study the symmetry properties of chiral metasurfaces using the Jones matrix method for ARI 90° polarization rotators. The previous designs could only address C4 symmetry, but with this approach, the derived unit cell structure of the ARI PCM should possess Cn(n ≥ 3, n ∈ N+) symmetry. To confirm the design concept, two chiral structures with different symmetries are investigated by full-wave numerical simulations. The experimental results are also carried out and excellently agree with the simulated results. It could be used for polarization conversion applications and further utilized in antenna applications, polarization detection, and telecommunication applications.

Propagation of double zero-order Bessel beam and its scattering properties to uniaxial anisotropic spheres

Based on the generalized Lorenz Mie theory, the propagation and scattering properties of a uniaxial anisotropic spherical particle illuminated separately by double zero-order Bessel beam with arbitrary propagation direction and polarization direction are studied. The propagation and scattering characteristics are compared with those of a uniaxial anisotropic spherical particle illuminated by a single zero-order Bessel beam. Using the orthogonal relation of the spherical vector wave function and coordinate rotation theorem, the expanded forms of double zero-order Bessel beams with arbitrary propagation direction and polarization direction are derived. The analytical expressions of the expansion coefficients are derived by the integral method. The expansion coefficients of total incident field are obtained through the vector superposition principle. Based on the Fourier transform and tangentially continuous boundary conditions, the internal electromagnetic field of the uniaxial anisotropic sphere is expanded in terms of the spherical vector wave function and the scattering coefficients are derived. By comparing the angular distribution of the radar cross section of the particle illuminated by single and double zero-order Bessel beam when degenerating into plane waves with those results given by the literature, the correctness of the theory and the program in this paper are both verified. The effects of the incidence angle, conic angle and polarization angle on angle distribution of the radar cross section are numerically analyzed. The theoretical and numerical results in this paper are expected to be used to study the scattering properties, particle size analysis and optical trapping for anisotropic particles, biological cells and other particles illuminated by multi-beams.

Spin-orbit Torque Switching of Perpendicular Magnetization in Ferromagnetic Trilayers

In ferromagnetic trilayers, a spin-orbit-induced spin current can have a spin polarization of which direction is deviated from that for the spin Hall effect. Recently, magnetization switching in ferromagnetic trilayers has been proposed and confirmed by the experiments. In this work, we theoretically and numerically investigate the switching current required for perpendicular magnetization switching in ferromagnetic trilayers. We confirm that the tilted spin polarization enables field-free deterministic switching at a lower current than conventional spin-orbit torque or spin-transfer torque switching, offering a possibility for high-density and low-power spin-orbit torque devices. Moreover, we provide analytical expressions of the switching current for an arbitrary spin polarization direction, which will be useful to design spin-orbit torque devices and to interpret spin-orbit torque switching experiments.

Antiferromagnetic Oscillators Driven by Spin Currents with Arbitrary Spin Polarization Directions

Antiferromagnetic (AFM) oscillators are of interest because of their potential to operate at THz frequencies, and thus to fill the ``terahertz gap''. Previous studies on AFM oscillators have focused on using the spin Hall effect to generate spin current, but other mechanisms exist. Here the authors investigate using spin current with an arbitrary polarization direction that is not simply due to the spin Hall effect. Their results will be useful for application of such oscillators, and more broadly for understanding AFM spin dynamics.

A hybrid method for shielding effectiveness estimation of a perforated enclosure against planewave excitation

ABSTRACTThis paper develops a hybrid model based on the combination of full-wave simulation method and circuit model analytic algorithm, which can predict the shielding effectiveness of a perforated rectangular enclosure irradiated by a planewave with arbitrary incident and polarization direction. In order to take the effect of the electromagnetic losses of the aperture into account, the full-wave simulation method is adopted to calculate the coupling voltage of the aperture. The circular aperture or rectangular aperture with arbitrary length–width ratio can be positioned anywhere in the front panel of the enclosure. Taking the effect of the thickness into account, we establish the equivalent circuit model of the perforated enclosure with aperture coupling voltage as an equivalent voltage source. Then, the TEmn and TMmn modes of the coupling electric field at arbitrary observation point within the enclosure are calculated based on waveguide theory. Simulation results of the hybrid model are in good agreement with those of transmission line matrix method within the frequency range of 0–3 GHz. Solution times using the hybrid model are far less than those required by pure numerical methods.

Photodetachment of hydrogen negative ion near inelastic surfaces: Arbitrary laser polarization direction

The photodetachment of hydrogen negative ion near different inelastic surfaces is investigated by the semiclassical closed orbit theory for arbitrary laser polarization direction . A two‐term formula of photodetachment cross section consisting of a smooth background term and an oscillatory term is derived. The oscillatory term contains an extra angular factor that describes the dependence of oscillations in total cross section on the laser polarization direction. It is observed that the amplitude of oscillations in cross section reaches maximum at when laser polarization is parallel to the z‐axis and it approaches zero as the laser polarization direction becomes perpendicular to the z‐axis. It is also observed that as the reflection coefficient , which accounts for the inelastic behavior of the surfaces, increases the amplitude of oscillation also increases. © 2015 Wiley Periodicals, Inc.

Photodetachment of H− near a hard wall with arbitrary laser polarization direction

The photodetachment of H− near a hard wall is investigated with linear polarized laser light travelling in arbitrary direction θL with respect to the z axis. An analytical formula for the total cross section is derived using semi-classical closed orbit theory, which consists of two terms, i.e., the smooth background term and the oscillatory term with an extra factor 2(θL). This factor controls oscillations in the total photodetachment cross section. The amplitude of oscillation is maximum at θL = 0 when the laser polarization direction is perpendicular to the wall and it approaches zero at θL = π /2 when the laser polarization direction is parallel to the wall. It is also observed that the total cross section depends on the source–wall distance and it reduces to a free space case when the wall is at infinite distance from the source.

Simultaneous formation of ablative and thermochemical laser-induced periodic surface structures on Ti film at femtosecond irradiation

Formation of laser-induced periodic surface structures (LIPSS) on the titanium surface at the presence of sharply focused fs radiation exhibits two different regimes. Conventional ablative LIPSS with low regularity are oriented orthogonally to the polarization direction of the incident beam, while thermochemical LIPSS with highly uniform periodicity are oriented along the polarization direction. These two types of LIPSS can co-exist and influence each other for arbitrary polarization and beam scanning directions. The observed regimes help to clarify mechanisms of LIPSS formation, as well as to form LIPSS of specific shapes and degrees of regularity.

Scattering of a Uniaxial Anisotropic Sphere Located in Dual Gaussian Beam with Arbitrary Propagation Directions

The scattering characteristics of a uniaxial anisotropic sphere illuminated by two Gaussian beams with arbitrary propagation and polarization directions are investigated. On the basis of spherical vector wave functions and coordinate rotation theory, the fields of any incident Gaussian beam with arbitrary propagation and polarization directions are expanded in terms of the spherical vector wave functions. Then the total expansion coefficients of the incident fields are derived by superposition of the vectors. Based on the Fourier transform and boundary conditions, the analytical expressions of the scattering coefficients of dual Gaussian beams with arbitrary propagation directions by a uniaxial anisotropic sphere are obtained. The effects of the incident angle, polarization angle of the dual Gaussian beams on the angle distributions of the radar cross sections (RCSs) are numerically analyzed in detail. This investigation may provide an effective test for further research on the scattering characteristic of anisotropic particles by a multiple beams and radiation forces, which are important in optical tweezers and related particle manipulation applications.

A 2D FDTD Algorithm for Whole-Hemisphere Incidence on Periodic Media

We present a modified version of the 2D split-field finite difference time domain (FDTD) method which enables efficient simulation of periodic structures. Our algorithm allows for broadband, whole-hemisphere oblique incidence sources with structures that are inhomogeneous in permittivity, conductivity, and permeability. The structures considered are of finite extent in one dimension, periodic in a second orthogonal dimension, and uniform (or homogeneous) in a third dimension. With prior FDTD methods, this required a full 3D simulation space. In this work, we reduce the modeling space from a 3D grid to a 2D grid, while still allowing incident waves to be oblique with respect to that dimension. We derive this new algorithm beginning with a complete source definition that allows for arbitrary polarization and incidence direction. The key update equations are found, and we also give a method for finding the full vectorial far-field orders from the simulation output. We validate the method by simulating an etalon, a Bragg grating, and a photonic band gap structure.

Selection rules and linear absorption spectra of carbon nanotubes in axial magnetic fields

We derive a transparent and easy-to-use analytic expression for the selection rules and the optical dipole matrix elements for carbon nanotubes of arbitrary chirality in the presence of axial magnetic fields using a single-orbital \ensuremath{\pi}-electron tight-binding model. From this, we calculate the linear absorption spectrum for arbitrary polarization directions of the incident light, providing insight into all optically allowed transition. We show that the transverse absorption peaks can be selectively excited with circularly polarized light and spectrally resolved in an axial magnetic field.

Reflective Liquid Crystal Polarization Rotator with Ultraviolet-Polymerizable Liquid Crystal Retardation Film

We demonstrate a reflective liquid crystal (LC) polarization rotator with a UV-polymerizable LC retardation film inside an LC cell. The LC polarization rotator consists of two birefringence layers; one layer is a UV-polymerizable LC film that acts as a quarter-wave plate and the other is a nematic LC layer that acts as an electrically tunable retardation film. The polarization direction of the linearly polarized incident light is found to rotate in a sufficient angular range of 2π, depending on the retardation of the electrically tunable LC layer. Additionally, good polarization rotation properties are achieved for an arbitrary polarization direction of the incident light. The influence of the error of the retardation from the designed value on the polarization rotation properties is investigated in detail. The polarization rotation function is found to slightly deteriorate with an increase in the retardation error of the UV-polymerizable LC film, whereas the ellipticity of the output light is sensitively enhanced with an increase in the retardation error of the quarter-wavelength plate.

Griffith's crack in a 2-D piezoelectric domain with an arbitrary polarization direction: Analytical/X-FEM solution

The analytic solution for Griffith's crack in an infinite 2-D piezoelectric domain is obtained for arbitrary polarization direction. The analytical approach considered here is simple and different from the existing methodology (where the solutions are firstly obtained for an elliptical void and then degenerated to Griffith's crack solution). The obtained results have shown that intensity factors (IFs) are independent of the polarization direction for Griffith's crack in an infinite 2-D piezoelectric domain. The solution for a polarization perpendicular to the crack is also obtained and validated with existing results. The results of IFs are also obtained numerically using extended finite element method (X-FEM). It is observed that IFs for a finite specimen is polarization direction dependent.

Calculation of radiation force and torque exerted on a uniaxial anisotropic sphere by an incident Gaussian beam with arbitrary propagation and polarization directions

On the basis of spherical vector wave functions and coordinate rotation theory, the expansion of the fields of an incident Gaussian beam with arbitrary propagation and polarization directions in terms of spherical vector wave functions is investigated, and beam shape coefficients are derived. Using the results of electromagnetic scattering by a uniaxial anisotropic sphere, the analytical expressions of the radiation force and torque exerted on a homogeneous absorbing uniaxial anisotropic sphere by the arbitrary incident Gaussian beam. We numerically analyze and discuss the following: the effects of an anisotropic absorbing dielectric on the axial and transverse radiation forces exerted by an off-axis Gaussian beam on a uniaxial anisotropic sphere; the variations in the axial, transverse, and resultant radiation forces (with incident angle β and polarization angle α) imposed by an obliquely Gaussian beam on a uniaxial anisotropic sphere; and the results on the characteristics of the three components of the radiation forces versus the center-to-center distance between the sphere and beam. Selected numerically results on the radiation torque exerted on a stationary uniaxial anisotropic transparent or absorbing sphere by a linearly polarized Gaussian beam are shown, and the results are compared with those exerted an isotropic sphere. The accuracy of the theory and code is confirmed by comparing the axial radiation forces with the results obtained from references.

Acousto-optic study of the unusual cases of reflection of bulk elastic waves in a paratellurite crystal

The propagation and reflection of bulk ultrasonic waves in a paratellurite crystal have been investigated by the acousto-optic method. Simultaneous excitation of two acoustic waves by one piezoelectric transducer has been observed in a cell of complex, specially chosen configuration. Maximally efficient conversion of the energy of a quasi-longitudinal wave into a single reflected quasi-shear wave with a walkoff angle 72° is implemented for the reflection from a free crystal boundary. The wave beam compression by a factor of 7 is observed for this reflection. A reflection (close to backward) of waves with an angle of spatial separation of the incident and reflected beams equal to 8° is also implemented. The acousto-optic figure of merit values of the medium are calculated for arbitrary propagation and polarization directions of the interacting light and ultrasonic waves. Possible applications of the effects studied in acousto-optics and acoustoelectronics are indicated.

Interface effect on the electronic structure and optical properties of InAs/GaSb superlattices

The electronic structures of InAs/GaSb superlattices (SLs) are calculated in the framework of eight-band effective-mass theory, including the interface (IF) potential. With two adjustable parameters related to the types of two interfaces, the calculated energy gaps agree excellently with the experimental cut-off energy for a series of samples from different research groups, which proves the importance of IF effect, especially for the short-period SLs. Also, the optical properties of InAs/GaSb SLs are investigated. We proved that the intrinsic absorption coefficient of arbitrary polarization direction can be expressed as a function of and for symmetric-interface SL (D2d symmetry). The calculated agrees well with the experimental data. This method can be applied to predict the cut-off energy of InAs/GaSb SLs and design infrared detectors, and can also be applied to other SLs.