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Full wavefront control by photonic components requires that the spatial phase modulation on an incoming optical beam ranges from 0 to 2π. Because of their radiative coupling to the environment, all optical components are intrinsically non‐Hermitian systems, often described by reflection and transmission matrices with complex eigenfrequencies. Here, it is shown that parity or time symmetry breaking—either explicit or spontaneous—moves the position of zero singularities of the reflection or transmission matrices from the real axis to the upper part of the complex frequency plane. A universal 0 to 2π‐phase gradient of an output channel as a function of the real frequency excitation is thus realized whenever the discontinuity branch bridging a zero and a pole, that is, a pair of singularities, is crossing the real axis. This basic understanding is applied to engineer electromagnetic fields at interfaces, including, but not limited to, metasurfaces. Non‐Hermitian topological features associated with exceptional degeneracies or branch cut crossing are shown to play a surprisingly pivotal role in the design of resonant photonic systems. [ABSTRACT FROM AUTHOR]

Steel is one of the most widely used industrial materials in the world, and the classification of steel grades is of great concern in the steel industry. However, traditional analysis methods are time-consuming and complex, which are unsuitable for efficient detection. Gaussian beam-laser induced breakdown spectroscopy (LIBS) is widely used in steel analysis because of its speed and accuracy. However, the sample surface needs to be flat to keep the stability of LIBS, which limits the usage of LIBS. The Bessel beam, a non-diffraction beam with a long focal depth, has unique advantages in solving the variation of defocus caused by an uneven surface of the sample. To be suitable for industrial field inspection, a classification model for alloy steel samples based on a Bessel beam-LIBS system is established. In this study, the LIBS technology combined with a Bessel beam was used for the rapid detection and classification of steel samples with uneven surfaces. 510 LIBS spectra of 17 kinds of alloy steel based on a Gaussian beam and Bessel beam were collected separately, and based on the spectra, the recognition accuracies of alloy steel samples were compared between two systems. The spectra of uneven steel samples based on the Bessel beam-LIBS system can be definitely discriminated using support vector machines (SVMs), with an average accuracy of over 93.17%, which is better than that of the Gaussian beam. This research reflects the potential of Bessel beams in detecting samples with uneven surfaces and provides an effective method for industrial inspection. [ABSTRACT FROM AUTHOR]

In this manuscript, we analyzed the scattering of Laguerre–Gaussian (LG) beam by a perfect electromagnetic conductor (PEMC) sphere. The LG beam is famous due to an additional characteristic of orbital angular momentum (OAM). For an incident LG beam, the vector potential A LG p , l is employed to obtain the electromagnetic (EM) fields. LG beam may be described like superposition of Hermite–Gaussian (HG) modes, so the LG beam is expanded in the context of spherical vector wave functions (SVWFs) employing relation between LG and HG beam modes. The unknown scattering coefficients by an LG beam with helical phase profile are calculated using radial and tangential boundary conditions at the surface of PEMC sphere. The effects of the beam modes, beam width, and beam center coordinate position on the differential scattering cross section (DSCS) for a PEMC sphere have been computed. Numerical results explore that when the number of beam modes increase, the DSCS increases due to internal spatial degrees of freedom of the LG beam for nonzero p or l . This work has considerable potential to further investigate the aspects of metamaterials illuminated by LG beam for an optical community. [ABSTRACT FROM AUTHOR]

This article presents large deflection data for prismatic (unvarying cross section across length) and non-prismatic (tapered, i.e. varying cross section across length) cantilever beams subjected to concentrated tip loads using the finite element method for different taper ratios. The approximate nonlinear solution is derived from the perspective of a polynomial function. The tapered beams that correlate to the nonprismatic cantilever beams have different widths, depths, and diameters. Using the aforementioned large displacement data that have been analysed, a very simple approach is used to evaluate the large amplitude first mode frequency for the cantilever beam with (nonprismatic) tapered and without (prismatic) tapered. The current approach can be used effectively to find accurate results with far less computer capacity as compared to other methods available in the literature. The difference between the current findings and the bibliographic data is shown. The major goal of this work is to contribute to the simple description of polynomial functions for large amplitude first mode free vibration frequency problems with and without tapered beams in terms load parameter(𝜆) versus tip slope (𝛼)and tip amplitude(𝑎/𝐿). Large amplitude first mode frequency (𝛺) increases with tip slope(𝛼). This indicates that the prismatic and non-prismatic cantilever beams exhibit hardening type nonlinearity. At a particular tip slope(𝛼), the diameter taper shows higher frequency than other tapered beams and uniform beams. According to current studies, it can be restricted to a lower range of tip slope(𝛼)or amplitude(𝑎/𝐿). [ABSTRACT FROM AUTHOR]

In this paper, a simple design of an ultrathin and ultra‐broadband single‐layer MS based on double‐arrow‐shaped resonator (DASR) structure for both transmission and reflection modes in terahertz (THz) region is presented. The single‐layer MS is composed of a periodic array of the combination of the metal DASR and complementary circular patch (CCP) adhered on an ultrathin dielectric substrate. Numerical results show that the MS structure can convert CP wave to its orthogonal component after reflection and transmission simultaneously, and the corresponding amplitudes are ≈0.45 on average from 0.45 to 1.75 THz with a relative bandwidth of 118.2%, in which the CP conversion efficiency is closing to theoretical limit (25%) of the single‐layer structure. Furthermore, the 0–2π phase shifts for the reflected and transmitted orthogonal CP wave can be achieved simultaneously by adjusting the oriented angle (α) of the DASR structure along the wave propagation direction. For the concept proofs, wave beams deflection, vortex beam generation, and focusing effect for both reflection and transmission modes are demonstrated numerically. The design can provide new possibilities and potential to develop multifunctional full‐space devices. [ABSTRACT FROM AUTHOR]

Polarization plays a crucial role in light–matter interactions; hence its overall manipulation is an essential key to unlock the versatility of light manufacturing, especially in femtosecond laser direct writing. Existing polarization-shaping techniques, however, only focus on their manipulation in the transverse plane of light beams, i.e., two-dimensional control. In this paper, we propose a novel passive strategy that exploits a class of femtosecond laser written space varying birefringent elements to shape the polarization state along the optical path. As a demonstration, we generate a three-dimensional structured Bessel beam whose linear polarization state slowly evolves along the focus (typ. 90° within 60λ). Such a "helically polarized" Bessel beam allows imprinting "twisted nanogratings" in SiO2 glass which result in an extrinsic optical chirality at a micrometric scale and own a high optical rotation. Our work provides new perspectives for three-dimensional polarization manipulation and insights into applications in structured light, light–matter interaction, and chiral device fabrication. [ABSTRACT FROM AUTHOR]

Light sheet microscopy in live cells requires minimal excitation intensity and resolves three-dimensional (3D) information rapidly. Lattice light sheet microscopy (LLSM) works similarly but uses a lattice configuration of Bessel beams to generate a flatter, diffraction-limited z-axis sheet suitable for investigating subcellular compartments, with better tissue penetration. We developed a LLSM method for investigating cellular properties of tissue in situ. Neural structures provide an important target. Neurons are complex 3D structures, and signaling between cells and subcellular structures requires high resolution imaging. We developed an LLSM configuration based on the Janelia Research Campus design or in situ recording that allows simultaneous electrophysiological recording. We give examples of using LLSM to assess synaptic function in situ. In presynapses, evoked Ca2+ entry causes vesicle fusion and neurotransmitter release. We demonstrate the use of LLSM to measure stimulus-evoked localized presynaptic Ca2+ entry and track synaptic vesicle recycling. We also demonstrate the resolution of postsynaptic Ca2+ signaling in single synapses. A challenge in 3D imaging is the need to move the emission objective to maintain focus. We have developed an incoherent holographic lattice light-sheet (IHLLS) technique to replace the LLS tube lens with a dual diffractive lens to obtain 3D images of spatially incoherent light diffracted from an object as incoherent holograms. The 3D structure is reproduced within the scanned volume without moving the emission objective. This eliminates mechanical artifacts and improves temporal resolution. We focus on LLS and IHLLS applications and data obtained in neuroscience and emphasize increases in temporal and spatial resolution using these approaches. [ABSTRACT FROM AUTHOR]

The characteristics of high-power vortex Bessel beams in the terahertz range ( λ = 141 μm) obtained with the use of diffractive axicons (DAs) illuminated by a Gaussian beam of the Novosibirsk free-electron laser were studied. Two of the three possible types of DA recently described in our previous paper, namely, binary spiral silicon axicons (BAs), forming beams with a topological charge l equal to 0–4 and 9, and a diamond "holographic" axicon (HA), forming a beam with l = 9 , were used in the experiments. These axicons formed beams whose cross sections in the region of inner Bessel rings were close to those of ideal Bessel beams, but their intensities varied in azimuth with a frequency of l and 2 l for the BAs and HA, respectively. However, in the case of the BAs, the beams had a pronounced helical structure at the periphery, whereas for the HA, the beam was axisymmetric. By focusing these beams with a lens, we studied the structure of the so-called "perfect" beams (PBs). While an ideal Bessel beam exhibits a PB as a thin ring, in the case of the BAs, we observed a broadened ring structure consisting of 2 l short spirals, and for the HA, we observed a narrow ring with 2 l maxima in azimuth. A comparison of the numerical calculations and experiments showed that the observed azimuthal intensity variations can be attributed to inaccuracies in the preparation of the axicon relief and/or discrepancies between the calculated and actual wavelengths, within a few percent. The results of this work enable the establishment of quality requirements for axicon manufacture and the appropriate selection of the axicon type in accordance with the requirements for the beam. [ABSTRACT FROM AUTHOR]

The generation of an elliptical Bessel–Gauss beam has become a topic of interest in ultrafast laser processing of transparent materials because of its nearly non-diffractive elliptical central core. These beams can show potential in generating anisotropic structures down to the nanoscale and in producing asymmetries in the induced fields of thermo-mechanical constraints relevant for material structuring. However, maintaining the central core ellipticity is a challenge that requires further analysis, notably in the propagation behavior of phase anisotropies during the conical interference. This paper presents the controlled generation and propagation of a highly elliptical Bessel–Gauss beam using asymmetric phase-modulation technique. The study involves engineering different asymmetric phase holograms and analyzing their performances in terms of the non-diffractive property and uniformity of the generated beams. We indicate the presence in specific cases of diffraction and its influence on the invariance of the beam shape. The simulation results are in excellent agreement with the experimental results, which verifies the accuracy and reliability of our approach. [ABSTRACT FROM AUTHOR]

In this paper, the dynamic response of a Euler–Bernoulli beam subjected to transverse harmonic forces is calculated. The method of separation of variables combined with the mode shape superposition method, which includes the determination of eigenvalues, is used to define the velocity field of the beam surface. The Rayleigh integral was used to calculate the sound radiation and the beam was placed in an infinite baffle. Additional actuators are introduced in order to minimize the sound radiation, or, more specifically, the total sound power level of the vibrating beam, and their optimal position and force amplitude are determined; the conclusions were drawn from the optimization results. This paper proposes a method for faster determination of the optimal actuator parameters in order to achieve the minimum total sound power level. The validity of the obtained results is demonstrated with examples, whose solutions are compared to the results in the published literature. [ABSTRACT FROM AUTHOR]

This paper investigates nonlinear free and flexural analysis of hyperelastic beams. The constitutive relations of the hyperelastic beam were derived using the neo-Hookean strain energy function and Timoshenko beam theory. Also, the nonlinear governing equations and nonlinear natural boundary conditions were derived using Hamilton's principle. The meshless collocation method based on the multiquadric radial basis function (MQ-RBF) was utilized to discretize the nonlinear governing equations. Also, the arc-length algorithm was used to solve the nonlinear system of equations. To validate the results of the meshless method, different boundary conditions (clamped–clamped, simply supported–simply supported, clamped–simply supported, and clamped-free) were examined, and the results obtained from the meshless method were compared with those of the finite element method in Abaqus finite element software. The results show that the maximum and minimum differences between meshless and finite element methods occur in clamped and free-boundary conditions, respectively. The results also show that the meshless method based on the MQ-RBF has good accuracy compared to the finite element method for bending and free vibration analysis of hyperelastic beams. [ABSTRACT FROM AUTHOR]

This paper deals with a fully-dynamic piezoelectric beam model with a nonlinear force acting on the longitudinal displacements of the beam. The equations of motion follows a system of non-compactly coupled wave equation. As the magnetic effects are discarded by setting the magnetic permeability $ \mu $ to zero, the equations are fully decoupled to a single wave equation (electrostatic/quasi-static beam model). The existence of smooth finite-dimensional global attractors is proved by considering a damping injection to only one of the equations. Next, the existence of a finite set of determining functionals for the long-time behavior of the system is proved. Finally, to transition from the fully-dynamic beam model to the commonly-used electrostatic/quasi-static beam model, a singular limit problem $ \mu \to 0 $ is considered. This analysis allows to compare the attractors from one model to another in the sense of the upper semi-continuity of the attractor $ \mathcal{A}_{\mu} $ as $ \mu \to 0 $. [ABSTRACT FROM AUTHOR]

The beam with longitudinally varied polarization provides a new dimension for polarization applications, such as material processing, longitudinal depth detection, optical communications, etc. A few different methods have so far been investigated, including spatial light modulators and diffractive optical elements. However, these methods have complex optical path, large volume, which are difficult to integrate. Here, a birefringent dielectric metasurface is demonstrated, which is capable of generating Bessel beam whose polarization state continuously rotates along the propagation direction. According to the design, when a linearly polarized light illuminates on the metasurface, the outgoing light becomes linearly polarized zero‐order Bessel beam, whose polarization angle changes as the propagation distance increases. Experimental measurements are successfully carried out. Such scheme may open new doors for potential applications in depth perception, microscopic detection, and so on. [ABSTRACT FROM AUTHOR]

A method to construct the boundary shape function (BSF) and then two novel methods are developed to obtain the solutions of fourth-order singularly perturbed beam equation and nonlinear boundary value problem (BVP). In the first-type algorithm, the free function is a series of complete basis functions, while the corresponding BSFs are new bases. The trial functions with fractional powers exponential are suitable for the singularly perturbed beam equation under fixed-end and simply supported boundary conditions. With the aid of the BSF, we can improve the asymptotic and uniform approximations to exactly satisfy the prescribed boundary conditions. In the second-type algorithm, the solution of a nonlinear BVP is viewed as a boundary shape function, while the free function is regarded as a new variable. With this means, the fourth-order nonlinear BVP is exactly converted to an initial value problem with a new variable, the terminal value of which is unknown, when the initial conditions are given. The computed order of convergence and an error estimation are given. Numerical illustrations, including the singularly perturbed examples, show that the present methods, based on the new idea of the BSF, are highly effective, accurate, and fast convergent. [ABSTRACT FROM AUTHOR]

In this paper we discuss the motion of a beam in interaction with fluids. We allow the beam to move freely in all coordinate directions. We consider the case of a beam situated in between two different fluids as well as the case where the beam is attached only to one fluid. In both cases the fluid-domain is time changing. The fluid is governed by the incompressible Navier-Stokes equations. The beam is elastic and governed by a hyperbolic partial differential equation. In order to allow for large deformations the elastic potential of the beam is non-quadratic and naturally possesses a non-convex state space. We derive the existence of weak-solutions up to the point of a potential collision. [ABSTRACT FROM AUTHOR]

Long-distance, free space applications of orbital angular momentum (OAM) beams are limited by power loss and environmental turbulence. Although there have been many studies on the generation of high-power OAM beams, it is difficult to create a generated beam that is resistant to wander disturbance in low coherence conditions, let alone maintain the multiplexing of the OAM modes. In this work, we propose a partially coherent beam combining technology that enables generation of disturbance resistant and high-power OAM beams by controlling the spatial correlation of the light field with a partially coherent beam array. The OAM state of the generated beam can be transformed between single mode and multimode as designed. A multiplexed correlation vortex, which has low coherence and contains multiple spectral bands in OAM space, is produced experimentally. In a wander environment, the scintillation index and the relative power fluctuation of the multiplexed correlation vortex beam are reduced to 41% and 52% of those of completely coherent beams, respectively. These results represent a new methodology for OAM mode generation and show great potential for applications in complex environments. [ABSTRACT FROM AUTHOR]

In terms of research, the elliptical antenna arrays (EAA) synthesis is relatively novel. As it does not have to be circular in construction, this novel synthesis can maneuver the primary beam in the right direction, making it easier to realize. The amplitude and angular location of the ellipse, as well as the eccentricity of the ellipse, are all taken into account in the optimization process. The proposed hybrid algorithm is the SSWOA (Salp Swarm Whale Optimization Algorithm), which combines the Salp Swarm Optimization Algorithm (SSA) with the Whale Optimization Algorithm (WOA). The SSA algorithm serves as a guide, while the WOA algorithm serves as a helper in this method. We discover that optimization has a faster convergence time and high convergence accuracy when considering the benefits of SSA and WOA and applying them to the synthesis of antenna array layouts. If Griewank, Rosenbrock, Sphere, and Rastrigin test functions are used, it's worth noting that the hybrid method outperforms both WOA and SSA. [ABSTRACT FROM AUTHOR]

Interactions between collective multi-layered cells and an off-axis high-order Bessel beam (HOBB) are investigated. The generalized Lorenz-Mie theory is applied to derive the expansion of HOBB. Based on the additional theorem, multiple scattering of collective multi-layered nanoparticles is obtained by considering the tangential continuous boundary conditions. The present theory and codes are proven to be effective by comparing with the simulations obtained from the computer simulation technology (CST) software. Numerical results concerning the effects of beam order, beam conical angle, spherical layer number, core radius and outer layer radius, outer layer refractive index and the spherical number on the scattering of various types of aggregated multi-layered particles are displayed in detail, which may provide critical support for analytically understanding the optical scattering characteristics of aggregated multi-layered biological cells of complex shapes and may find important applications in manipulating multi-layered biological structures. [ABSTRACT FROM AUTHOR]

The deflection of Euler–Bernoulli beams under stochastic dynamic loading, exhibiting purely viscous behavior, is characterized by partial differential equations of the fourth order. This paper proposes a computational method to determine the approximate solution to such equations. The functions are approximated using two‐dimensional shifted Legendre polynomials. An operational matrix of integration and an operational matrix of stochastic integration are derived. The operational matrices assist in breaking down the problem under consideration into a set of algebraic equations that may be solved using any known numerical technique that leads to the solution of the stochastic beam equation. The well‐posedness of the problem is studied. The proposed methodology is demonstrated to be practical for addressing the novel stochastic dynamic loading problem by confirming the outcome using a few numerical examples. Thus the effectiveness and applicability of the technique are ensured. The solution quality is explored through diagrams. The accuracy of the method is substantiated by comparing it with the Runge–Kutta method of order 1.5 (R–K 1.5). The absolute error caused by the proposed technique is comparably much less than R–K 1.5. A simulation analysis is carried out with MATLAB, and an algorithm is developed. [ABSTRACT FROM AUTHOR]

Structured light fields, especially high-order Poincaré sphere (HOPS) beams, are attracting increasing attention for their intriguing properties and extensive applications. Here, we demonstrate a cascaded mode converter for generating HOPS beams of different orders. The cascaded mode converter is composed of q-plates and half waveplates, which realize switchable generation of HOPS beams of multiple different orders with reliable performance. Exponential growth of the available number of HOPS beams of different orders is achieved. The local polarization state and the order of the HOPS beams can be used as two degrees of freedom to encode 2 bits of information. The proposed method makes it possible to generate multiple and ultrahigh order Poincaré sphere beams and may have potential application in communication systems. [ABSTRACT FROM AUTHOR]

An analysis of electromagnetic scattering by perfect electromagnetic conductor (PEMC) sphere using Bessel beam incidence is presented which is based on the generalized Lorenz–Mie theory (GLMT). The PEMC is famous for the generalization of the renowned concept of perfect electric and perfect magnetic conductor (PEC and PMC). The scattering problem is solved by representing the Bessel beam fields i.e., incident and scattered in the context of vector spherical wave functions (VSWFs). The unknown expansion field coefficients can be found out by solving linear equations which are attained from the implementation of boundary conditions (BCs) of PEMC sphere. Computations of the scattering cross-section C sca and the extinction cross-section C ext are performed. The impact on scattering and extinction cross-section for admittance parameter, conical angle, and sphere size parameter are analyzed. Considering a special case for conical angle i.e., α = 0 ∘ , the numerical results of scattering cross-section for Bessel beam and plane wave are same. [ABSTRACT FROM AUTHOR]

Electron vortex beams (EVBs, also known as twisted electron beams) possess an intrinsic orbital angular momentum (OAM) with respect to their propagation direction. This intrinsic OAM represents a new degree of freedom that provides new insights into investigating the dynamics of electron impact ionization. In this communication, we present, in the first Born approximation (FBA), the angular profiles of the triple differential cross section (TDCS) for the (e, 2e) process on CH 4 and NH 3 molecular targets in the coplanar asymmetric geometry. We compare the TDCS of the EVB for different values of OAM number m with that of the plane wave. For a more realistic scenario, we investigate the average TDCS for macroscopic targets to explore the influence of the opening angle θ p of the twisted electron beam on the TDCS. In addition, we also present the TDCS for the coherent superposition of two EVBs. The results demonstrate that the twisted (e, 2e) process retrieves the p-type character of the molecular orbitals, which is absent in the plane wave TDCS for the given kinematics. The results for the coherent superposition of two Bessel beams show the sensitivity of TDCS toward the OAM number m. [ABSTRACT FROM AUTHOR]

Increasing the depth of field (DOF) is a crucial issue for imaging through scattering media. In this paper, an improved genetic algorithm is used to modulate the wavefront of light through scattering media, by which high-quality refocusing and imaging through scattering media are achieved. Then, the DOF of the imaging system is effectively extended by further modulating the refocused beam into a non-diffraction beam. Two kinds of non-diffraction beams, i.e., a Bessel beam and Airy beam, were produced as a demonstration. The experimental results show that compared to the Gaussian beam, the DOF of the imaging system by combining the wavefront shaping and non-diffraction Bessel beam or Airy beam can be improved by a factor of 1.1 or 1.5, respectively. The proposed method is helpful for the technical development of high-quality imaging through scattering media with a large DOF. [ABSTRACT FROM AUTHOR]

We obtain a transform that relates the standard Bessel–Gaussian (BG) beams with BG beams described by the Bessel function of a half-integer order and quadratic radial dependence in the argument. We also study square vortex BG beams, described by the square of the Bessel function, and the products of two vortex BG beams (double-BG beams), described by a product of two different integer-order Bessel functions. To describe the propagation of these beams in free space, we derive expressions as series of products of three Bessel functions. In addition, a vortex-free power-function BG beam of the mth order is obtained, which upon propagation in free space becomes a finite superposition of similar vortex-free power-function BG beams of the orders from 0 to m. Extending the set of finite-energy vortex beams with an orbital angular momentum is useful in searching for stable light beams for probing the turbulent atmosphere and for wireless optical communications. Such beams can be used in micromachines for controlling the movements of particles simultaneously along several light rings. [ABSTRACT FROM AUTHOR]

To form a diffraction-free beam with a complex structure, we propose to use a set of primitives calculated iteratively for the ring spatial spectrum. We also optimized the complex transmission function of the diffractive optical elements (DOEs), which form some primitive diffraction-free distributions (for example, a square or/and a triangle). The superposition of such DOEs supplemented with deflecting phases (a multi-order optical element) provides to generate a diffraction-free beam with a more complex transverse intensity distribution corresponding to the composition of these primitives. The proposed approach has two advantages. The first is the rapid (for the first few iterations) achievements of an acceptable error in the calculation of an optical element that forms a primitive distribution compared to a complex one. The second advantage is the convenience of reconfiguration. Since a complex distribution is assembled from primitive parts, it can be reconfigured quickly or dynamically by using a spatial light modulator (SLM) by moving and rotating these components. Numerical results were confirmed experimentally. [ABSTRACT FROM AUTHOR]

We propose a compact method to experimentally synthesize a class of vector beam arrays with periodic higher-order Poincaré sphere (HOPS) polarization states by engineering the spatial coherence structure of a partially coherent light source. We demonstrate that the spatial coherence structure and polarization state of the partially coherent source can be simultaneously controlled using a phase-only spatial light modulator and a common-path interferometric arrangement with the aid of a complex-random-mode representation method. We show experimentally that the polarization state of a single HOPS beam in the source plane can be mapped into a beam array generated in the far field, and the degree of polarization of the beam array can be conveniently controlled with spatial coherence engineering. Our method provides an alternative way to synthesize beam arrays with structured coherence and polarization properties. [ABSTRACT FROM AUTHOR]

Cone-beam computed tomography (CBCT) produces high-resolution of hard tissue even in small voxel size, but the process is associated with radiation exposure and poor soft tissue imaging. Thus, we synthesized a CBCT image from the magnetic resonance imaging (MRI), using deep learning and to assess its clinical accuracy. We collected patients who underwent both CBCT and MRI simultaneously in our institution (Seoul). MRI data were registered with CBCT data, and both data were prepared into 512 slices of axial, sagittal, and coronal sections. A deep learning-based synthesis model was trained and the output data were evaluated by comparing the original and synthetic CBCT (syCBCT). According to expert evaluation, syCBCT images showed better performance in terms of artifacts and noise criteria but had poor resolution compared to the original CBCT images. In syCBCT, hard tissue showed better clarity with significantly different MAE and SSIM. This study result would be a basis for replacing CBCT with non-radiation imaging that would be helpful for patients planning to undergo both MRI and CBCT. [ABSTRACT FROM AUTHOR]

Terahertz technology and vortex beams have demonstrated powerful capabilities in enhancing the channel capacity of communication systems. This work proposes a design strategy of dual-band and dual-function 3-bit coding metasurface based on beam polarization characteristics. The unit cell of the metasurface is composed of two pattern structures, which has the ability to flexibly and independently control the reflection phases of incident plane wave at two frequency bands. The metasurface designed in this work is a combination of two patterns according to the addition operation and the convolution operation. The 3-bit coding metasurface generates two orbital angular momentum (OAM) beams with a deflection of 12.1° with modes l 1 = + 1 and l 2 = − 1 under the y-polarized incidence at 0.6 THz. Similarly, the designed metasurface produces two OAM beams with a deflection of 16.5° under the incidence of x-polarized wave at 0.9 THz, and the modes are l 3 = + 1 and l 4 = − 2 . The full-wave simulation results agree well with the theoretical predictions, which could prove the correctness and effectiveness of the proposed method. The metasurface designed according to this method has potential applications in multiple-input multiple-output (MIMO) communication systems. [ABSTRACT FROM AUTHOR]

In this paper, the flexural vibration of uniform and non-uniform rotating shafts based on the Timoshenko beam theory is investigated. Considering shear deformation and gyroscopic effects to build an exact framework of a solution, the fourthorder differential equation of vibration is solved by an analytical method. The overall transfer matrix of the system formed by a series of flexible distributed in addition to lumped elements is achieved. The results obtained by the distributed lumped modeling technique (DLMT) are verified with other techniques. The damped frequencies obtained by the hybrid modeling method for a multistep gas turbine rotor system using the Euler-Bernoulli and Timoshenko beam theories are compared with the results of the transfer matrix method (TMM). It is shown that the presented method provides highly accurate results, while with no compromise, it can be simply and effectively employed for complex systems. It is also shown how the Hooke and Jeeves and the ant colony optimization (ACO) besides the direct enumeration method can be applied to obtain the damped natural frequencies of complicated vibrational systems such as the gas turbine rotors. The comparison between the frequency and damping ratio values obtained by the optimization and direct enumeration methods shows less than 1% error for different cases. [ABSTRACT FROM AUTHOR]

We describe the construction of an optical-space, cylindrical black hole induced by high pressure in a dense fluid. Using an approximate analogy between curved spacetime and optics in moving dielectric media, we derive the mass of the black hole thus created. We describe the resulting optical-space using a Bessel beam profile and Snell's law to understand how total internal reflection produces a cylindrical, optic black hole. [ABSTRACT FROM AUTHOR]

Fabrication of a through hole in a polyimide film (PI) was demonstrated by holographic ultraviolet (UV) nanosecond laser processing with a computer-generated hologram displayed on a phase-only spatial light modulator (SLM). The UV laser was directly modulated into a Bessel beam by a diffractive axicon displayed on the SLM. The direct modulation contributed to improved light-utilization efficiency of the UV laser and a simplified optical setup compared to the conventional method based on a combination of an SLM and harmonic generation using a nonlinear optical crystal. The Bessel beam reduced the number of pulse shots required for through-hole fabrication to 1/5 compared to the Gaussian beam near the ablation threshold energy of the PI film. Furthermore, adaptive optics was implemented in holographic laser processing to compensate for aberrations in the optical setup. The aberration was reduced to 1/5 compared with before the compensation. The proposed method is suitable for improving the throughput and accuracy of drilling, cutting, and additive manufacturing using UV lasers with industrial requirements. [ABSTRACT FROM AUTHOR]

The expressions of the axial and transverse acoustic radiation forces of a rigid sphere arbitrarily positioned in a zero-order Mathieu beam are derived in this paper. The expansion coefficients of the off-axis zero-order Mathieu beam are obtained using the addition theorem of the Bessel functions, and numerical experiments are conducted to verify the theory. The three-dimensional acoustic radiation forces on a rigid sphere are studied when the beam is set at different ellipticity parameters, half-cone angles, and offsets of the incident wave relative to the particle center. Simulation results show that the axial acoustic radiation forces of the rigid sphere are always positive, but the transverse forces vary with the positions of the particle and the beam parameters. Also, by changing the frequency, half-cone angle, and offset of the zero-order Mathieu beam, the value and direction of the transverse forces can be adjusted, which has applications in controlling the rigid sphere to be close to or away from the beam axis. Furthermore, the finite element model is set up to verify the theoretical model, and the results obtained by the two methods are in good agreement. This work may contribute to a better understanding of the underlying mechanisms of the particle manipulation with different acoustic beams. [ABSTRACT FROM AUTHOR]

Enhancing the infrared window transmittance of zinc sulfide (ZnS) is important to improve the performance of infrared detector systems. In this work, a new hybrid micro/nanostructure was fabricated by an optimal Bessel femtosecond laser on ZnS substrate. The surface morphologies and profiles of ASS ablated by a 20× microscope objective Bessel beam are described, indicating that the nanoripples on the micropore were formed by the SPP interference and the SPP scattering in a particular direction. Further, the maximum average transmittance of ASS increased by 9.7% and 12.3% in the wavelength ranges of 5~12 μm and 8~12 μm, respectively. Finally, the antireflective mechanism of the hybrid micro/nanostructure is explored using the novel electromagnetic field model based on the FDTD method, and we attribute the stable antireflective performance of ASS in broadband to the interface effective dielectric effect and LLFE. [ABSTRACT FROM AUTHOR]

This work presents a 12-element 360° azimuth plane scanning planar circular antenna array for compact THz wireless devices. Proposed array comprises of 12 bow-tie Yagi-Uda directional antennas, operating within 0.235–0.322 THz band where each antenna achieves a maximum radiation beam for an angle of around 30°, arranged in a circular fashion to cover 360°. Individual antennas are stamped on a silicon dioxide (SiO2) dielectric substrate having compact dimensions of 1.35 mm × 1 mm × 0.06 mm and employ gold material of thickness 5 µm as a conducting material in the top and bottom planes. Maximum peak gain of each antenna is found to be 10.4 dBi at 0.322 THz within the operating band. Three parasitic elements are employed as directors to enhance the directional properties. Initially, a single element bow-tie Yagi-Uda antenna design is presented and then followed by a 6-element and 12-element circular antenna array design. Exhibiting compact dimensions, higher directivity, better performance and simple design lead to a suitable module for smart THz wireless scanning devices in the range of IEEE 802.15.3d (0.252–0.325 THz) standard and H-band (0.22–0.32 THz). [ABSTRACT FROM AUTHOR]

This paper considers the analysis of slender single‐sided transversely cracked beams with a linear variation of width where transverse displacements can occur exclusively due to axial tensile forces. The simplified model where the crack is represented through an internal hinge endowed with a rotational spring that takes into account the cracked cross section's residual stiffness has already established itself as a decent alternative to the detailed 2D or 3D finite element, offering a good ratio between the accuracy of its results against the computational efforts required. The first stage of the presented research proved that the solutions of the bending governing differential equations with directly included axial tensile force are not required. However, the need for enhancement of the model's governing parameters clearly emerged. Thus, the definitions of the moment lever arm and rotational spring stiffness were studied and fittingly updated. In the last stage, the modelling of the considered phenomenon by a newly derived one‐dimensional beam finite element with closed‐forms of the element's stiffness matrix and load vector was executed. At the end of the study, the performance and the quality of the newly obtained solutions were verified through several comparative case studies that complement the derivations. [ABSTRACT FROM AUTHOR]

In this study, the post-buckling behavior of a transverse functionally graded beam is investigated. Euler–Bernoulli beam theory (EBT) and shear deformable beam theories are taken into account in deriving the mathematical models of the beam using the vector approach. Timoshenko theory (TBT) and six different higher order beam theories (HOBT), namely Reddy, Touratier, Soldatos, Karma, Akavcı and Violet, are considered as shear deformable beam theories. It has been shown that mathematical models of shear deformable beam theories can be obtained using the vector approach. There are two different models developed for shear deformable beam theories depending on normal and shear forces and moment. It is found that the model which is named as Model 2 in this study yield inappropriate results. The functionally graded materials are characterized by using power law functions. The non-dimensional integro-non-linear differential equations system is solved analytically. The critical load values calculated for EBT, TBT and HOBT theories depending on different material conditions and slenderness ratio values are presented in tables. In addition, pitchfork bifurcation diagrams are drawn showing the post-buckling behavior of the beam. In addition, the regions where the examined beam theories are valid depending on the slenderness coefficient are shown. [ABSTRACT FROM AUTHOR]

In this paper, a novel design of superlens based on photonic bandgap structure for high resolution point spread function (PSF) is reported at a wavelength of 3 μm. The lens is able to generate a non-diffraction Bessel beam with a number of focusing points with variant resolution limits. The optimized structure provides high resolution in both lateral and axial directions. The maximum achieved lateral resolution of PSF is down to ~ 0.27λ with corresponding axial resolution down to ~ 0.57λ attaining a FOM, the inverse of the product of both resolution limits, of ~ 6.49. Meanwhile, the maximum axial resolution is down to ~ 0.4λ with corresponding lateral resolution down to ~ 0.33λ with a FOM of ~ 7.34. In addition, the proposed design is able to generate a focusing point extended in space up to ~ 0.98 µm with a sub-diffraction lateral resolution down to ~ 0.47λ. Furthermore, the reported superlens demonstrates a sub-diffraction focusing in lateral direction along the range the bandgap wavelengths (from 2.4 to 3.6 µm) showing a significant increase of focal depth when decreasing the operating wavelength. Remarkably, a high focal depth up to ~ 1.77 µm is achieved at the operating wavelength of 2.6 µm. The suggested design has a tremendous potential in 3D biological imaging and biosensing applications. [ABSTRACT FROM AUTHOR]

In this work, we fabricated the antireflection microstructures (ARMs) on ZnSe surfaces using a femtosecond Bessel direct laser writing in burst mode. The morphology and transmittance performance of ARMs with different single-pulse energies (from 200 nJ to 500 nJ), different burst modes (burst 1, 3, and 5 modes), different periods (from 3 μm to 6 μm), and different arrangements were investigated. The results revealed that tetragonally arranged ARMs fabricated by 500 nJ of single-pulse energy, the burst 3 mode, and a period of 3 μm show the best transmittance performance. The average transmittance of the ARMs was about 17.13% higher than that of bulk ZnSe in the range of 8–12 μm, and the highest transmittance of 81.75% (an improvement of 18.63% on one side of the ZnSe) was achieved at 12.36 μm. This process makes it possible to enhance ARMs' transmittance in the infrared wavelength range by using direct laser writing in burst mode. [ABSTRACT FROM AUTHOR]

We report on an optical setup to generate multi-Bessel beam profiles combining a refractive axicon and a spatial light modulator. Based on their particular beam profile, Bessel beams offer advantageous properties for micro drilling processes and internal volume processing, especially for transparent materials. In addition, the laser power of industrial, ultrashort pulsed lasers has increased significantly over the last few years, offering the possibility for highly efficient processes using multi-spot profiles. Our optical concept combines the dynamic possibilities of beam splitting using a spatial light modulator with the benefits of Bessel beams, which facilitates multi-Bessel beam processing. Beside the simulation and experimental evaluation of the generated multi-Bessel beams, we exemplify the applicability of the developed module for the perforation of thin metal foils by micro drilling. [ABSTRACT FROM AUTHOR]

A flexible beam is recognized as a lightweight structure that is prone to excessive vibration, resulting in poor performance. Thus, controlling unwanted vibration is necessary to maintain the system's performance. Therefore, this study presents a technique to suppress undesired vibration in a flexible beam structure by introducing active vibration control (AVC). However, to develop an effective controller, an appropriate flexible beam model must first be obtained. In recent times, one of the best methods employed to model a flexible beam structure is system identification via a swarm intelligence algorithm. In this study, an intelligent algorithm acknowledged as cuckoo search (CS) was acquainted. The capability of the proposed algorithm was verified using three robustness techniques which were correlation test, pole-zero diagrams and mean square error (MSE). The simulation result showed that the CS algorithm achieved superior performance by achieving the lowest MSE of 6.1547x10-9, a correlation test between a 95% confidence level and high stability. Next, a proportionalintegral-derivative (PID) controller tuned by the Ziegler-Nichols method was developed using the transfer function accomplished from the CS model. Two types of interference, namely single and multiple sine waves were introduced to validate the effectiveness of the controller. The controller successfully achieved a 30.2 dB of attenuation level for both disturbances. [ABSTRACT FROM AUTHOR]

Dicing is a critical step in the manufacturing process for the application of sapphire. In this work, the dependence of sapphire dicing on crystal orientation using picosecond Bessel laser beam drilling combined with mechanical cleavage was studied. By using the above method, linear cleaving with on debris and zero tapers was realized for the A1, A2, C1, C2, and M1 orientations, except for the M2 orientation. The experimental results indicated that characteristics of Bessel beam-drilled microholes, fracture loads, and fracture sections of sapphire sheets were strongly dependent on crystal orientation. No cracks were generated around the micro holes when laser scanned along the A2 and M2 orientations, and the corresponding average fracture loads were large, 12.18 N and 13.57 N, respectively. While along the A1, C1, C2, and M1 orientations, laser-induced cracks extended along the laser scanning direction, resulting in a significant reduction in fracture load. Furthermore, the fracture surfaces were relatively uniform for A1, C1, and C2 orientations but uneven for A2 and M1 orientations, with a surface roughness of about 1120 nm. In addition, curvilinear dicing without debris or taper was achieved to demonstrate the feasibility of Bessel beams. [ABSTRACT FROM AUTHOR]

Integrating multiple independent functions into a single optical component is one of the most important topics in research on photoelectric systems. In this paper, we propose a multifunctional all-dielectric metasurface that can achieve a variety of non-diffractive beams depending on the polarization state of the incident light. Using the anisotropic TiO2 rectangular column as the unit structure, the three functions of generating polygonal Bessel vortex beams under left-handed circularly polarized incidence, Airy vortex beams under right-handed circularly polarized incidence and polygonal Airy vortex-like beams under linearly polarized incidence are realized. In addition, the number of polygonal beam sides and the position of focal plane can be adjusted. The device could facilitate further developments in scaling complex integrated optical systems and fabricating efficient multifunctional components. [ABSTRACT FROM AUTHOR]

Periodic nanohole arrangements constitute an important building block of advanced photonic devices. Aside from standard nanofabrication tools, a direct laser‐based approach is introduced here, that enables single‐step and point‐by‐point machining of arrays of holes with subwavelength diameters and depths reaching several micrometers at the surface of fused silica. The method relies on a simple optical arrangement including an axicon combined with an amplitude mask to shape the laser intensity in appropriately truncated micro‐Bessel beams of adjustable length. The suitability and limitations of the technique are investigated to fabricate arrays of cylindrical nanoholes with tunable depths. In particular, the challenge of avoiding crosstalk effects during the laser‐writing process of high‐density arrays is explored. The achievability of square arrays of nanoholes at the surface of fused silica, with diameters down to 200 nm and variable depths from 3 to 20 µm at a spatial density defined by a pitch of 1.5 µm is demonstrated. The performance level shows the potential of the direct‐laser‐processing method towards the realization of integrated devices, offering a highly flexible and cost‐effective alternative technique to current nanofabrication methods. [ABSTRACT FROM AUTHOR]

This article outlines the use of Fredholm integral equations (also known as Fredholm transformation approach) for free vibration analysis of non-uniform and stepped axially functionally graded (AFG) beams. The method is shown to be capable of dealing with beams of arbitrary variations of both cross section dimensions and material properties. Tabulated results of free vibration analysis for beams with various classical boundary conditions are presented. The governing equation with varying coefficients is transformed to Fredholm integral equations. Natural frequencies can be determined by requiring that the resulting Fredholm integral equation has a non-trivial solution. Our method has fast convergence, and obtained numerical results have high accuracy. Effects of axial force and shear deformation are investigated on the natural frequencies of AFG beams. The accuracy of obtained results is verified with those obtained in other available references. The present results are of benefit to optimum design of non-homogeneous tapered beam structures and graded beams of special polynomial non-homogeneity. [ABSTRACT FROM AUTHOR]

The number of mirror segments, mirror geometry and orientation are essential parameters when assessing the beam-shaping capabilities of deformable mirrors. Here, we use a Liquid Crystal on Silicon Spatial Light Modulator (LCoS-SLM) to mimic the mechanical design of a deformable mirror and quantitatively analyse the effect of the number of mirror segments and their geometrical structure on resulting structured modes. Our approach can be used as a test bed prior to designing a deformable mirror for high power beam shaping. [ABSTRACT FROM AUTHOR]

Coherent anti-Stokes Raman scattering (CARS) spectroscopy plays an important role in chemical analysis for transient flow dynamics. Due to the turbulent ambient conditions, the CARS spectrum often suffers from a poor signal-to-noise ratio (SNR) and cannot provide a convincing measurement. Here, we report on a CARS spectroscopic method using a Bessel beam to enhance the spectral fidelity and SNR in a quasi-turbulent environment. Compared with traditional CARS, the measurement accuracy is significantly improved by taking advantage of the anti-scattering and self-healing characteristics of the Bessel beam. Our preliminary results indicate that Bessel beam CARS could be a promising method for high precision turbulent flow measurement fields. Graphical Abstract [ABSTRACT FROM AUTHOR]

Determination of polarization states of electromagnetic waves plays a crucial role in photonic applications. However, it is very challenging to determine the polarization state of continuous terahertz (THz) waves. Here, a metasurface‐like metallic waveguide array (MWA) is proposed to address this by measuring both the phase difference and amplitude ratio of its two orthogonal components based on generation and interference of polarization‐multiplexing vortex beams. When a full‐polarized THz wave passes through the MWA, its two orthogonal components will be converted into +1st‐ and −1st‐order Bessel vortex beams, respectively. Their projection components in a proper polarized direction can interfere with each other, and their initial phase difference can be measured in real‐time owing to its linear relationship with the azimuth of the dark fringe in interference patterns. The two Bessel beams can be further collected separately using a linear polarizer to obtain their amplitude ratio. Therefore, the polarization state of incident waves can be determined with both the phase difference and amplitude ratio. The proposed method enables a convenient polarization determination of continuous THz waves and has great potential for developing polarization‐dependent investigations and applications in THz detection, communication, and sensing. [ABSTRACT FROM AUTHOR]

This paper proposes a synthesis and optimization procedure to generate user-specific shaped and multiple beams in any arbitrary 3D space. The synthesis method generates independently controllable multiple beams over different azimuth and elevation angles with variable peak powers. These multiple beams can form any user-defined shaped pattern with an optimum number of beams, their power, and placement in the θ , ϕ angles using the proposed direct synthesis method. Different evolutionary algorithms are employed to optimize the beam peak parameters to mitigate the ripple, side lobe level, and beam spread. The synthesis method is validated on a fully functional integrated 5G mmWave phased array for various shaped beam patterns. Measured sector, isoflex beams between θ = ± 40 ∘ , c s c 2 , and dual beams with unequal powers are presented and compared with the shaped beam synthesis method. [ABSTRACT FROM AUTHOR]