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The improved absolute nodal coordinate formulation (D-H-ANCF) is proposed for analyzing dynamic behaviors of the variable cross-section beam with large aspect ratio. The higher-order ANCF (H-ANCF) is established by introducing higher-order freedom degrees. Then the reduction factors of each element are proposed by considering the aspect ratio criterion and shear performance criterion. The experiments are studied to verify the correctness of the proposed method. In conclusion, shear locking can be solved by D-H-ANCF. And the deformation and cross-section distortion also can be accurately predicted by D-H-ANCF. Moreover, the computing efficiency of D-H-ANCF can be improved by introducing reduction factors. [ABSTRACT FROM AUTHOR]

Based on the existing permanent load equilibrium method, influence matrix method and adaptive control method, a distributed algorithm and control method for the cable forces of hybrid laminated girder cable-stayed bridges is proposed. The method uses the permanent load equilibrium approach to initially determine the permanent load cable forces, then adjusts it based on the influence matrix of the main girder displacement, and finally combines the calculation of finite element software to determine the cable forces that satisfy the internal force requirements of each member of the hybrid laminated girder cable-stayed bridge under the joint action of permanent load and live load. Through adjusting the cable force of an actual bridge, it can be found that this method is highly efficient in calculation, and the efficiency and accuracy of control of the cable forces are high, ensuring that the cable forces and alignment of the bridge structure after completion are in line with the design expectations. [ABSTRACT FROM AUTHOR]

A theory for the characterization of the fourth-order moment of electromagnetic wave beams is presented in the case when the source is partially coherent. A Gaussian–Schell model is used for the partially coherent random source. The white-noise paraxial regime is considered, which holds when the wavelength is much smaller than the correlation radius of the source, the beam radius of the source, and the correlation length of the medium, which are themselves much smaller than the propagation distance. The complex wave amplitude field can then be described by the Itô-Schrödinger equation. This equation gives closed evolution equations for the wave field moments at all orders and here the fourth-order moment equations are considered. The general fourth-order moment equations are solved explicitly in the scintillation regime (when the correlation radius of the source is of the same order as the correlation radius of the medium, but the beam radius is much larger) and the result gives a characterization of the intensity covariance function. The form of the intensity covariance function derives from the solution of the transport equation for the Wigner distribution associated with the second-order wave moment. The fourth-order moment results for polarized waves are used in an application for imaging of partially coherent sources. [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]

The nonlinear behavior of thin-walled, sinusoidal, slightly curved beams with pinned ends under lateral sinusoidal loading is considered numerically, based on Eringen's nonlocal elasticity theory and the Euler-Bernoulli beam theory. Geometrically nonlinear governing differential equations are solved by using the finite difference method and the displacement-controlled Newton-Raphson method. The influences of the nonlocal parameter, the initial curvature, and the span of the slightly curved beam on the buckling values are examined. Unlike the relevant previous studies, it is stated in this study that the values of these parameters must remain within certain limits in order to have purely snap-through buckling behavior. Moreover; the graphs of the deformed shapes of the slightly curved beams, the internal forces and the horizontal support reactions corresponding to the various phases of the equilibrium paths (including the prebuckling, buckling and postbuckling stages) are drawn for various values of the nonlocal parameter and the effect of the nonlocal parameter on these graphs are investigated in detail. The study contains insightful results and concluding remarks improving the comprehension of the snap-through phenomenon of the slightly curved beams under lateral loading. [ABSTRACT FROM AUTHOR]

The properties of a linearly polarized cosine-hyperbolic-Gaussian beam (ChGB) propagating in a chiral medium are investigated theoretically by using the Huygens-Fresnel diffraction integral. Beam intensity distribution characteristics in the chiral medium are discussed with numerical examples. The linearly polarized ChGB is found to split into a superposition of left and right circularly polarized Gaussian components, and its intensity pattern exhibits a variable shape depending on the chirality factor and decentered parameter b. The output beam can exhibit a richer intensity pattern compared to the Gaussian beam. The results could be beneficial for the application of ChGB in beam shaping and optical micromanipulation. [ABSTRACT FROM AUTHOR]

The propagation properties of a circular cosh-Gaussian beam (CiChGB) in a fractional Fourier transform (FRFT) optical system are investigated theoretically. The analytical expressions for a CiChGB propagating through apertured and unapertured FRFT systems are derived based on the Collins formula and the expansion of the hard-aperture function into a finite sum of Gaussian functions. From the obtained expressions, the evolution of the intensity distribution at the output plane is analysed with illustrative numerical examples. It is shown that the intensity distribution of the CiChGB propagating in FRFT is closely dependent on the decentred beam parameter and the aperture size besides the fractional order of the FRFT system. The results obtained may be beneficial to applications in laser beam shaping, optical trapping, and micro-particle manipulation. [ABSTRACT FROM AUTHOR]

Due to their unlimited shelf life, high impact resistance, recyclability, and fast processing time, the use of carbon fibers in combination with a thermoplastic matrix promises a fiber metal laminate (FML) with improved properties and potentially automated series production. Accordingly, the formability and performance of fast forming technologies, i.e., the hot stamping of thermoplastic FMLs, are increasingly attracting research interest. In this study, a new one-step hot stamping process is first proposed to produce curved thermoplastic FML beams fabricated by Al sheets, PEEK films, and CF/PEEK prepregs (Al/CF/PEEK). Then, the effects of the forming temperature and punching speed on the formability, as well as on the performances of the curved beams, i.e., their macro- and micro-defects, interlaminate strength and failure, thickness distribution, and spring-back, are experimentally investigated via SEM observations, four-point bending tests, and digital image correlations. It is found that curved Al/CF/PEEK laminate beams with the least spring-back (<0.2°) and thickness reduction (<0.2 mm), the fewest defects, the highest curved beam strength (195 N·mm/mm), and the highest interlaminate strength (16.5 MPa) can be produced under the forming temperature of 380°C and punching speed of 10 mm/s. [ABSTRACT FROM AUTHOR]

This work investigates the problem of optimal placement and geometry of piezoelectric sensors and actuators (S/A) to improve active vibration control performance of smart laminated beam. Theoretical formulation is based on efficient layer-wise finite element model along with an optimal control theory. Control theory is implemented in state space format considering a reduced order model. A laminated beam with collocated piezoelectric S/A placed at the top and bottom surfaces has been considered. A series of simulation based on Taguchi design of experiment has been carried out to determine the optimal placement and geometry of the S/A to achieve best control performance that is maximum modal active damping ratio ξ /minimum settling time with minimum actuator voltage. A multi-criteria optimisation has been performed using Proximity Indexed Value (PIV) integrated with entropy methods. Further, the analysis of mean (ANOM) and analysis of variance (ANOVA) are performed to identify the most significant input parameter based on their percentage contribution. For the smart cantilever beam considered in the analysis, the location of the S/A is the most significant having maximum percentage contribution (35.69%) followed by its length (33.04%) and thickness (24.55%). [ABSTRACT FROM AUTHOR]

This paper provides an analytic method to study propagation characteristics of a linearly polarized Bessel vortex beam through a homogeneous magnetized plasma slab. The incident Bessel vortex beam, as well as the reflected, transmitted and internal fields are expanded in terms of cylindrical vector wave functions (CVWFs). The effects of plasma thickness, electron density and magnetic induction strength on the contour profiles of the reflected and transmitted beams and orbital angular momentum (OAM) spectra are analyzed and discussed in detail. In particular, the magnetic induction strength has a significant impact on the polarization of the transmitted beam, but not on OAM state distribution. The channel capacity of THz OAM multiplexing decreases with an increase of plasma thickness and electron density. [ABSTRACT FROM AUTHOR]

Compared with traditional vortex beams, high-order Bessel beams (HoBBs) have the unique characteristics of non-diffraction and self-healing, which makes them more competitive in fields of complex-environment optical manipulation and long-distance optical communication. With the progress of machining technology, the realization of micro-nano-sized optical components becomes possible, and integrated optics becomes the trend of future development. However, up to now, the traditional devices for generating HoBBs have a large volume and high weight, which makes it difficult to achieve optical integration. Here, we have designed an ultra-compact micro-optical element to generate high-quality micro-sized HoBBs. Good morphology of the element prepared via laser direct writing (LDW), and beam characteristics of non-diffraction and self-healing were demonstrated experimentally. [ABSTRACT FROM AUTHOR]

First, we study the space-dicretized Finite Difference approximations of the system of non-compactly coupled partial differential equations (PDE) model of piezoelectric beam equations involving magnetic effects. The system strongly couples longitudinal vibrations strongly with the electromagnetic effects due to the Maxwell's equations. Even though the system is known to be exactly observable with two boundary observations, one mechanical and one electrical, its approximations do not retain uniform exact observability with respect to the mesh parameter h → 0. This is mainly due to the loss of the uniform gap among two branches of eigenvalues. To obtain a uniform gap, and therefore, a uniform observability result with respect to mesh parameter, a direct filtering method is adopted to eliminate artificial high-frequency eigenvalues of the approximated model. In fact, as the mesh parameter goes to zero. Both the discrete multipliers and the non-harmonic Fourier series are utilized for proving main results. The main hurdle in proving the discrete energy estimates for the two strongly coupled wave equations is non-identical wave speeds and con-compact coupling of the wave system. [ABSTRACT FROM AUTHOR]

Wide-angle X-ray scattering (WAXS) is routinely used to characterize the ordered structure in materials. The measured angles are generally calibrated by using standard samples with several diffraction peaks. When a WAXS instrument uses a one-dimensional linear detector, which is tilted to the direct beam, the angle calibrations need three standard diffraction peaks. This contribution presents the corresponding analytical solution of the calibration equations and error estimation matrix and performs error simulation and experimental verification. The results show that the selected three standard diffraction peaks should uniformly span and widely cover the detector to reduce the error of angle calibration. [ABSTRACT FROM AUTHOR]

Analytical expressions of second-order intensity moments and M 2 factors for a conically refracted (CR) Gaussian beam and its components are derived. M 2 for a CR beam is shown to depend on a single parameter, the ratio of the CR ray cylinder radius and the input Gaussian beam waist radius. In typical CR conditions when this ratio is much greater than one, M 2 is also much greater than one even though the divergence angle for a CR beam is the same as for the input Gaussian beam. The increased M 2 value results from the much larger size of CR beam in the focal plane compared with the waist size of input Gaussian beam. M 2 values derived from focal- and Fourier-plane intensity profiles agree with theoretically predicted ones. Second-order moments and M 2 factors of a CR beam and its components are compared with those of Gaussian, Laguerre–Gauss, and modified Bessel–Gauss beams. [ABSTRACT FROM AUTHOR]

A crack or any kind of damage induces a sharp discontinuity in the rotational displacement curve in a structure under load. However, if the beam is not loaded sufficiently or crack depth is very small, the discontinuity may not be possible to identify through conventional methods. This study proposes a non-destructive approach to reveal the presence of a crack in structural components based on the measurement of very small discontinuity in rotational displacement by employing a piezoelectric sensor (PZT). An analytical model of a statically loaded cracked beam with PZT attached to the beam is developed for various boundary conditions. The solution is obtained through Ritz approximation. Rotational displacements at different points along the length of the beam are determined. Subsequently, a finite element analysis on ABAQUS platform is carried out for comparison. The results obtained from these analyses are validated with the experimental data published in open literature. Two distinct techniques are employed to monitor the damage in slender and short length beams. the efficacy of the technique in the detection of small cracks in structure is established. It is also shown that the presence of multiple cracks in beams having various boundary conditions can be monitored by a single non-destructive investigation following the method. [ABSTRACT FROM AUTHOR]

This paper couples the Carrera's Unified Formulation (CUF) with the Asymptotic Numerical Method (ANM) for investigating geometrically nonlinear behaviors of beam structures. On the basis of CUF, a family of advanced one-dimensional beam models is firstly established by deriving a fundamental nucleus. The ANM that is an efficient and robust nonlinear solver is then used to solve the resulted nonlinear systems. Several typical nonlinear problems in thin/thick beam structures are carried out, and numerical results demonstrate the validity and efficiency of the proposed framework. Besides, the importance of using high-order kinematics for beam structures undergoing large deformations is emphasized. [ABSTRACT FROM AUTHOR]

In a recent experimental and theoretical study, the effects of an external light (laser) beam injected in a medium of Kerr-type nonlinearity were studied. It was shown that the system under consideration may undergo to turbulence. In that work, it is claimed that the injected beam may lead to 'random' waves (weak turbulence) and in this case the waves generated are called 'optical wave turbulence'. In this paper, the deterministic model equation proposed is considered. The modification in the proposed equation accounts for the nonlinearity coefficient and the beam wave function to depend on the space variable z is taken. The results found here include various arbitrary functions in z, thus these solutions may lead to randomness in 'some sense'. Also, it has been found that the solutions exhibit a train of incoherent waves, coupled lumps and soliton waves, with gaps. That is, the medium is found to act as a barrier wall that induces optical wave tunneling. This may be argued to the fact that the potential of the injected beam is free. Furthermore, the direction of the reorientation angle is found to be almost everywhere along the direction of light (laser) beam. In other words, a final state is dominated by a single strong soliton whenever a soliton beam is considered. It is shown that the intensity of the wave exhibits an inverse cascade. The results obtained here are completely new. The solutions of the (2 + 1) dimensional equation are derived by using the extended unified method. An algorithm for computing the exact solutions by using Mathematica is presented. [ABSTRACT FROM AUTHOR]

From last few decades, the piezoelectric materials are widely used in the field of structural health monitoring because of its ability for voltage dependent actuation. This paper presents the analytical modeling and simulation of a hybrid (electromagnetic and piezoelectric) energy harvester (having nonlinear behavior) that generates power from vibrations of bridges for structure health monitoring systems. The modeled hybrid energy harvester is comprised of two beams and two tip masses attached to the ends of both beams. Beam 1 consists of a piezoelectric layer and a substrate layer while beam 2 contains a coil and permanent magnet. The two beams are assembled with a specific L shaped geometry. Base excitations are provided in the transverse direction of the first beam of the harvester. The L-shape structure is modeled as a continuous system rather than a lumped-mass system to investigate the dynamic behavior of the structure in more detailed manner. The simulation is performed for both parallel as well as series combinations of the piezoelectric layers. In the case of a parallel combination of piezoelectric layers' maximum voltage of 1.66 V is obtained at the resonance frequency of the structure with 0.2 g acceleration level which resulted in the corresponding power of 65.61 µW. However, in the case of series combination simulation resulted in the production of the maximum voltage of 1.95 V and a corresponding power of 90.54 µW at 0.2 g acceleration level. [ABSTRACT FROM AUTHOR]

In this paper, we study a beam fixed to a base in a translational motion at one end and to a tip mass at its free end. The beam is subject to some vibrations and it is modelled as a Timoshenko structure coupled with a heat equation of hyperbolic type. The only damping we employ is the thermal effect. We come up with a control force capable of driving the system to the equilibrium state in an exponential manner. It is also explained how to get any desirable rate of decay. Our method is based on the multiplier technique. [ABSTRACT FROM AUTHOR]

In this paper, the dynamic modelling and adaptive boundary control of a three-dimensional Timoshenko beam are presented for vibration suppression. In order to ensure that no modal information is left out, partial differential equations (PDEs) are employed to describe the nonlinear dynamic characteristics of the system by applying the extended Hamilton's principle. Based on the established model, barrier Lyapunov functions (BLFs) are utilised for dealing with system output restrictions. For practical consideration, parameter uncertainties and external disturbances are also taken into account. Under the proposed neural adaptive control scheme, undesirable elastic vibration of the three-dimensional Timoshenko beam is restricted and constrained within given bounds even subject to external perturbations, without needing to know any system parameters. The system stability is proved by the Lyapunov's direct method. The control performance is verified via using numerical simulations. [ABSTRACT FROM AUTHOR]

A new static–dynamic equivalence approach for beam bending is developed to determine the critical stability load of a vibrating beam resting on an elastic foundation. It is validated that the critical stability load corresponding to an arbitrary natural frequency parameter can be obtained via both the vibration and the static analysis approaches. By introducing a new elastic foundation stiffness parameter, the natural frequency parameter can be substituted, thus allowing a new formulation to solve the critical stability that corresponds to the zero or negative elastic foundation constant. In the vibration analysis, the governing equation of motion is solved by a harmonic response assumption. In this case, the critical stability loads can be determined by solving the determinant of the dynamic system under different boundary conditions. For zero or negative elastic foundation stiffness, a beam acted by a specific point load on such an elastic foundation can yield an infinite deflection. Under such circumstances, each real natural frequency has an equivalent relationship with the corresponding negative elastic stiffness. Consequently, using this equivalent system, directly solving of the transcendental equation in the dynamic frequency analysis can be avoided. Some numerical examples are presented and it is demonstrated that highly accurate numerical critical stability solutions can be derived by this equivalent static bending approach. The results are validated by comparing with the classical beam buckling solutions. In conclusion, a new theoretical model with analytical solution procedure is put forward and it yields highly convergent numerical solutions that compare well with classical analytical solutions. [ABSTRACT FROM AUTHOR]

Algebraic reconstruction algorithms are a better choice compared to transform-based algorithms whenever projection data is limited in nature. High computational cost and huge memory requirements are two major downsides of iterative reconstruction methods. Among all algebraic techniques, the Multiplicative Algebraic Reconstruction Technique (MART) is most popular because it maximizes the entropy (of the image) in the limiting case. In the present work, our ultimate goal is to reduce computational complexity and cope with the huge storage scenario of the MART algorithm. We propose a new sparse MART algorithm (Sp-MART) and test it with two-dimensional and three-dimensional (2D/3D) numerical data. A more accurate and efficient geometrical formula for calculating intersection length is also presented. Experimental projection data of human tooth and drip irrigation pipe is processed for further validation of the Sp-MART algorithm. Reconstructions of real specimens are also done using the FDK algorithm. The difference between two algorithms are investigated by calculating the structural similarity index (SSIM) and the L2 error of the results. [ABSTRACT FROM AUTHOR]

We propose a semi-analytical scheme for investigating the electromagnetic beam scattering by a uniaxially anisotropic chiral object. The scattered and internal fields are expanded in terms of appropriate spherical vector wave functions, and the method of moments procedure is employed for determining the unknown expansion coefficients. Normalized differential scattering cross sections are evaluated for a uniaxially anisotropic chiral spheroid and circular cylinder of finite length, respectively illuminated by a Gaussian beam, Hermite-Gaussian beam and zero-order Bessel beam. The scattering properties are analyzed briefly. [ABSTRACT FROM AUTHOR]

Based on the fundamental of traditional Sub-aperture coherence (SAC) algorithm, Radial Sub-aperture coherence (RSAC) and Symmetrical Radial Sub-aperture coherence (SRSAC) have been designed to achieve non-mechanical beam steering with ultra-high precision and stability by utilising two-dimensional Liquid Crystal Optical Phased Array (LCOPA). Both of them inherit the original advantages, that is, to eliminate the local pointing accuracy defects and greatly improve the angular resolution of the beam steering system. Meanwhile, the steering angle error caused by the aperture variation and the alignment error can be also effectively restricted by SRSAC. In this paper, the essential mathematical framework of SRSAC and its affiliated local error elimination method was established to supplement the theoretical support of these phase generation algorithms. By dissecting the generation mechanism of each pointing error branch, the theoretical formulae with great universality are finally proposed, which provide visualised and necessary references for the specific application in other beam control situations. [ABSTRACT FROM AUTHOR]

A planar metasurface is designed to replace the traditional three-dimensional axicon lens to generate a nondiffraction in normal direction at first. Then, to generate Bessel beams that can be tilted in any direction, we add the phase distribution information derived from the generalized Snell's reflection law to the traditional axicon phase distribution formula. Finally, a metasurface with a nondiffracting beam inclined to φ of 30° and θ of 30° is designed by employing the final modified phase information for demonstration. The simulated results indicate the effectiveness and robustness of the proposed theory and design. [ABSTRACT FROM AUTHOR]

As the traditional resources (such as frequency, time, and space) are efficiently utilized, it becomes more and more challenging to satisfy the ever-lasting, capacity-growing, and users-boosting demand for wireless networks. Recently, the orthogonal Orbital Angular Momentum (OAM) modes of electromagnetic waves were exploited to achieve high spectral efficiency in radio and microwave transmission. This research discusses the challenges in OAM signal generation, OAM beam divergence, and OAM signal reception misalignment through a new proposed method. A transmission array with arbitrary shape is used to synthesize the desired OAM waveform at a receiver. The receiver, usually in the form of a ring, could have arbitrary size and location in space and therefore the perfect alignment condition, as required between the transmitter and receiver planes, is relaxed. It is also shown that a notable save in the size of the transmission array is gained against other conventionally used OAM generation methods. This could be of great utility in massive Multiple-Input-Multiple-Output (MIMO) systems. Such reduction in the transmitter size along with the flexibility in choosing the receiver size are all exploited to handle the OAM beam divergence problem. The results are shown using mathematical formulas and are checked by comparing them to numerical simulations. [ABSTRACT FROM AUTHOR]

This paper presents a method based on the Moth Flame optimization evolutionary algorithm for the synthesis of Flat-top/pencil beam pair of dual beam reconfigurable concentric circular antenna arrays. This beam pair is generated with the help of the optimized inter-element arc spacing, ring radius and 6-bit discrete radial phases generated by the optimization algorithm. Zero-phases are used for the elements in the pencil beam and the radial phases controlled by the phase shifters are used for generating the flat-top beam. Amplitudes are kept to unity in both the beams. Experiments are carried out using fitness functions that include the side-lobe levels in both the beams along with the beamwidths in the pencil beam and a ripple value in the flat-top portion of the flat-top beam. In addition to it, experiments are also done for providing a null depth in one of the beam pair. The results obtained from the experiments using Matlab software show the effectiveness and superiority of this algorithm over other evolutionary algorithms like Bio-geography-based optimization algorithm and Imperialist competitive algorithms. [ABSTRACT FROM AUTHOR]

This paper explains how the optical quadrupole interaction between a two-level neutral atom and two counter-propagating non-diffracting Bessel beams can exhibit interesting rotational characteristics. It shows that, in this case, the atom dynamics are determined by a radiation pressure force as well as a gradient quadrupole force. Under appropriate circumstances, neutral atoms are able to rotate with zig-zag trajectories in specific spaces inside annular shapes produced by quadrupole potential. This occurs especially when m > 0 Bessel beam. [ABSTRACT FROM AUTHOR]

The fundamental problem of propagation invariant Bessel beams is that they are not square-integrable in the transverse direction, and are therefore associated with an infinite power flux. Hence, truncated Bessel beams are typically considered instead. These are generated by finite apertures or apodized by a Gaussian transmittance. We obtain a different square-integrable solution of the Bessel field distribution. We show that the cylindrical symmetric hollow waveguide as a resonator modulates its own field during its propagation. These fast-decaying modes satisfy Maxwell's equations and can be expressed in analytic form. [ABSTRACT FROM AUTHOR]

A refractive Bessel lattice with micrometric periodicity is induced optically in a photosensitive azobenzene liquid crystal cell of 3 µm thickness by a green 532 nm, 30 mW Bessel beam and with simultaneous illumination by a red 632.8 nm, 15 mW Gaussian beam. The uninterrupted action of both beams plays a key role in the complete mechanism of the refractive lattice formation. The lattice formation is investigated in real-time by the measurement of forward diffracted ring powers from both the red Gaussian and the green Bessel beams. The diffraction efficiency is investigated depending on the green Bessel beam intensity and on the mutual relation between the green beam polarization and the rubbing direction of the cell. A maximum diffraction efficiency of 1.1% is obtained which corresponds to a refractive index change of 6 × 10−3. Simulations are performed and a physical model to explain the experimental results is discussed. [ABSTRACT FROM AUTHOR]

Modulation of Intensity Emerging from Zero Effort (MIEZE) is a neutron resonant spin echo technique which allows one to measure the time correlation functions in materials by modulating the neutron beam using radio-frequency (RF) neutron spin flippers [[1]]. (b) The MIEZE setup with tilted RF flippers, where the tilting angle of the RF flippers needs to satisfy the tilting condition: tan = sin2 . The first approach involves two additional magnetic Wollaston prisms (MWPs) in addition to the two RF flippers [[2]] and the second approach requires the physical tilting of the RF flippers in the primary spectrometer with respect to the beam direction [[3]]. [Extracted from the article]

A detailed variational analysis of single-mode trapezoidal index fibre to investigate its propagation characteristics involving two simple approximations of fundamental mode is presented. It is shown in respect of computation of normalized field that the single parameter variational function having Gaussian and modified Bessel variations in the core and cladding, respectively, is more accurate in comparison with the Gaussian function over a wide range of values of normalized frequency and aspect ratio. Also, it predicts the propagation characteristics, more accurately, than the Gaussian function from variational and recently reported Marcuse-type formulations. Further, in terms of such range of values, a complete formulation of variational parameter for the Gaussian-modified Bessel function is prescribed for ready reference to the system users to predict the modal field and propagation characteristics. [ABSTRACT FROM AUTHOR]

We apply amplitude corrections to a truncated Bessel beam that has propagated through turbulent atmosphere modelled by random phase screens. These corrections are realized via transmitting an unmodulated beam in parallel to the one carrying the 4 amplitude shift keying (ASK) modulated message signal. On the receiver side, the amplitude corrections are obtained by dividing the intensity of the unmodulated beam by its free space equivalence. The corrections are then used to restore the amplitude distortions of the beam carrying the 4ASK modulated message signal and in the determination of decision boundaries for the received 4ASK symbols. The success of the system is visually inspected by comparing the received intensity profiles before and after the application of corrections. Furthermore, simulation analysis of symbol error rate (SER) is made, where the proposed set-up is found to be quite insensitive to wavelength difference between the unmodulated and modulated beams. On the other hand, the difference in the structure constant values of these two beams seems to have profound effect on system performance. [ABSTRACT FROM AUTHOR]

A novel method of laser-controlled shaping of metal microstructures based on the processes of metal atoms adsorption on the surface of crystalline substrate and simultaneous control of photostimulated desorption of atoms by spatially modulated nondiffracting laser beam illumination is presented. The experiments were performed for sodium atoms deposition to the sapphire substrate, which was illuminated by Bessel beam at 532 nm wavelength and 2 W/cm2intensity. Experiments showed that the optical pattern was well reproduced in the sodium deposits thus creating the annularly microstructured metal film with few tens nanometre thickness. [ABSTRACT FROM AUTHOR]

We apply diffractive optical elements in problems of transformation of Bessel beams in a birefringent crystal. Using plane waves expansion we show a significant interference between the ordinary and extraordinary beams due to the energy transfer in the orthogonal transverse components in the nonparaxial mode. A comparative analysis of the merits and lack of diffractive and refractive axicons in problems of formation non-paraxial Bessel beams has shown the preferability of diffractive optics application in crystal optics. The transformation of uniformly polarised Bessel beams in the crystal of Iceland spar in the nonparaxial mode by application of a diffractive axicon is investigated numerically and experimentally. [ABSTRACT FROM AUTHOR]

In this paper, algorithms invariant to position, rotation, noise and non-homogeneous illumination are presented. Here, several manners are studied to generate binary rings mask filters and the corresponding signatures associated to each image. Also, in this work it is shown that digital systems, which are based on the-law non-linear correlation, are-invariant for. The methodologies are tested using greyscale fossil diatoms digital images (real images), and considering the great similarity between those images the results obtained are excellent. The box plot statistical analysis and the computational cost times yield that the Bessel rings masks are the best option when the images contain a homogeneous illumination and the Fourier masks digital system is the right selection when the non-homogeneous illumination and noise is presented in the images. [ABSTRACT FROM AUTHOR]

Debye series expansion is employed to the analysis of radiation pressure force exerted on a spherical particle induced by an axicon-generated Bessel beam. The beam shape coefficients for Bessel beams are calculated using analytical expressions obtained by the integral localized approximation, and the scattering coefficients are expanded using Debye series. The effect of different parameters (beam center location, radius of particle, half-cone angle, etc.) on radiation pressure force is studied. The contributions of different scattering processes on radiation pressure force are isolated for better understanding of physical mechanism of various features of radiation pressure force. [ABSTRACT FROM PUBLISHER]

We present a free space wave structure which under propagation forms a cone shaped intensity distribution along the optical axis. This means that the intensity distribution in the transverse plane is contracting in the course of free space propagation in much the same way as the field propagates in a conical hollow waveguide. The contracting feature of the wave propagation originates from the interference of waves which emerge from a cylindrically symmetric, modulated field structure located initially on a closed spherical shell. This closed wave structure can be called a self-confining wave. [ABSTRACT FROM AUTHOR]

The use of additional adaptive optics to manipulate the beacon in an adaptive optics system for the human eye opens up many opportunities. Possibilities include better beacon creation, correction of gross aberrations that the beam acquires as it passes into the eye, symbiotic beams to guide or locate a probe or medical beam, and examination of the higher order aberrations experienced by the beam as it enters the eye. We describe the use of active optics for creation of the beacon in an adaptive optics system that incorporates a fundus imaging arm. In describing the possibilities for beacon shaping and steps that may be employed to use this to create a sharper or more versatile beacon, we determine the effects of such shaping on the performance of the system. Results are presented for both model and human eyes. The beacon shaping incorporates Bessel beam creation with tip-tilt and defocus correction from a mask on a spatial light modulator. Visual feedback from images of the beacon as it appears at the retina is used to refine it. [ABSTRACT FROM AUTHOR]

In this paper, we demonstrate, numerically and experimentally that using the mask-lens setup used by Durnin to generate Bessel beams Durnin [Phys. Rev. Lett. 58, 1499 (1987)], it is possible to generate different kinds of propagation invariant beams. A modification in the amplitude or phase of the field that illuminates the annular slit is proposed that corresponds to modulation in frequency space. In particular, we characterize the new invariant beams that were obtained by modulating the amplitude of the annular mask and when the incident field was modulated with a one-dimensional quadratic or cubic phase. Experimental results using an amplitude mask are shown in order to corroborate the numerical predictions. [ABSTRACT FROM AUTHOR]