Effect Of Beam Parameters Research Articles

Subnanoscale Ion Beam Modification-Assisted Smoothing of Heterostructure Surfaces.

Glass ceramic (GC) is the most promising material for objective lenses for extreme ultraviolet lithography that must meet the subnanometer precision, which is characterized by low values of high spatial frequency surface roughness (HSFR). However, the HSFR of GC is typically degraded during ion beam figuring (IBF). Herein, a developed method for constructing molecular dynamics (MD) models of GC was presented, and the formation mechanisms of surface morphologies were investigated. The results indicated that the generation of the dot-like microstructure was the result of the difference in the erosion rate caused by the difference in the intrinsic properties between ceramic phases (CPs) and glass phases (GPs). Further, the difference in the microstructure of the IBF surface under different beam angles was mainly caused by the difference in the two types of sputtering. Quantum mechanical calculations showed that the presence of interstitial atoms would result in electron rearrangement and that the electron localization can lead to a reduction in CP stability. To obtain a homogeneous surface, the effects of beam parameters on the heterogeneous surface were systematically investigated based on the proposed MD model. Then, a novel ion beam modification (IBM) method was proposed and demonstrated by TEM and GIXRD. The range of ion beam smoothing parameters that could effectively converge the HSFR of the modified surface was determined through numerous experiments. Using the optimized beam parameters, an ultrathin homogeneous modified surface within 3 nm was obtained. The HSFR of GC smoothed by ion beam modification-assisted smoothing (IBMS) dropped from 0.348 to 0.090 nm, a 74% reduction. These research results offer a deeper understanding of the morphology formation mechanisms of the GC surfaces involved in ion beam processing and may point to a new approach for achieving ultrasmooth heterostructure surfaces down to the subnanometer scale.

Propagation of hollow higher-order cosh-Gaussian beam in oceanic turbulence

The averaged received intensity of hollow higher-order cosh-Gaussian (HHOCG) beam propagating in oceanic turbulence is derived based on extended Huygens–Fresnel integral. In detail, the effect of beam parameters and oceanic turbulence parameters on the received intensity is analyzed. Interestingly, beam has a focusing nature along propagation. Our results indicate that received intensity distribution is not affected from the variation in source field parameters. Beam size at the receiver plane can vary according to the changes in turbulence nature. Accordingly, the provided results will contribute to the improvement of both underwater optical communication and imaging systems.

Near-field electromagnetic scattering of Bessel vortex beam by metal target

Bessel vortex beam, as a typical vortex beam, has the characteristics of carrying orbital angular momentum (OAM), no diffraction, and self-reconstruction, which makes it more competitive than plane wave in the field of future vortex beam target detection and imaging. In order to study the near-field electromagnetic scattering of a vortex beam by a metal target, the expression of the near-scattering field of Bessel vortex beam incident on any metal target is obtained by using the physical optics method, triangular surface element modeling, and the plane wave angular spectrum expansion method of vector Bessel vortex beam. The correctness of the proposed method is verified by comparing with the simulation results of FEKO software. The amplitude distribution and phase distribution of electric field, the OAM spectrum distribution and radar cross section (RCS) of the near-scattering field of the Bessel vortex beam incident on the simple target and the combined target are calculated. The effects of beam parameters, receiving distance, target shape and the positions of beam transmitting and receiving surfaces on near-field scattering results are numerically calculated. In addition, the distributions of near-field OAM spectra under different conditions and the near-field RCS distributions of different targets are given. The numerical results show that the near-field results of Bessel vortex beam incident on metal targets are related to the beam parameters, and conform to the law of Bessel beam changing with parameters. The near-field electric amplitude distribution is affected by the distance between the receiving surface and the target, but the phase distribution is hardly affected. The near-field scattering results reflect the changes of target shape. Under normal incidence, when the target is regular and symmetrical, the amplitude distribution and phase distribution are relatively regular, and the main mode is dominant. When the beam is obliquely incident on or does not fully illuminate the target, the amplitude distribution and phase distribution change, which will lead the derived mode to increase. In particular, when the target and the receiving surface both deviate from the incident beam, the OAM disturbance is the most severe. In the near-field RCS distribution, the RCS distributions of different targets are obviously different, and the results of <i>E</i> plane and <i>H</i> plane are also different. It can be seen from the numerical calculation results that the near-field scattering of Bessel vortex beam by a metal target contains a variety of information. The application of vortex electromagnetic wave will help improve the information acquisition of electromagnetic wave and target detection capability. The results in this work can provide a reference for target imaging and vortex radar detection.

Analysis of radiation force on a uniaxial anisotropic sphere by dual zero-order Bessel beams

Based on the generalized Lorenz–Mie theory (GLMT), a theoretical approach is introduced to study the radiation force exerted on a uniaxial anisotropic sphere illuminated by dual zero-order Bessel beams (ZOBBs). The beams propagate with arbitrary direction, and are expanded in terms of the spherical vector wave functions (SVWFs) in the particle coordinate system using the coordinate rotation theorem. The total expansion coefficients of the incident fields are derived by superposition of the vector fields. Applying the Maxwell’s stress tensor, the analytical expressions of the radiation forces on a homogeneous absorbing uniaxial anisotropic sphere are derived. Comparing the radiation forces of dual ZOBBs with those results of dual ZOBBs simplified into single ZOBBs and dual plane waves, the accuracy and correctness of the theory are verified. In order to study the equilibrium state, the effects of beam parameters, particle size parameters, and anisotropy parameters on the radiation forces are discussed in detail. Comparing with the isotropic particle, the equilibrium status is sensitive to the anisotropic parameters. Moreover, the properties of optical force on a uniaxial anisotropic sphere in single ZOBB trap and zero-order Bessel standing wave trap are compared. The theory and results of this paper are hopeful to provide an effective theoretical basis for the study of optical micromanipulation of biological and anisotropic complex particles by multi-beams.

Analysis of radiation force on a uniaxial anisotropic sphere by dual counter-propagating Gaussian beams.

Based on Maxwell's stress tensor and the generalized Lorenz-Mie theory, a theoretical approach is introduced to study the radiation force exerted on a uniaxial anisotropic sphere illuminated by dual counter-propagating (CP) Gaussian beams. The beams propagate with arbitrary direction and are expanded in terms of the spherical vector wave functions (SVWFs) in a particle coordinate system using the coordinate rotation theorem of the SVWFs. The total expansion coefficients of the incident fields are derived by superposition of the vector fields. Using Maxwell stress tensor analysis, the analytical expressions of the radiation force on a homogeneous absorbing uniaxial anisotropic sphere are obtained. The accuracy of the theory is verified by comparing the radiation forces of the anisotropic sphere reduced to the special cases of an isotropic sphere. In order to study the equilibrium state, the effects of beam parameters, particle size parameters, and anisotropy parameters on the radiation force are discussed in detail. Compared with the isotropic particle, the equilibrium status is sensitive to the anisotropic parameters. Moreover, the properties of optical force on a uniaxial anisotropic sphere in a single Gaussian beam trap and Gaussian standing wave trap are compared. It indicates that the CP Gaussian beam trap may more easily capture or confine the anisotropic particle. However, the radiation force exerted on an anisotropic sphere exhibits very different properties when the beams do not propagate along the primary optical axis. The influence of the anisotropic parameter on the radiation force by CP Gaussian beams is different from that of a single Gaussian beam. In summary, even for anisotropic particles, the Gaussian standing wave trap also exhibits significant advantages when compared with the single Gaussian beam trap. The theoretical predictions of radiation forces exerted on a uniaxial anisotropic sphere by dual Gaussian beams provide effective ways to achieve the improvement of optical tweezers as well as the capture, suspension, and high-precision delivery of anisotropic particles.

Vortex modulation of a linearly polarized Lorentz- Gauss Airy Beam

In this paper, focusing characteristics of the linearly polarized Lorentz-Gauss vortex Airy beam was studied. With other parameters unchanged, as the number of topological charges increases, the focal spot map will split regularly, gradually splitting from the center into two symmetrical points. The light field in the central area changes regularly and can be used to calculate the number of charges. The effect of beam parameters on light spot fission was studied. The results show that the effect of Lorentz-Gauss parameters on fission is much greater than Airy parameters. By changing the parameters of Lorentz-Gauss, the fission process of light spots can be significantly changed, and new Light intensity distribution.

Radial phased-locked multi-Gaussian Schell-model beam array and its properties in oceanic turbulence

The radial phased-locked multi-Gaussian Schell-model (MGSM) beam array composed by the N MGSM beamlets is first given to describe a new laser array. The evolution properties of radial phased-locked MGSM beam array in free space and oceanic turbulence are discussed in detail. Based on the extended Huygens-Fresnel principle, the MCF and the effective size of radial phased-locked MGSM beam array in oceanic turbulence are derived. The effects of beam parameters and the oceanic turbulence parameters on the spreading and spectral degree of coherence of radial phased-locked MGSM beam array propagating in oceanic turbulence are investigated by using numerical examples. This research may be useful in underwater optical wireless optical communication.

Propagation properties of radially polarized multi-Gaussian Schell-model beams in oceanic turbulence.

By utilizing the extended Huygens-Fresnel principle, we derive the analytical formulas for the cross-spectral density matrix elements of a radially polarized multi-Gaussian Schell-model (RPMGSM) beam propagating in oceanic turbulence. Effects of beam parameters and oceanic turbulence parameters on the propagation properties of RPMGSM beams are investigated in detail by numerical simulation. Our results show that the RPMGSM beam with larger beam order M has an advantage over the radially polarized Gaussian Schell-model beam for reducing turbulence-induced degradation. Compared with temperature-induced turbulence fluctuation, the salinity-induced turbulence fluctuation makes a greater contribution to the influence on propagation properties of RPMGSM beams.

Model of a rectangular multi-Gaussian Schell-model vortex beam and its properties

Considering the theory of coherence, the rectangular multi-Gaussian Schell-model vortex beam (RMGSMV) beam generated by multi-Gaussian Schell-model source has been introduced, and the propagation properties of RMGSMV beam propagating in free space has been analyzed by using the derived equations. The effects of beam parameters on the properties of RMGSMV beam propagating in free space have been discussed. The results show that the RMGSMV beam propagating in free space can remain the dark hollow center at the short propagation distance, and the beam will gradually evolve into a beam with similar rectangular flat-topped profile as the propagation distance increases.

Focal pattern evolution of azimuthally polarized lorentz-gaussian vortex beam

We present in principle and demonstrate experimentally the focal performance of a new azimuthally polarized Lorentz-Gaussian vortex beam rigorously from different dimensions. Based on vector diffraction theory, the expressions for the electric fields of this beam are derived. The effect of beam parameters on focal pattern evolution is explored. Based on the modulation of beam parameters, ideal beam shaping can be realized in azimuthally polarized Lorentz-Gaussian vortex beam. Additionally, we adopt phase-only spatial light modulator in Fourier space to exhibit desired beam with specific parameters through computer-generated hologram (CGH). According to the conclusions either in theory or experiment, more and more application points about vector beams would be excavated.

Elastica of Non-Prismatic and Nonlinear Elastic Cantilever Beams under Combined Loading

This study presents the elastica of non-prismatic cantilever beams with rectangular cross-sections that are subjected to combined loading. The considered beams are nonlinearly elastic and obey Ludwick’s constitutive law. The combined loading system used in this study provides uniform loading, tip point loading, and tip couple loading individually or in combination. This loading system can create a total of seven loading cases that have not been covered in the literature. Ordinary differential equations governing the large deformed shapes of the elastica of the beams are derived and solved numerically. The effects of beam parameters on elastica behavior, including tip responses and strains and stresses loaded onto the cross-sections, were studied. It was observed that the exponential constant of the mechanical properties is very sensitive to elastica behavior. The results also demonstrate that the stresses near the neutral axis are larger with a larger exponential constant.

Analysis and Optimization of the Characteristics of Superpower Virtode Generation

We report on the results of the 3D numerical simulation of perspective design of an oscillator based on an external-feedback virtual cathode (virtode), as well as optimization of characteristics of its generation. We have analyzed the effect of beam parameters on the virtode output characteristics. In particular, we have obtained the dependence of the efficiency on the feeding voltage and on the current being injected. We have studied the effect of beam velocity premodulation and electron velocity spread on virtode generation characteristics. It has been established that the introduction of premodulation sharply increases the generation efficiency up to 13% for optimal parameters. The possibility of stable generation in the virtode at relatively large spread in electron velocities has been demonstrated.

Focal pattern evolution of radially polarized Lorentz-Gaussian vortex beam

Focusing properties of linearly radially Lorentz-Gaussian vortex beams was investigated, in which all three orthogonal field components were considered in research. The focal pattern distorts considerably and regularly on increasing charge number for certain parameters, and there are two intensity peaks locating weak intensity ring along one coordinate direction. Distance between two intensity peaks increases on increasing charge number, which may be used to measure charge number. The effect of beam parameters on focal pattern evolution was also studied, which shows that effect of Gauss parameter is more considerably than that of Lorentz parameter. The focal pattern evolution direction can be changed by increasing Gauss parameter, which may results in novel intensity distributions.

Propagation properties of Gaussian Schell-model array beams in non-Kolmogorov turbulence

A stochastic beam generated by a recently introduced Gaussian Schell-model array (GSMA) source (2015 Opt. Lett. 40 5662) is investigated. We derive the analytical propagation formulae for the spectral density and the propagation factor in non-Kolmogorov turbulence by utilizing the extended Huygens–Fresnel principle and second-order moments of the Wigner distribution function. Numerical results show that the lattice patterns of GSMA beams, which keep propagation-invariant in free space, are destroyed by the turbulence at sufficiently large distances. The GSMA beams have significant advantage over the Gaussian Schell-model beam in the robustness of the destructive effect of non-Kolmogorov turbulence, especially for the GSMA beam with more lattice elements and bigger relative separation distance of each lattice element. The effects of beam parameters and non-Kolmogorov turbulence on the propagation factor are analyzed in detail.

An improved molecular structure mechanics method and its application for graphene wrinkling

This paper proposes an improved molecular structure mechanics (iMSM) method to study the wrinkling characteristics of annular graphene sheet (AGS). An idea of variable cross-section beam, combined with 3-node Timoshenko beam, is introduced in the iMSM model for considering the flexibility of C-C bond and C-C joint simultaneously, and the stiffness matrix of beam element is deduced for later calculation. The parameters of equivalent beam are obtained by using an interior point optimization approach. Based on the proposed iMSM model, the wrinkling characteristics of AGS are simulated, which are verified by molecular dynamic (MD) simulation. A predicted model is used to evaluate the wrinkling level of AGS, which agrees well with the iMSM simulation, and then the effects of beam parameters on graphene wrinkling are also analyzed. The results indicate that our proposed model is reliable to the wrinkling analysis of AGS and may be further used for other researches on graphene.

Effect of beam parameters on the space charge wave modes in slow wave structures with semi-circular and trapezoidal corrugation

Corrugated waveguide with sinusoidal shape has long been used as slow wave structure (SWS) in backward wave oscillators (BWOs). Alternative SWSs with arbitrary geometries such as trapezoidal and semi-circular have drawn the attention of the researchers recently to be used as interaction regions in BWOs. In this work, the zero and non-zero beam dispersion characteristics of the axisymmetric transverse magnetic (TM) modes of semi-circularly and trapezoidally corrugated SWS (SCCSWS and TCSWS) have been studied numerically. The effect of variation of the electron beam parameters such as beam energy, current and radius on space charge wave modes (SCWM) and temporal growth rate (TGR) has also been investigated rigorously. The simulation results provide detail information regarding the unstable region where the resonant interaction occurs which is the requirement for microwave generation.

Single-crystal diamond micro-cupped resonators made by laser ablation

This paper presents a novel three-dimensional fabrication process of micro-scale shell resonator made of single-crystal diamond (SCD) called micro-cupped resonator (MCR). The key feature of the process is the application of laser ablation, which can contribute to the shaping process of SCD with higher accuracy, better structural symmetry, greater speed, and lower breakage rate. UV laser high precision processing machine has been employed for the ablation of SCD in the present investigation. This paper describes the principle of laser ablation of SCD and analyses the effects of beam parameters on ablation quality. Then MCR with better structural symmetry and less structural imperfection has been successfully fabricated based on optimum parameters by laser ablation. The MCR is promising for emerging applications such as micro rate-integrating gyroscope.

Diffraction of Lorentz-Gauss beam in uniaxial crystals: orthogonal to optical axis

Based on the diffraction theory of beams in uniaxial crystals, diffraction properties of a Lorentz-Gauss beam in uniaxial crystals orthogonal to the optical axis are derived in analytical forms. Diffraction fields, intensity distributions and effects of beam parameters are investigated by numerical examples, respectively. Results show that, upon propagation, initial field components and intensity distributions of Lorentz-Gauss beams would deteriorate due to effects of anisotropic media. When the Lorentz-Gauss beam diffracts into the far field, its intensity distribution would convert into a four-petal profile. Beam parameters w x and w y are shown to have a strong influence on intensity distributions. By selecting different values of them, profiles of Lorentz-Gauss beams would be different upon propagation.

Erosion of solid surface under irradiation by high-power submicrosecond ion beams

The erosion of a solid surface under high-power pulsed ion beams is considered. The values of atom yield from an irradiated surface due to the evaporation are obtained by numerical simulation. The effect of beam parameters and target characteristics on atom emission intensity was investigated. The technological capabilities of high-power submicrosecond ion beams for solid surface etching are assessed.

Scattering for Charged Multisphere Structure Located in Plane Wave/Gaussian Beam

Scattering characteristics for charged multisphere structure illuminated by a plane wave/a Gaussian beam are studied on the basis of generalized Lorenz-Mie theory. The incident, internal and scattered fields for each sphere in an arbitrarily incident Gaussian beam are expressed in terms of vector spherical wave functions (VSWFS) expansion form. Making use of the vector addition theorem of VSWFS, the scattering coefficients of total scattered fields for charged multisphere structure are deduced in detail. Taking charged carbon particles and water droplets for examples, numerical results of scattering intensity for different quantities of electric charge are shown and compared with uncharged case. A discussion of the effect of beam parameters on scattering intensity is presented.