Beam Mode Research Articles

Biaxial Gaussian Beams, Hermite–Gaussian Beams, and Laguerre–Gaussian Vortex Beams in Isotropy-Broken Materials

We have developed the paraxial approximation for electromagnetic fields in arbitrary isotropy-broken media in terms of the ray–wave tilt and the curvature of materials’ Fresnel wave surfaces. We have obtained solutions of the paraxial equation in the form of biaxial Gaussian beams, which is a novel class of electromagnetic field distributions in generic isotropy-broken materials. Such beams have been previously observed experimentally and numerically in hyperbolic metamaterials but have evaded theoretical analysis in the literature up to now. Biaxial Gaussian beams have two axes: one in the direction of the Abraham momentum, corresponding to the ray propagation, and another in the direction of the Minkowski momentum, corresponding to the wave propagation, in agreement with the recent theory of refraction, ray–wave tilt, and hidden momentum [Durach, 2024]. We show that the curvature of the wavefronts in the biaxial Gaussian beams correspond to the curvature of the Fresnel wave surface at the central wave vector of the beam. We obtain the higher-order modes of the biaxial beams, including the biaxial Hermite–Gaussian and Laguerre–Gaussian vortex beams, which opens avenues toward studies of the optical angular momentum (OAM) in isotropy-broken media, including generic anisotropic and bianisotropic materials.

Composite underwater optical wireless channel modeling based on the electric field Monte Carlo method

In this study, we propose a simulation method to investigate the scattering characteristics of beams with specific phase structures in waters containing micrometer-scale particles and bubbles. This method is based on the electric field Monte Carlo (EMC) algorithm and utilizes the Mie theory and ray tracing method. We simulate the propagation of orbital angular momentum (OAM) beams in a composite underwater channel using the proposed method and analyze the impact of bubble density on the spiral phase distribution of the OAM beams. We also design an underwater experiment in a water tank to simulate the propagation of OAM beams in the composite channel. The results reveal that the power of the desired mode of the OAM beam decreases as the bubble density increases, which is consistent with the simulation results. This method facilitates a realistic simulation of structured light beam propagation in waters containing particles and bubbles and can provide reference data for studying the scattering characteristics of structured beams in composite underwater channels.

Influence of adjustable ring modes on molten pool behavior and microstructure of Al–Si coated boron steel in fiber laser welding

The influence of adjustable ring modes on the phase transition and microstructural evolution in conduction mode laser welding of Al–Si coated boron steel was investigated. Distinct geometric variations and molten pool behavior were observed through a ring-shaped beam effect. The ring beam introduced by ring-beam-mode (RBM) and dual-beam-mode (DBM) laser welding inhibited Al segregation into the fusion zone (FZ). The ring beam caused the Al molten particles to be driven towards the outer boundaries of the weld pool. A ring-beam-mode (RBM) and a dual-beam-mode (DBM) laser welding inhibited Al segregation into the FZ, resulting from a minimal temperature gradient and extension of the solidification time. Phase transition calculations demonstrated that a mount of residual ferrite within the FZ is significantly correlated with the Al concentration at specific temperature points, indicating a predominant role of a central-beam-mode (CBM) FZ in δ-ferrite formation. The RBM and DBM effectively suppressed Al segregation into the FZ, leading to a reduction in ferrite formation and the development of a refined microstructure characterized by a uniform and high density of geometrically necessary dislocations. Electron backscattered diffraction (EBSD) analysis revealed a higher proportion of low-angle grain boundaries in the RBM and DBM, attributed to the unique thermal distribution induced by the ring beam. These findings highlight the critical role of beam mode in tailoring the microstructure and properties of laser welds in Al–Si coated boron steel.

Cylindrical Vector Beams with an MOPA Amplifier Based on Nonlinear Polarization Rotation Mode-Locking

CVBs (cylindrical vector beams) are widely used in optical imaging, optical trapping, material processing, etc. In this study, based on mode-selective couplers and passive mode-locking fiber technology, a cylindrical vector fiber amplifier with an MOPA (master oscillator power amplifier) structure was developed. In the experiment, the pre-amp stage reached 19.87 mW output power and a CVB output with a mode purity greater than 97%. The measured beam quality factor was M2 = 2.1. The CVB output power obtained by the first-amp stage was 152.4 mW, and the mode purity was greater than 92%. The measured beam quality factor was M2 = 1.99. The internal inhomogeneity and external effects of the isotropic LMA (large-mode-area) fiber led to a decrease in beam quality and mode purity. After amplification, the gain of the fundamental mode was higher and the power was greater, resulting in a greatly reduced mode purity. This CVB fiber amplifier yielded important research value in expanding the applications of high-power fiber lasers.

Optical trapping forces exerted by a pulsed Hermite–Gaussian beam on a dielectric nanosphere

An analytical expression for the optical forces exerted by a pulsed Hermite–Gaussian (HG) beam on a nano-dielectric sphere has been derived. This allows us to investigate how the forces are affected by different beam modes (p,l) and the duration of the light pulse (τ). Our findings demonstrate that these factors significantly influence the strength of the forces, the number of regions where the sphere can be trapped, and the size of these trapping zones. This knowledge paves the way for precise control of these tiny particles with light, potentially leading to improved techniques for trapping and sorting nanoparticles.

Bending response and energy absorption of sandwich beams with combined reinforced auxetic honeycomb core

This study introduces a reinforced star-shaped auxetic honeycomb (RSSAH) sandwich beam, enhanced with hollow thin-walled tubes to improve bending resistance and energy absorption performance. The bending performance of the RSSAH is systematically investigated through quasi-static three-point bending tests and finite element numerical simulations. The findings suggest that when subjected to mid-span stress, the RSSAH displays both localized indentation and overall bending deformation, accompanied by notable negative Poisson’s ratio (NPR) impact under bending loads. Parametric studies are undertaken by numerical simulations to investigate the impact of compression position, auxetic angle, and face sheet thickness on the bending mode of the auxetic honeycomb sandwich beam. The analysis shows that the RSSAH can exhibit excellent bending performance and, at one of the compression positions, displays double-plateau stress characteristics. It is also found that altering key geometric parameters, such as the auxetic angle and panel thickness ratio, can greatly improve the bending capabilities of the RSSAH, achieving stable plastic deformation and high energy absorption. Finally, compared to star-triangle honeycomb (STH) sandwich beam, traditional reentrant honeycomb (RH) sandwich beam and star-shaped auxetic honeycomb (SSAH) sandwich beam, the RSSAH demonstrates superior bending performance and energy absorption capacity. This study offers insights and references for the development of innovative reinforced auxetic honeycomb sandwich beams.

Numerical analysis of load-bearing capacity of shear-strengthened reinforced concrete beams without shear reinforcement using side-bonded CFRP sheets

As CFRP (carbon fiber-reinforced polymer) offers high retrofit efficiency for structural members in bending and shear due to its superior mechanical properties compared to steel, sheets made from this material have become ubiquitous in strengthening existing reinforced concrete (RC) structures. However, there needs to be more research on RC beams with no stirrups that have been shear-strengthened with side-bonded CFRP sheets. As such, this study aims to investigate this specific topic and assess design-related parameters that impact the load-bearing capacity of these shear-strengthened beams. To achieve this, nonlinear finite element models of four RC beams, including one control beam and three beams strengthened with side-bonded CFRP sheets, were built and verified regarding shear capacity, crack patterns, and failure mechanisms. The simulated beams demonstrated a high level of accuracy in all mentioned aspects. Numerical models were then developed to evaluate the design-oriented parameters that affect the response of shear-strengthened beams, including the concrete compressive strength, the amount of steel reinforcement, the number of CFRP layers, the CFRP bonding configuration, and the shear span-to-effective depth ratio. The results showed that not only the compressive strength of the concrete but also the amount of steel longitudinal reinforcement had a significant relationship with the load-bearing capacity of shear-strengthened beams. Meanwhile, the bonding configuration and the layer number of side-bonded CFRP sheets considerably influenced the ductility, the crack pattern, and the failure mode of shear-strengthened beams.

Switchable phase modulation and multifunctional metasurface with vanadium dioxide layer

Abstract Metasurface, comprising subwavelength unit cells, offers a flexible modulation of the optical phase. However, traditional metasurfaces are typically engineered to function solely in one mode, limiting their efficiency and adaptability. In this study, we proposed a switchable metasurface consisting of gold bars deposited on polyimide and vanadium dioxide (VO2) layer. Upon the phase transition of VO2, this switchable metasurface exhibits functionality in both transmissive and reflective modes. Specifically, it efficiently converts left circularly polarized (LCP) light into right circularly polarized (RCP) light. For the dielectric (metallic) phases of VO2, the design behaves as metalens with a focal length of 1000 (906) μm at working frequency of 1.2 THz, respectively. Furthermore, the vortex phase can be effectively manipulated with topological number from 1 to 4 through the analysis of the electric field distribution. A directional emission from 12.9° to 42.2° is obtained in the reflective mode and Airy beam paths way can also be well regulated at 1.49 THz. The phase modulation is further achieved by varying the inter-mediums and its thickness. Finally, the sensing ability is explored with different covered solution. Consequently, this multifunctional and adaptable metasurface offers valuable insights for the development of reflectors, modulators, lenses and sensors.

Electromechanical coupling optimization for a sandwich beam activation using piezoceramics

Sandwich beams composed of two stiff carbon fiber skins and a viscoelastic core are often used to passively dissipate energy through the activation of shearing in a specific frequency range. Semi-active or active energy dissipation can be made possible on those structures adding piezoelectric patches, coupling mechanical vibration energy and electrical energy. J.L. Guyader et al. [jsv, 1978] theorized a frequency dependent equivalent dynamic model of a sandwich structure, recently extended to the homogenization of anisotropic multi-layers by F.Marchetti et al. [jsv, 2020]. This frequency-dependent stiffness of the beam has to be taken into account in the piezoceramic thickness definition in order to optimize the global electromechanical coupling coefficient. An analytical model is derived from the works of F.Marchetti et al. and adapted to predict the first vibration mode of a finite cantilever beam instrumented with a piezoelectric patch. The electromechanical coupling evolution is then calculated with the proper boundary conditions and for different PZT ceramic thicknesses. This model is furtherly used to define the best transducer configuration for a given sandwich structure beam.

Experimental and numerical investigation of low‐velocity impact behavior and failure mode of shear deficient RC beam strengthened with CFRP strips

AbstractIt is well‐known that shear failure is a collapse mechanism that is the riskiest, fastest, and catastrophic and occurs with no visible signs of damage or prior warning for RC beams. Therefore, to prevent brittle shear failure, the RC beams should include sufficient shear reinforcement, such as stirrups, and be designed to have sufficient shear capacity. However, the RC beams' shear capacity becomes inadequate for various reasons. One of these reasons may be the acting of the impulsive impact load, which is uncommon and disregarded in the design phase on the RC beams. An experimental program was conducted to examine the impact behavior and failure mode of shear‐deficient RC beams in the scope of the present study. Besides, it aims to investigate the effectiveness of the strengthening method using CFRP strips in improving the general behavior, failure mode, and performance of shear‐deficient RC beams exposed to impact load. The time histories of the accelerations, displacements, impact loads, and strains in the CFRP strips were measured. They were interpreted how they are affected by experimental variables examined in the experimental study. Furthermore, the finite element model of the specimens was generated in the LS‐DYNA software, and the experimental and numerical results were compared by performing finite element analysis in terms of failure modes and general behavior.

Application of Low Modulus CFRP Fabric for Steel Beams Strengthening: Experimental and Design Validation

This paper presents experimental results of steel beams strengthened with low-density and low-modulus CFRP fabrics, with the objective of, (i) checking the capability of the fabric type CFRP in strengthening; (ii) assessing and understanding the failure modes for design improvement; and (iii) validating the design methods for the practical application. A total of eighteen full-scale 2.5-meter-long beams strengthened with CFRP were tested. The governing failure modes of the CFRP-strengthened steel beams were debonding, rupture, and wrinkling. The experimental moment capacities were compared with the design predictions using the limit state suggested in the ACI guideline and two new design limit states. The comparison of design predictions indicated that the use of the limit state suggested in the ACI guideline unconservatively predicted the design moment capacity while the two new design limit states were conservative. Further, it is evidently assessed that the low modulus CFRP fabric can be used for the strength upgrade of the steel beams. A detailed design example is presented for the CFRP-strengthened steel beam using different limit states for a better understanding of the readers.

Experiment and numerical simulation on bearing capacity of partial steel-ultra-high-performance concrete continuous composite beams

Due to high strength, toughness and durability, ultra-high-performance concrete (UHPC) can be applied in replacing the cracked concrete slab in the negative moment region of newly built steel-ordinary concrete (OC) continuous composite beams, as well as in repairing old composite beams. To investigate the failure mode, crack propagation, stiffness degradation and bearing capacity of the partial steel-UHPC continuous composite beam, a test model with an UHPC slab over the negative moment region were designed and fabricated to compare with a steel-OC model with the same conditions. Similar failure mode was observed in the loading test of two models. Nevertheless, the maximum crack width in the UHPC slab is only 0.17 mm, much smaller than that in the OC slab. Compared with the steel-OC composite beam, vertical deflection of the partial steel-UHPC composite beam decreases by 32.7 %, and its cracking load and ultimate bearing capacity increase by 50 % and 6.4 %, respectively. The results show that the substitution of the OC with the UHPC in the negative bending moment area significantly improves the crack resistance, delays the crack propagation, increases the bending stiffness, and improves the working performance of composite beams with cracks, displaying good advantages in economy and in reality. Parametric analysis demonstrates that the height of steel beam is the most important factor, and cross section of the steel beam is suggested to be given priority in design so as to take advantages of partial steel-UHPC composite beams. The research also provides an option for the repair of old concrete slabs in steel-OC continuous composite beams.

Switching of three-dimensional optical cages using spatial coherence engineering

Precisely capturing and manipulating microparticles is the key to exploring microscopic mysteries. Optical tweezers play a crucial role in facilitating these tasks. However, existing optical tweezers are limited by their dependence on specific beam modes, which restrict their ability to flexibly switch and manipulate optical traps, thereby limiting their application in complex scientific challenges. Here, we propose a new method to achieve type switching and manipulation of optical traps using a single structured beam via optical coherence engineering. A conjugate-model random structured beam with a switch is designed. By altering the state of the switch, we can change the type of optical cage, enabling the capture of different particle types. Furthermore, the range, strength, and position of the optical trap can be controlled by adjusting the initial beam parameters. We hope that optical coherence engineering will extend the capabilities of existing structured optical tweezers, paving the way for advances in future optical tweezers applications.

Strong–strong simulations of combined beam–beam and wakefield effects in the Electron–Ion-Collider

Collective wakefield and beam–beam effects play an important role in accelerator design and operation. These effects can cause beam instability, emittance growth, and luminosity degradation, and warrant careful study during accelerator design. In this paper, we studied the combined wakefield and beam–beam effects in an Electron Ion Collider design using strong–strong simulations. The simulation results show that the nonlinear beam–beam effects help suppress wakefield driven instability in the nominal working tune regime. In other tune regimes, the coherent beam–beam modes interact with the wakefields and cause a beam instability. The simulation results also show the importance of maintaining nominal crab cavity voltage. If the crab cavity voltage drops significantly the beam can become unstable.

Research Progress on Precision Tool Alignment Technology in Machining

In the field of numerical control machining, tool alignment technology is a key link to ensure machining accuracy and quality. Tool alignment refers to determining the correct position of the tool relative to the workpiece, and its accuracy directly affects the precision of part machining. With the development of precision machining technology, the research and application of cutting technology are increasingly valued. Tool alignment methods are mainly divided into two categories: contact and non-contact. The contact type tool alignment method relies on direct contact between the tool and the workpiece or tool alignment instrument to measure the position. Among them, the trial cutting method is a traditional contact type tool alignment method that determines the tool position through actual cutting, which is intuitive but inefficient. The contact type tool presetter uses specialized equipment to improve the accuracy and efficiency of tool presetting through contact measurement. The non-contact tool alignment method does not rely on physical contact, while the image method uses image recognition technology to determine the tool position, making it suitable for high-precision applications. The laser diffraction method and the laser direct method use laser technology for non-contact measurement. The laser diffraction method determines the position of the tool by analyzing the diffraction mode of the laser beam, while the laser direct method directly measures the distance between the laser and the tool. This article mainly introduces the classification of tool alignment, commonly used knife alignment methods and common tool alignment devices, as well as the development status of international tool alignment instrument products.

Numerical investigation on flexural performance of dowel laminated timber with laminas made of laminated veneer lumber

Horizontal dowel laminated timber (H-DLT) is a doweled engineered wood product with laminas made of solid timber. H-DLT has excellent bending resistance. However, the height of cross-section of H-DLT as a beam is limited by the width of solid wood laminas. Laminated veneer lumber (LVL) is an engineered wood product formed by hot-pressed gluing thin veneers, which is flexible in cross-section size compared to solid timber. Horizontal dowel laminated veneer lumber (H-DLVL) was developed by utilizing the H-DLT production methods and LVL material characteristics. H-DLVL has flexible size and good mechanical properties, and it can be made into beams and panels with large cross-sections. In this paper, the flexural performance of H-DLVL beams was investigated. A predictive finite element model of H-DLVL beams was created by the extended finite element method (XFEM) with cohesive zone model (CZM). The numerical models using solid-beam elements without fictitious cracks were verified and calibrated by experimental results. The influence of five variables, including lamina width, thickness, and quantity, dowel spacing along the grain, and dowel row (edge distance), on the flexural performance of H-DLVL beams was analyzed, and the flexural strength of H-DLVL beams was parameterized. The results showed that the failure mode of H-DLVL beams could be well predicted by XFEM without considering fictitious cracks combined with CZM, and the error range of simulated flexural strength of H-DLVL beams was within ±10 %. The flexural strength of H-DLVL beams was directly affected by lamina thickness and dowel spacing along the grain. The flexural strength of H-DLVL beams increased with the increase of those two variables. Lamina width and dowel row (edge distance) affected the flexural strength of H-DLVL beams indirectly by influencing the failure mode of H-DLVL beams. Based on this research, the recommended dowel spacing along the grain of H-DLVL beams was 6.25–12.5 times the wood dowel diameter, and the recommended edge distance of H-DLVL beams was 5–7 times.

Experimental and numerical study on flexural performance of ultra-high performance concrete frame beams reinforced with steel-FRP composite bars

This paper presents the bending tests of four ultra-high performance concrete (UHPC) frame beams and one normal strength concrete (NSC) frame beam, all reinforced with steel-FRP composite bars (SFCBs). A comprehensive analysis was carried out, encompassing evaluation of the failure mode, crack propagation, bearing capacity, deformation, strain response, and plastic rotational capacity of the frame beams. Investigating the effects of concrete type, reinforcement type, and beam-end reinforcement ratio on the flexural performance of the frame beams was a key aspect of this study. A three-dimensional finite element (FE) model of the frame beam was established and rigorously verified. The developed model enabled a detailed parametric analysis involving the steel ratio, the yield strength of the inner core steel bar, the elastic modulus of the FRP, and the ultimate tensile strength of the SFCB. The results indicated a consistent failure mode of all frame beams: crushing of concrete at the beam-end, initiating a sequence of plastic hinge occurrence starting at the beam-end and then progressing to mid-span. The substitution of normal strength concrete with UHPC significantly enhanced various aspects of the frame beams, including the flexural capacity, deformation, ductility, ultimate energy dissipation, and plastic rotational capacity, while inhibiting the generation and expansion of cracks. Notably, the plastic rotation angle of SFCB-UHPC frame beams was 4.9 times greater than those of steel-UHPC frame beams, emphasizing the effectiveness of SFCB in enhancing the beam-end plastic rotational capacity. A decrease in the beam-end reinforcement ratio significantly reduced the flexural capacity, ultimate energy dissipation, and beam-end plastic rotational capacity, while improving ductility. Additionally, the study established a formula for calculating the equivalent plastic hinge length, utilizing the relative compressive zone height and effective section height of the beam-end controlling section as variables, which demonstrated good alignment between predicted and experimental results.

Reconfigurable mode converter based on a Sb2Se3 phase change material and inverse design

In this paper, we combine the inverse design with a silicon-Sb2Se3 hybrid platform to design an on-chip mode converter that converts basic modes to higher-order modes. Firstly, we present a 1 × 2 mode converter with dimensions of 4.8 × 2.7 µm2 that enables TE0 mode input, TE0 or TE1 output in the C-band (1530 nm to 1565 nm) with an insertion loss (IL) of less than 0.8 dB and a crosstalk (CT) of less than -13 dB. Secondly, the device is extended to a 1 × 3 switchable three-mode converter. Using two controllable phase change regions as drivers, it can flexibly control the switching from TE0 mode input to three modes of TE0, TE1, or TE2 outputs, which enables mode switching and signal routing. The device can be switched between three modes and has broad application potential in broadband optical signal processing for mode division multiplexing systems, as well as optical interconnections. Finally, the device is extended to a 1 × 2 controllable (mode and power) beam splitter, which can control the power ratio between output modes. By modulating the crystallinity of Sb2Se3, the simulation achieves a multilevel switching of 36 levels (> 5-bit). These devices pave the way for high integration densities in future photonic chips.

Compact mid-infrared dual-wavelength optical parametric oscillator pumped by Yb-doped fiber lasers based on two PPMgLN crystals

A compact mid-infrared (MIR) dual-wavelength optical parametric oscillator (OPO) pumped by Yb-doped fiber lasers (YDFLs) based on dual-crystal with an L-shaped cavity structure is demonstrated. Two periodically poled MgO-doped lithium niobite (PPMgLN) crystals with polarization periods of 30.44 μm and 28.96 μm are pumped by two YDFLs, respectively. The dual-wavelength output at 3.45 μm and 4.00 μm is obtained synchronously by adjusting the double pump power. When the total power of double-end pumping is 28.98 W with a ratio of 2:3, the pulse width is 60.80 ns under the repetition frequency of 110 kHz, the output power is 1.483 W@3.45 μm and 1.703 W@4.00 μm, respectively. The total conversion efficiency is 10.99%. By utilizing this cavity structure, the gain and wavelength tuning of the two OPOs can be controlled separately. Meanwhile, the pulse width is 46.93 ns@3.45 μm and 39.38 ns@4.00 μm, respectively. The laser beam quality closely approaches the theoretical quality of the fundamental mode beam. Additionally, by independently adjusting the temperature of the two PPMgLN crystals from 20 °C to 150 °C, tunable mid-infrared laser outputs with wavelengths of 3.448–3.272 μm and 4.006–3.864 μm are achieved. The corresponding tuning bandwidths are 176 nm and 142 nm, respectively.

Polarization-Mode Transformation of the Light Field during Diffraction on Amplitude Binary Gratings

In this paper, a comparative analysis and numerical simulation of operation of two types of amplitude binary gratings (conventional and fork), both in the focal plane and near-field diffraction under illumination by mode beams with different polarization states, were performed. The simulation of the field formation in the focal plane was performed using the Richards–Wolf formalism. The diffraction calculation in the near-field diffraction was performed based on the FDTD method, considering the 3D structure of optical elements. The possibility of multiplying the incident beam in different diffraction orders of binary gratings and the polarization transformation associated with spin–orbit interaction at tight focusing were shown. In this case, various polarization transformations were formed in ±1 diffraction orders of the fork grating due to different signs of the introduced vortex-like phase singularity. The obtained results can be useful for the laser processing of materials and surface structuring.