Beam Coupling Research Articles

Nonlinear beam matching to gas-filled multipass cells

Gas-filled multipass cells are an appealing alternative to capillaries to implement nonlinear temporal compression of high energy femtosecond lasers. Here, we provide an analytic expression for stationary beam coupling to multipass cells that takes into account nonlinear propagation. This allows a constant beam size on the mirrors and at the cell waist, thereby making the optical design more accurate, for example to avoid optical damage or significant ionization. The analysis is validated using spatio-temporal numerical simulations of the propagation in a near-concentric configuration. This is particularly important for multipass cells that are operated in a highly nonlinear regime, which is the current trend since it allows a lower number of roundtrips, relaxing the constraint on mirror coatings performance.

Single-mode optical fibers coupling: Study of the field of view

Single mode Fiber (SMF) is commonly used in long distance applications as in optical communication. Coupling of the laser beam into SMF core to get high coupling efficiency is a challenging task in practice. The aim of our work is to study the impact of the field of view on the coupled light beam, taking into account well designed coupling lens to be sure that the focal spot has matched to the mode of propagation.Here in this article, a conical lens of 1.5 refractive index was used for light coupling process. The used criteria at HeNe laser of 0.5438 nm wavelength showed a degradation in the output signal due to generated distortion as the field of view increased from 0 to 6 degrees.

The First Coupling of a Laser Beam to a Water Jet

AbstractAssigned to a project for designing a laser‐based dental hand tool, Bernold Richerzhagen visualized combining a water jet and a laser for tooth ablation. His dental tool envisioned a laser within a low‐pressure hair‐thin water jet that guided the beam by means of total internal reflection in a manner like an optical fiber. Eventually, this fusion of light and water resulted in a new technology capable of machining hard materials with high precision. Starting with a dental tool developed in a Swiss laboratory in 1993, this invention has fostered high‐precision laser machining in the aviation, diamond and semiconductor industries amongst others.

Nonlinear self-trapping and guiding of light at different wavelengths with sheep blood.

We demonstrate the formation of waveguides, a few centimeters long, in colloidal suspensions of sheep red blood cells for a wide range of wavelengths due to nonlinear self-trapping and self-guiding of a laser beam. The near infrared (NIR) light experiences a weaker nonlinear self-action and thus requires much higher power to obtain self-trapping as compared to visible light. To examine the waveguiding of light at different wavelengths, we utilize a pump-probe-type setting for beam coupling: a pump beam at a 532 nm wavelength is used to create a waveguide first, and then a probe beam with various wavelengths is sent through the waveguide channel. Effective guidance for both visible and NIR wavelengths is observed through such otherwise highly scattering bio-soft-matter.

High-Temperature Superconductor Coatings for Beam Impedance Reduction in Particle Colliders: Nonlinear Effects

Coating of surfaces facing particle beams with high-temperature superconductors (HTS) for reducing the beam coupling impedance is being considered for the next generation of hadron colliders, such as the FCC-hh at CERN, where HTS would be exposed to the high-frequency wakefields generated by the particle bunches and to the strong field of the steering magnets. In this frame, we present a simple model for the calculation of the microwave response of HTS exposed to a strong external magnetic field, which takes into account the nonlinearity of the pinning potential of the vortex lattice. The equation of motion of the vortex lattice is solved in first-order approximation, and we calculate the amplitude of the third-harmonic components in the electric field produced by vortex oscillation. We deduce the time-dependent surface impedance, which could serve as a boundary condition in the simulation codes for the calculation of beam-stability phenomena in particle accelerators. Finally, time-integration of the surface impedance allows exploring the dependence of the surface impedance on surface currents, useful for analyzing the experimental results obtained using simple resonators in terms of our model.

Optimization of the focusing characteristics of Fresnel zone plates fabricated with a femtosecond laser

In this research, amplitude Fresnel zone plates (FZPs) were fabricated on fused silica glass with femtosecond laser. The focusing characteristics including focal length, diffraction efficiency, geometric concentrator ratio, spot energy uniformity, depth of focus and resolution were studied by simulations and experiments. To optimize the focusing characteristics of FZP, we proposed an optimized machining process, an extended FZP and an fractal FZP. The optimized machining process increased the diffraction efficiency of the amplitude FZP from 6.96% to 8.14%, the extended FZP broke through the limit of minimum line width in processing and improved the resolution, and the fractal FZP increased the focus depth from 4 mm to 10 mm. In addition, we wrote a FZP on the end face of multi mode fiber, the divergent annular beam converged and formed an focus ring at the focal plane. This research will provide broad applications in fiber tweezers, beam coupling and optical communication.

Spectral-dependent electronic-photonic modeling of high-speed VCSEL-MMF links for optimized launch conditions.

We present spectral-dependent electronic-photonic modeling of vertical-cavity surface-emitting laser (VCSEL)-multimode fiber (MMF) links for next-generation high-speed interconnects. The beam coupling processes, between the VCSEL and the MMF and between the MMF and the photodetector (PD), are discussed, with spectral-dependent three-dimensional launch conditions analyzed. The model accounts for fiber effects on the transmission performance, specifically modal attenuation, dispersion, mode mixing, and mode partition noise. An advanced split-step small-segment (4-S) method simulates the signal evolution over the MMF with high accuracy and high efficiency. Experimental validation at 25 Gbps confirms the high accuracy of the VCSEL-MMF link model. The model reveals that larger radial offsets can further excite lower-order mode groups reducing the power distributed to higher-order groups when a tilted beam couples to the input fiber facet. With an optimized misalignment launch, the modal bandwidth is greatly improved by 3.8-fold compared to the conventional center launch. The model helps determine the optimum launch condition to improve link performance metrics such as transmission reach.

A novel 5-cell strip-line kicker prototype for the HEPS on-axis injection system

Two groups of 10ns-level superfast kickers are needed in the on-axis swap out injection scheme, adopted by the High Energy Photon Source (HEPS) to cope with the very small dynamic aperture of its baseline 7BA lattice design. In order to fit into the very tight longitudinal space in the injection/extraction region, and to relax the strength requirement of the kickers, five units of 300 mm long strip-line kickers are placed into a single stainless-steel vacuum chamber, to form a very compact 5-cell kicker module. Such a novel 5-cell strip-line kicker module design and its prototype development are presented in this paper. The results of the time-domain reflectometer (TDR) test, the high voltage pulse test and the beam coupling impedance test show that the strip-line kickers can meet the requirements of HEPS.

Physics-Informed Neural Network Method for Space Charge Effect in Particle Accelerators

The electromagnetic coupling of a charged particle beam with vacuum chambers is of great interest for beam dynamics studies in the design of a particle accelerator. A deep learning-based method is proposed as a mesh-free numerical approach for solving the field of space charges of a particle beam in a vacuum chamber. Deep neural networks based on the physical model of a relativistic particle beam with transversally nonuniform charge density moving in a vacuum chamber are constructed using this method. A partial differential equation with the Lorentz factor, transverse charge density, and boundary condition is embedded in its loss function. The proposed physics-informed neural network method is applied to round, rectangular, and elliptical vacuum chambers. This is verified in comparison with analytical solutions for coupling impedances of a round Gaussian beam and an elliptical bi-Gaussian beam. The effects of chamber geometries, charge density, beam offset, and energy on the beam coupling impedance are demonstrated.

Research on fatigue crack propagation of metal structure of casting crane based on XFEM

Aiming to solve the crack problem at the connection between the metal diaphragm of the casting crane and the lower cover plate and web, a three-dimensional model of solid-shell coupling of a single main beam is established according to the design drawing of the casting crane, and the crack propagation was simulated using the expansion finite element method (XFEM). The results show that during the crack propagation process at the joint between the diaphragm and the web, the magnitude of the equivalent stress intensity factor ΔKeff is not much different from the magnitude of the type I crack stress intensity factor ΔKI during crack growth at the junction of diaphragm and web weld. The amplitudes of Type II and Type III stress intensity are smaller than those of Type I and equivalent stress intensity factors. In the process of fatigue cracking of the weld between the diaphragm and the web, the type I cracks dominate the role, and the type II and III cracking models have little effect on the connection between the diaphragm and the web.

A Ka-Band Balanced Four-Beam Phased-Array Receiver With Symmetrical Beam-Distribution Network in 65-nm CMOS

This paper demonstrates a Ka-band CMOS phased-array receiver capable of generating four balanced beams from two inputs. A passive four-beam symmetrical differential network is proposed to distribute two input signals to eight channels and facilitate beam generation at the outputs in the receiver. The detailed design and optimization of the passive four-beam differential network are presented. Using a 6-bit passive vector-modulated phase shifter and a 5-bit switched-type attenuator in each channel, we implement a phase control of 360° with<; 4° RMS phase error and a gain control of 17 dB with <; 0.35 dB RMS gain error from 27 to 31 GHz. The receiver consumes a current of only 40 mA under 1 V supply voltage. Eight channels of the four-beam phased-array receiver were measured and a gain mismatch of less than 0.3 dB has been achieved. Beam to beam couplings are investigated by measurements and beam-to-beam isolation are better than 32 dB from 27 to 31 GHz. The chip size is 2.6×4 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> including all digital control circuitry and pads.

Factorization of Antenna Efficiency of Aperture-Type Antenna: Beam Coupling and Two Spillovers

Antenna efficiency is one of the most important figures of merit of a radio telescope for observations, especially at millimeter wavelengths or shorter wavelengths, even for a multibeam radio telescope. To analyze a system with a beam waveguide, a lossless antenna consisting of two apertures in series is considered in the frame of the scalar wave approximation. We found that the antenna efficiency can be evaluated with the field distribution over the second aperture, and the antenna efficiency is factorized into three factors: efficiencies of beam coupling, transmission spillover, and reception spillover. The factorization is applicable to general aperture-type antennas with beam waveguides and can relate the aperture efficiency to the pupil function. We numerically confirmed our factorization with an optical simulation. This evaluation enables us to manage the aberrations and is useful in the design of multibeam radio telescopes.

Mode competition in broad-ridge-waveguide lasers

The lateral brightness achievable with high-power GaAs-based laser diodes having long and broad waveguides is commonly regarded to be limited by the onset of higher-order lateral modes. For the study of the lateral-mode competition two complementary simulation tools are applied, representing different classes of approximations. The first tool bases on a completely incoherent superposition of mode intensities and disregards longitudinal effects like spatial hole burning, whereas the second tool relies on a simplified carrier transport and current flow. Both tools yield agreeing power-current characteristics that fit the data measured for 5–23 µm wide ridges. Also, a similarly good qualitative conformance of the near and far fields is found. However, the threshold of individual modes, the partition of power between them at a given current, and details of the near and far fields show differences. These differences are the consequence of a high sensitivity of the mode competition to details of the models and of the device structure. Nevertheless, it can be concluded concordantly that the brightness rises with increasing ridge width irrespective of the onset of more and more lateral modes. The lateral brightness at 10 MW cm−2 power density on the front facet of the investigated laser with widest ridge (23 µm) is comparable with best values known from much wider broad-area lasers. In addition, we show that one of the simulation tools is able to predict beam steering and coherent beam coupling without introducing any phenomenological coupling coefficient or asymmetries.

Combined influence of beamstrahlung and coupling impedance on beam energy spread and length in future lepton colliders

A semianalytical model has been developed to study a combined effect of beamstrahlung due to beam-beam interaction and beam coupling impedance in the future lepton colliders CEPC and FCC-ee. This model allows evaluating an impact of the coupling impedance on the bunch length and energy spread in collision. The model is benchmarked against numerical simulations. Analytical estimates for the supercolliders are presented.

Multifunctional holographic gratings for simultaneous coupling and beam splitting applications in photonic integrated circuits

A novel holographic grating for simultaneous coupling of power and optical beam splitting application is designed. The proposed design incorporates two identical holo-gratings separated by a distance D. A microscopic object such as micro-sphere or micro-ring is introduced in between these two gratings at a distance $$ \frac{D}{2} $$ and a Gaussian signal is allowed to pass through the first holo-grating which emerges out of the second one. With the proposed design eleven different splitting ratios could be achieved successfully by varying dimension of microscopic objects and the orientations of holo-gratings with respect to plane of incidence. For coupling applications the simulation of the proposed design shows 100% Transmission Efficiency (TE). This leads to an immense flexibility for the use of proposed model in Photonic Integrated Circuits. We demonstrate the possibility of such a multi-functional Holographic device with the aid of Finite Difference Time Domain (FDTD) simulations. To the best of our knowledge, this is the first investigation where simultaneous beam splitting and coupling applications are realized in a holographic optical element.

Self-consistent simulations of beam-beam interaction in future e+e− circular colliders including beamstrahlung and longitudinal coupling impedance

For the past generation ${e}^{+}{e}^{\ensuremath{-}}$ storage ring colliders, we usually used natural bunch length or its impedance lengthened value in beam-beam simulations instead of considering the impedance directly. In the future colliders, such as FCC-ee and CEPC, the beam-beam interaction becomes essentially three dimensional. In order to increase the luminosity, the future accelerators will collide very intense beams of high energy with low emittances and small beta functions at the collision points exploiting the crab waist collision scheme with a large Piwinski angle. For these extreme parameters several new effects become important for the collider performance such as beamstrahlung, coherent X-Z instability, 3D flip-flop so that the longitudinal beam dynamics should be also treated in a self-consistent manner. In this paper we describe the numerical code for the self-consistent 3D beam-beam simulations including beamstrahlung and the longitudinal beam coupling impedance and study interplay of different effects arising in beam-beam collisions of the future colliders.

Optimization of multibeam klystron double gap cavities loaded by metal rods

AbstractIn this paper, the results of numerical investigation of a metal photonic band gap cavity are presented. The investigated resonator is dual‐gap and is considered as an intermediate for the K‐band multibeam klystron. A working mode is a 2n mode with a frequency of 24.15 GHz. Electrodynamic characteristics of the cavity (characteristic impendance, beam coupling factor, relative electronic conductivity, Q‐factor) were calculated and the conditions for achieving the maximum effciency are found. Based on the obtained data, the required number of gaps in the output cavity was estimated, as well as the power and efficiency of the multibeam klystron with this type of cavities, depending on the microperveance of the electron beam.

Study on Load-Side Optimization in Bifrequency MILO Source

In this article, we present an in-depth study of bifrequency magnetically insulated transmission line oscillator (MILO) generating RF output power in S-band with azimuthal partition. It is proposed to optimize the parameters across the load side, inserting gold plate in the collector and tuning the collector cavity depth. The proposal aims at enhancing the power conversion efficiency by employing the concept of a tapered extraction region and implementing four stubs. The stubs help to achieve proper impedance matching, subsequently improving the output power. Further, loss-free FR-4 dielectric is used in extractor vanes which helps to reduce the RF power distribution in other modes. The use of gold plate stimulates space charge near the surface and helps in deflecting the electrons toward the interaction cavities. The presence of FR-4 extractor vane helps to generate spoke current near the collector. The proposed system provides improvised RF coupling of the electron beam to the interaction cavities. The peak power efficiency of ~12.7% is achieved through the device. The beam–wave interaction process is illustrated using space charge instability mechanism. Taking into account the Lagrangian of electrons relationship between angular momentum and torque due to angular force is also derived. This in-depth study helps in the deep understanding of magnetic insulation process inside the device toward developing the proficient MILO source.

Study on stability and bifurcation of electromagnet-track beam coupling system for EMS maglev vehicle

The stability and bifurcation behavior of the electromagnet-track beam coupling system of the electromagnetic suspension maglev vehicle are studied by the theoretical and numerical analyses. The stability domain of three key dynamics parameters of the track beam as well as the Lyapunov coefficient at the degenerated equilibrium point is calculated. The topological structure of the solution to the coupling system near the Bautin bifurcation point is determined. The results show that in the engineering practice, the intermediate frequency should be avoided in the natural frequency of the track beam; when a low frequency is taken, it should be reduced as much as possible; when a high frequency is taken, it should be increased as much as possible and the damping ratio should also be increased, so that the system can remain stable while a lighter-weight track beam is used, thereby reducing the engineering costs. Besides, when the parameters are near the Bautin bifurcation point, the system will have complex dynamics behaviors. Within a certain parameter range, multiple stable and unstable limit cycles exist simultaneously, so that the system tends to have different stable solutions under different initial disturbances.

Mode interaction in cold‐formed steel members: state‐of‐art report

AbstractExtended keynote paper of Eurosteel 2021This two‐part paper provides a state‐of‐art report on the most recent findings concerning the behaviour, strength and Direct Strength Method (DSM) design of cold‐formed steel (CFS) columns and beams affected by mode coupling phenomena not adequately covered by the current specifications for CFS members, namely local‐distortional (L‐D), local‐distortional‐global (L‐D‐G), distortional‐global (D‐G) and global‐global (flexural‐torsional/flexural – FT‐F) interaction. The paper addresses experimental tests, numerical simulations and DSM‐based design approaches that are intended to i) acquire in‐depth knowledge on the non‐linear behaviour (elastic and elastic‐plastic), load‐carrying capacity and failure mode nature of the members under consideration, and ii) make use of that knowledge to develop, propose and assess the merit of efficient DSM‐based design approaches to estimate their failure loads/moments. Initially, illustrative column results are briefly presented to help grasp some fundamental concepts, namely the characterisation of i) the aforementioned mode coupling phenomena, ii) different sources of mode interaction that may lead to failure load/moment erosion, and iii) the most detrimental initial geometrical imperfections. The DSM design curves currently codified and two strength curves recently developed for column flexural‐torsional and beam distortional failures are presented next. The two‐part paper then addresses separately each mode coupling phenomenon dealt with, for columns, but only L‐D and D‐G interaction for beams – while L‐D interaction (in columns and beams) appears in Part 1, the remaining column and beam coupling phenomena (all involving global buckling) are dealt with in Part 2 [1]. For columns undergoing L‐D and L‐D‐G interaction, beams experiencing L‐D interaction and angle columns susceptible to FT‐F interaction, the work reported includes experimental studies, numerical simulations and DSM‐based design considerations and/or guidelines. For the remaining coupling phenomena, only numerical results are reported, but they unveil interesting (and unexpected) behavioural features that will help plan future test campaigns and achieve efficient design approaches. Finally, the two‐part paper closes with a few concluding remarks and an outlook regarding future developments in this field.