Use Of Beams Research Articles

Impact of non-Gaussian beam profiles in the performance of hadron colliders

At the Large Hadron Collider (LHC), the interplay between a series of effects, including intrabeam scattering (IBS), synchrotron radiation, longitudinal beam manipulations, two beam effects (beam-beam, e-cloud) and machine non-linearities, can change the population of the core and tails and lead to non-Gaussian beam distributions, at different periods during the beam cycle. By employing generalised distribution functions, it can be demonstrated that the modified non-Gaussian beam profiles have an impact in the beam emittance evolution by itself and thereby to the collider luminosity. This paper focuses on the estimation of beam distribution modification and the resulting rms beam size due to the combined effect of IBS and synchrotron radiation by employing a Monte-Carlo simulation code which is able to track 3D generalised particle distributions (SIRE). The code is first benchmarked over classical semi-analytical IBS theories and then compared with measurements from the LHC at injection and collision energies, including projections for the High-Luminosity LHC (HL-LHC) high brightness regime. The impact of the distribution shape on the evolution of the bunch characteristics and machine performance is finally addressed.

Tracking atomic structure evolution during directed electron beam induced Si-atom motion in graphene via deep machine learning

Using electron beam manipulation, we enable deterministic motion of individual Si atoms in graphene along predefined trajectories. Structural evolution during the dopant motion was explored, providing information on changes of the Si atom neighborhood during atomic motion and providing statistical information of possible defect configurations. The combination of a Gaussian mixture model and principal component analysis applied to the deep learning-processed experimental data allowed disentangling of the atomic distortions for two different graphene sublattices. This approach demonstrates the potential of e-beam manipulation to create defect libraries of multiple realizations of the same defect and explore the potential of symmetry breaking physics. The rapid image analytics enabled via a deep learning network further empowers instrumentation for e-beam controlled atom-by-atom fabrication. The analysis described in the paper can be reproduced via an interactive Jupyter notebook at https://git.io/JJ3Bx

Tunable optical metasurfaces enabled by chalcogenide phase-change materials: from the visible to the THz

Metasurfaces and nanoantennas are redefining what can be achieved in terms of optical beam manipulation, as they provide a versatile design platform towards moulding the flow of light at will. Yet, once a conventional metasurface is designed and realised, its effect on optical beams is repeatable and stationary, thus its performance is ‘locked-in’ at the fabrication stage. A much wider range of applications, such as dynamic beam steering, reconfigurable and dynamic lensing, optical modulation and reconfigurable spectral filtering, could be achieved if real-time tuning of metasurface optical properties were possible. Chalcogenide phase-change materials, because of their rather unique ability to undergo abrupt, repeatable and non-volatile changes in optical properties when switched between their amorphous and crystalline phases, have in recent years been combined with metasurface architectures to provide a promising platform for the achievement of dynamic tunability. In this paper, the concept of dynamically tunable phase-change metasurfaces is introduced, and recent results spanning the electromagnetic spectrum from the visible right through to the THz regime are presented and discussed. The progress, potential applications, and possible future perspectives of phase-change metasurface technology are highlighted, and requirements for the successful implementation of real-world applications are discussed.

Comparative investigations of multi-fidelity modeling on performance of electrostatically-actuated cracked micro-beams

Silicon is a commonly used material for the fabrication of beams for use in micro-electrical-mechanical systems (MEMS). Although silicon is a brittle material, it has been shown to accumulate fatigue damage at the micro-scale. Understanding the effect this has on the overall device performance is critical to the design of reliable devices. Analytical methods for modeling damage provide expedient results but are limited by broad modeling assumptions. Numerical models account for more detailed physical phenomena but can be computationally intensive. In this work, two different crack scenarios are modeled using both analytical techniques and 3D computational simulations. First, the effects of a single surface crack on the static deflection and natural frequency of an electrostatically actuated micro-beam are formulated and compared. Then, a new method for approximating damage associated with realistic distributed crack networks is formulated for use in an analytical model and numerical simulations. A method for utilizing experimentally derived crack statistics to inform the analytical and numerical distributed crack models is developed. Good agreement between the analytical and numerical models is obtained for both crack scenarios. Together, these models can be used to effectively simulate a variety of damage and fatigue behaviors in silicon-based MEMS devices.

Design of a multichannel photonic crystal dielectric laser accelerator

To be useful for most scientific and medical applications, compact particle accelerators will require much higher average current than enabled by current architectures. For this purpose, we propose a photonic crystal architecture for a dielectric laser accelerator, referred to as a multi-input multi-output silicon accelerator (MIMOSA), that enables simultaneous acceleration of multiple electron beams, increasing the total electron throughput by at least 1 order of magnitude. To achieve this, we show that the photonic crystal must support a mode at the Γ point in reciprocal space, with a normalized frequency equal to the normalized speed of the phase-matched electron. We show that the figure of merit of the MIMOSA can be inferred from the eigenmodes of the corresponding infinitely periodic structure, which provides a powerful approach to design such devices. Additionally, we extend the MIMOSA architecture to electron deflectors and other electron manipulation functionalities. These additional functionalities, combined with the increased electron throughput of these devices, permit all-optical on-chip manipulation of electron beams in a fully integrated architecture compatible with current fabrication technologies, which opens the way to unconventional electron beam shaping, imaging, and radiation generation.

Generation and manipulation of spiral beams in photovoltaic photorefractive crystal twinning with mirroring diffusion management

The dynamics characteristics of spiral beams composed of two coherent solitons in photovoltaic photorefractive crystal twinning with mirroring diffusion management are investigated. The numerical simulations show that the orbits of spiral beams depend on the co-effect of the diffusion and coherence effects, and that spiral beams are forcedly rotated around the propagation axis set inside the twinning plane. Moreover, when the incident position of two coherent solitons relative to the twinning plane is reversed, the rotation direction of spiral beams is reversed accordingly. Furthermore, when the initial separation between (peak intensity of) two coherent solitons is adjusted, the rotation speed of spiral beams is adjusted accordingly.

Dark solitons in the inhomogeneous self-defocusing Kerr media

In this paper, the dynamics of dark solitons in inhomogeneous self-defocusing Kerr-media are explored by utilizing the nonlinear Schrödinger (NLS) equation with variable coefficients. Firstly, the mathematical model with variable coefficients is simplified to the standard NLS equation with constant coefficients, by using the self-similar transformation. Then, the bilinear Hirota method is employed to treat the model and the first- and second-order dark soliton solutions are obtained. Different cases of dark solitons with variable coefficients are presented graphically. The results show that the behavior of dark solitons can be effectively controlled by adjusting the loss, diffraction and nonlinear coefficients. It is believed that these results can be used for beam manipulation and all-optical switching, and could be helpful for improving the transmission fidelity of dark solitons in inhomogeneous self-defocusing Kerr media.

Secondary ion mass spectrometry using energetic cluster ion beams: Toward highly sensitive imaging mass spectrometry

Imaging mass spectrometry (IMS), based on linking mass-analysis data for ions and their original positions in a sample, allows the visualization of the spatial distribution of atomic and/or molecular species in the sample, and is therefore an essential analytical method for the characterization of chemical and biological materials. For sensitive elemental and chemical imaging using IMS, a sufficient amount of ions to be analyzed should be supplied from the analyzing area on the sample surface. Secondary ion mass spectrometry (SIMS) using energetic cluster ions (ECIs) with energies of sub-MeV and above as primary ions (ECI-SIMS) can provide the secondary ions necessary for the characterization of organic materials with high emission yields. Hence, ECI-SIMS is a good method for highly sensitive IMS. We report recent progress in ECI beam manipulation techniques for applications of ECI-SIMS to highly sensitive IMS together with the characteristics of ECI impacts on organic materials.

Novel method for the generation of stable radiation from free-electron lasers at high repetition rates

For more than a decade free-electron lasers (FELs) have been in operation, providing scientists from many disciplines with the benefits of ultrashort, nearly transversely coherent radiation pulses with wavelengths down to the \AA{}ngstrom range. If no further techniques are applied, the FEL will only amplify radiation from the stochastic distributed electron density in the electron bunch. Contemporary developments aim at producing stable and single-mode radiation by preparing an electron bunch with favorable longitudinal electron density distributions using magnets and conventional laser pulses (seed), hence the name ``seeding.'' In recent years, short wavelength FELs at high electron beam energies and high repetition rates were proposed and built. At those repetition rates, an external seed with sufficient power to manipulate the electron beam cannot be provided by present state-of-the-art laser systems, thus no external seeding scheme could be applied yet. In this paper, we present ways to seed FELs to generate short wavelength radiation at high repetition rates, making use of tested electron beam manipulation schemes. For our parameter study, we used the parameters of FLASH, the free-electron laser in Hamburg. First simulations are presented, showing the feasibility of the method proposed.

Methods and algorithms for computer synthesis of holographic elements to obtain a complex impulse response of optical information processing systems based on modern spatial light modulators

The possibilities of designing optical devices for data processing and imaging based on the manipulation of coherent light beams by means of spatial light modulators (SLMs) are investigated. A review of commercially available SLMs is presented and the limitations of their complex modulation characteristics are analysed. The main problem of using present-day SLMs is the lack of the ability to modulate directly all states within a unit circle in the complex plane. In this regard, the characteristics of current methods for the synthesis of holographic elements are described that implement a given complex impulse response of the optical system and are optimal for using SLMs with purely amplitude, purely phase, and hybrid amplitude – phase modulation.

Summary of European Advanced Accelerator Workshop (EAAC) Working Group 1: Electron Beams from Plasma

We summarize oral contributions presented in Working Group (WG) 1 of the European Advanced Accelerator Workshop (EAAC). Working Group 1 is titled ’Electron Beams from Plasma’ and included presentations and discussions on the following subjects: laser- and beam-driven plasma wakefield acceleration, recent experimental results and planned experiments, single and multi drive laser pulses (or particle bunches), external and self-injection techniques, staging as well as advanced beam control and manipulation.

The UA9 setup for the double-crystal experiment in CERN-SPS

Experiments to measure the electric and the magnetic moments of short-lived baryons using an internal target and two bent crystals in the vicinity of one of the existing LHC detectors were recently proposed, in the frame of the Physics Beyond Colliders Working Group at CERN. Investigating fixed-target physics in the LHC with in-vacuum solid targets is an unprecedented challenge. As a preparatory step, the layout of the UA9 experiment, installed in the CERN SPS to explore beam manipulations assisted by bent crystals, has been modified to study the feasibility of the double-crystal scenario in a circular accelerator. Ideally, the first crystal should capture halo protons in channeling states directing them onto the internal target to produce rare baryons, whilst the second crystal, located just downstream of the target, should channel the baryons, rotate their polarization vector and deflect them towards the detector area. The upgraded UA9 layout is presented. Preliminary measurements providing an insight of the beam behavior are reported.

Multifunctional Beam Manipulation at Telecommunication Wavelengths Enabled by an All‐Dielectric Metasurface Doublet

AbstractMultifunctional metasurfaces, which are planar devices featuring diverse functionalities, have attracted tremendous attention as they enable highly dense integration and miniaturization of photonic devices. Previous approaches based on spatial/spectral multiplexing of meta‐atoms on single metasurfaces are supposed to be inevitably limited in their functional diversity. An additional degree of freedom for design, achieved by cascading multiple metasurfaces into a single metasystem, promotes new combinations of functions that cannot be achieved with single‐layered metasurfaces. In this study, an all‐dielectric metasurface doublet (MD) is developed and implemented by vertically concatenating two arrays of rectangular nanoresonators on either side of a quartz substrate, in which distinct phase profiles are encoded for transverse magnetic and transverse electric polarized light. Multifunctional beam manipulation with concurrent increased beam deflection, beam reduction, and polarizing beam splitting is achieved at telecommunication wavelengths near 1550 nm. The MD is accurately created via lithographical nanofabrication, thus eliminating the extremely demanding post‐fabrication alignment. The proposed multifunctional metasurface is highly anticipated to expedite the development of advanced technologies for large‐scale photonic integration, optical metrology, light detection and ranging, spectroscopy, and optical processing.

Dynamic Airy imaging through high-efficiency broadband phase microelements by femtosecond laser direct writing

Manipulating Airy beams to symmetric Airy beams (SABs) with abruptly autofocusing and self-accelerating properties has attracted much attention. With such a particular propagation dynamic, SABs may provide great potential in dynamic signal imaging. On the other hand, the generation of SABs by spatial light modulators suffers from the limitations of phase gradient accuracy, low optical efficiency ( < 40 % ), and a bulky footprint. Therefore, exploring imaging applications and optimal generation methods of these Airy-type beams deserves further research. Here, based on the coordinate transformation of SAB, an asymmetric Airy beam (AAB) is realized. Symmetric/asymmetric cubic phase microplates (SCPPs/ACPPs) are designed and fabricated for generating SAB/AAB. The SCPP/ACPP demonstrates superior performance: compact construction ( 60 μm × 60 μm × 1.1 μm ), continuous variation of phase, high efficiency ( ∼ 81 % at 532 nm), and broadband operation from 405 to 780 nm. Dynamic imaging under monochromatic and polychromatic lights is realized by the SAB/AAB, indicating various results at different propagation distances with a certain initial signal. Further investigation reveals that the SCPP on a soft substrate maintains its physical dimensions and optical properties unchanged during stretching. Our work enables wide potential applications in integrated optics, beam manipulation, and imaging.

Observation of the Relativistic Reversal of the Ponderomotive Potential.

The secular dynamics of a nonrelativistic charged particle in an electromagnetic wave can be described by the ponderomotive potential. Although ponderomotive electron-laser interactions at relativistic velocities are important for emerging technologies from laser-based particle accelerators to laser-enhanced electron microscopy, the effects of special relativity on the interaction have only been studied theoretically. Here, we use a transmission electron microscope to measure the position-dependent phase shift imparted to a relativistic electron wave function when it traverses a standing laser wave. The kinetic energy of the electrons is varied between 80 and 300keV, and the laser standing wave has a continuous-wave intensity of 175 GW/cm^{2}. In contrast to the nonrelativistic case, we demonstrate that the phase shift depends on both the electron velocity and the wave polarization, confirming the predictions of a quasiclassical theory of the interaction. Remarkably, if the electron's speed is greater than 1/sqrt[2] of the speed of light, the phase shift at the electric field nodes of the wave can exceed that at the antinodes. In this case there exists a polarization such that the phase shifts at the nodes and antinodes are equal, and the electron does not experience Kapitza-Dirac diffraction. Our results thus provide new capabilities for coherent electron beam manipulation.

Singular Points of Polarizations in the Momentum Space of Photonic Crystal Slabs.

Bound states in the continuum (BICs), circularly polarized states (C points) and degenerate states are all of three types of singular points of polarization in the momentum space. For photonic crystal slabs (PhCSs) with linearly polarized far fields, BICs were found to be the centers of polarization vortices and attracted more attention in the previous studies. Here, we theoretically demonstrate that the far fields of PhCSs can exhibit remarkably diverse polarizations due to the robust existences of C points in the continuum. Only a pair of C points with identical handedness and opposite topological charge can be annihilated together. Continuously fine tuning of the structure parameters of PhCSs without breaking their symmetry, a pair of C points with identical topological charge and opposite handedness are able to merge into a BIC, then the BIC splits into C points again. Interestingly, a Dirac-degenerate BIC with one-half of topological charge is observed when two pairs of C points with identical topological charge from the upper and lower band, respectively, simultaneously merge at the Dirac-degenerate point. The law of topological charge conservation is verified to play an important role in the evolutions and interconversions between different types of polarization singularities. Our findings might shed light on the origin of singular points of polarization, could open a gateway towards the applications of them in the generation and manipulation of vector beams.

Dual-band terahertz switch based on EIT/Fano effect

Terahertz system requires dynamic manipulation of terahertz wave, however, quite a few terahertz wave devices are static, and their functions are fixed after fabrication. We realize a dual-band terahertz switch based on electromagnetic induced transparency (EIT) and Fano effect through change the operating temperature. It consists of two rectangular strips, VO2-embedded rectangular-split ring, and silicon substrate. The extinction ratios of the dual-band terahertz switch at 0.480 THz and 0.675 THz are 20.5 dB and 12.2 dB, respectively. Our approach can be used to design dynamic multi-wavelength terahertz beam manipulation devices.

Manipulation of Airy Beams in Dynamic Parabolic Potentials

AbstractThe propagation of finite energy Airy beams in dynamic parabolic potentials, including uniformly moving, accelerating, and oscillating potentials, is investigated. The propagation trajectories of Airy beams are strongly affected by the dynamic potentials, but the periodic inversion of the beam remains invariant. The results may broaden the potential applications of Airy beams, and also enlighten ideas on Airy beam manipulation in nonlinear regimes.

Terahertz accelerator based electron and x-ray sources

The generation and use of THz radiation for electron acceleration and manipulation of electron bunches has progressed over the last decade to a level where practical devices for THz guns, acceleration and a wide range of beam manipulations have become possible. Here, we present our progress on generation of single-cycle THz pulses at the two-hundred micro-Joule level to drive advanced acceleration and beam manipulation devices. Specifically, we use pulses centered at 0.3 THz to power a segmented terahertz electron accelerator and manipulator (STEAM) capable of performing multiple high-field operations on the 6D-phase-space of ultrashort electron bunches. Using this STEAM device, we demonstrate record THz-acceleration of >60 keV, streaking with <10 𝑓s resolution, focusing with >2 kT/m strength, compression to ~100 𝑓s as well as real-time switching between these modes of operation. The STEAM device demonstrates the feasibility of THz-based electron accelerators, manipulators and diagnostic tools enabling science beyond current resolution frontiers with transformative impact.

Arbitrary Diffraction Engineering With Multilayered Multielement Metagratings

We theoretically formulate and experimentally demonstrate an analytical formalism for the design of printed circuit board (PCB) metagratings (MGs) exercising individual control over the amplitude and phase of numerous diffracted modes, in both reflection and transmission. Lately, these periodic arrangements of subwavelength polarizable particles (meta-atoms) were shown to deflect an incoming plane wave to prescribed angles with very high efficiencies, despite their sparsity with respect to conventional metasurfaces. Nonetheless, most reported MGs were designed based on full-wave optimization of the meta-atoms, with the scarce analytical schemes leading directly to realizable devices were restricted to single-layer reflecting structures, controlling only the partition of power. In this paper, we present an analytical model for plane-wave interaction with a general multilayered multielement MG, composed of an arbitrary number of meta-atoms distributed across an arbitrary number of layers in a given stratified media configuration. For a desired (forward and backward) diffraction pattern, we formulate suitable constraints, identify the required number of degrees of freedom, and correspondingly set them to yield a detailed MG configuration implementing the prescribed functionality; no full-wave optimization is involved. To verify and demonstrate the versatility of this systematic approach, fabrication-ready multilayer PCB MGs for perfect anomalous refraction and non-local focusing are synthesized, fabricated, and experimentally characterized, for the first time to the best of our knowledge, indicating very good correspondence with theoretical predictions. This appealing semianalytical methodology is expected to accelerate the development of MGs and extend the relevant range of applications, yielding practical MG designs on demand for arbitrary beam manipulation.