Beam Divergence Research Articles

Response of negative ion beamlet width and axis deflection to RF field in beam extraction region

Beam-divergence characteristics of single negative ion beamlet have been experimentally investigated with a superimposition of a controlled perturbation of a radio frequency wave (RF) field in a filament-arc discharge negative ion source. Oscillations of a negative-ion beamlet width and axis responding to the RF perturbation were observed, which may be a cause of the larger beam divergence angle of the RF negative ion source for ITER. It is pointed out that the oscillation of the beamlet width depends on the perveance and on an RF frequency such that the oscillation is suppressed at perveance-matched conditions and at low RF frequency.

Mode Division Multiplexing Free Space Optical Communication System Performance with Aperture Averaging in Atmospheric Turbulence and Various Weather Conditions

Due to the serious challenge for mobile operators as a result of spectrum congestion in radio frequency spectrum, free space optical (FSO) communication has been considered a timeous alternative especially for future generation high capacity wireless networks. Although FSO offers advantages such as huge data carrying capacity among others, it suffers from the drawback of atmospheric turbulence and adverse weather conditions. As a mitigation to this problem, mode division multiplexing (MDM) has been another research direction. This paper proposes the design and numerical simulation of a hybrid modified duobinary return to zero (MDRZ) MDM free space optical communication system, which to the best of the authors’ knowledge has not been a subject of investigation. The performance metrics used are the bit error rate, quality factor and received optical power. Two modes, HG00 and HG01 were investigated and compared. It has been observed that the BER, Q factor and received power degrades as we increase the beam divergence, FSO transmission distance and data rate. Moreover, the performance gap between clear and moderate weather conditions is more for HG00 than for HG01 for the same considered data rates. The aperture averaging has been shown to be a strong mitigation strategy especially in foggy conditions.

Low‐profile circular‐polarized fractal antenna design with reduced orbital angular momentum beam divergence

AbstractThe authors introduce a novel low‐profile circular‐polarized three‐layer fractal antenna design to reduce beam divergence in orbital angular momentum (OAM) applications at microwave frequencies. The top layer of the proposed design has a printed Koch fractal antenna that is coupled to a rotated rectangular patch antenna in the mid‐layer fed through a microstrip line. The bottom layer consists of a metallic ground plane to improve beam collimation. The antenna was developed from a new fractal geometry generated in Scilab™. Characteristic mode theory was used in the antenna design to obtain two orthogonal current modes in quadrature that generate circular polarization with OAM fields of order l = –1 at 5.88 GHz. The proposed fractal antenna system has good potential to improve the performance of microwave OAM systems.

Toward a storage ring coherent light source based on an angular dispersion-induced microbunching scheme.

The combination of reversible angular dispersion-induced microbunching (ADM) and the rapid damping storage ring provides a storage-ring-based light source with the capability to produce longitudinal coherent radiation with a high repetition rate. This paper presents a prototype design for a test facility based on the study by Jiang et al. [Sci. Rep. (2022), 12, 3325]. The modulation-demodulation section is inserted into a long straight section of the storage ring instead of a bypass line, which poses great challenges for the optimization of the nonlinear dynamics of the storage ring. However, this design avoids the challenging injection and extraction system connecting to the bypass line. To utilize mature laser technology and reduce the difficulty of the reversible ADM lattice design, we use a long-wavelength 1030 nm seed laser. In the simulation, we achieved 20th harmonic radiation with a bunching factor of about 7.2%. The growth rate of vertical emittance and energy spread of the electron beam for a single pass are about 11% and 0.02%, respectively. When the energy of the electron beam is 800 MeV and two sets of damping wigglers are employed, the damping time in the vertical plane is reduced to 8.31 ms. This results in a 438 kHz repetition rate of the coherent radiation at the new equilibrium state.

Spatial coherence measurement of divergent x-ray beam without prerequisite source information

Abstract Understanding the spatial coherence of synchrotron x-ray sources is crucial for both source characterization and coherent experimental techniques. Here, we present a method to probe the two-dimensional spatial complex coherence factor (CCF) of divergent x-ray beams without prerequisite source information. Phases of the divergent beams are obtained by the transport-of-intensity equation, which is indispensable for the retrieval of the CCF from the diffraction intensity of a Poisson-disk binary phase mask. Our method has been validated through simulations and is expected to be widely used in measuring coherence for fourth-generation synchrotron x-ray sources.

Polyvinylidene fluoride transducer shape optimization for the characterization of anisotropic materials.

In the context of ultrasonic determination of mechanical properties, it is common to use oblique incident waves to characterize fluid-immersed anisotropic samples. The lateral displacement of the ultrasonic field owing to leaky guided wave phenomena poses a challenge for data inversion because beam spreading is rarely well represented by plane wave models. In this study, a finite beam model based on the angular spectrum method was developed to estimate the influence of the transducer shape and position on the transmitted signals. Additionally, anisotropic solids were considered so that the beam skewing effect was contemplated. A small-emitter large-receiver configuration was chosen, and the ideal shape and position of the receiving transducer were obtained through a meta-heuristic optimization approach with the goal of achieving a measurement system that sufficiently resembles plane wave propagation. A polyvinylidene fluoride receiver was fabricated based on the findings and tested in three cases: a single-crystal silicon wafer, a lightly anisotropic stainless-steel plate, and a highly anisotropic composite plate. Good agreement was found between the measurements and the plane wave model.

Beam divergence errors in unbalanced laser interferometers – Case study with a free-fall absolute gravimeter FG5X

Beam divergence errors in unbalanced laser interferometers – Case study with a free-fall absolute gravimeter FG5X

Efficiency-enhanced TM-mode gyrotron with down-taper interaction structure

Recent advancements have shown that transverse magnetic (TM)-mode gyrotrons are feasible under specific conditions, yet their capabilities remain insufficiently explored. This article systematically investigates a W-band TM11-mode gyrotron within the down-tapered structure(s) to uncover its limitations and underlying physics. 2D interaction-efficiency maps are scanned as functions of the tube's geometrical parameters or beam parameters under magnetic-field tuning. An oversized tube integrated with short two-stage down tapers enhances the output efficiency of the fundamental axial mode and effectively alleviates the axial-mode competition. The peak electron-beam efficiency of the TM11 mode exceeds 50% with an idealized cold beam. The 3D particle-in-cell simulations are utilized to validate the real-time scheme including multiple transverse modes. Incorporating realistic beam spread, the first-harmonic TM11 mode effectively suppresses the second-harmonic and third-harmonic transverse electric modes with a maximum steady output of 130 kW, corresponding to an interaction efficiency of 37%. Complex dynamics regarding the mode-competing and mode-forming processes are revealed and discussed. This study not only facilitates the exploration of TM-mode gyrotrons but also provides insights into the harmonic gyrotron using the axis-encircling electron beam, where TM modes have more chances to be excited and dominate oscillations.

Ionization loss spectra of high-energy protons in an oriented crystal at various incidence angles with respect to a crystalline plane

The ionization energy loss distributions (spectra) of high-energy protons in oriented silicon crystals are considered on the basis of computer simulation. Evolution of the spectra with the change of the angle θ between the particle momentum and the crystal (110) plane is investigated. It is shown that both the most probable and the average energy loss change non-monotonically with the increase of θ. While at small θ these losses are lower than their values in a disoriented crystal, at larger θ they can be higher than these values. The dependence of the most probable energy loss on θ contains a discontinuity, which however might be challenging to register experimentally. Additionally, the influence of dechanneling and the incident beam divergence on the spectra of planar channeled protons is demonstrated.

200 mm optical synthetic aperture imaging over 120 meters distance via macroscopic Fourier ptychography

Fourier ptychography (FP) imaging, drawing on the idea of synthetic aperture, has been demonstrated as a potential approach for remote sub-diffraction-limited imaging. Nevertheless, the farthest imaging distance is still limited to around 10 m, even though there has been a significant improvement in macroscopic FP. The most severe issue in increasing the imaging distance is the field of view (FoV) limitation caused by far-field conditions for diffraction. Here, we propose to modify the Fourier far-field condition for rough reflective objects, aiming to overcome the small FoV limitation by using a divergent beam to illuminate objects. A joint optimization of pupil function and target image is utilized to attain the aberration-free image while estimating the pupil function simultaneously. Benefiting from the optimized reconstruction algorithm, which effectively expands the camera’s effective aperture, we experimentally implement several FP systems suited for imaging distances of 12 m, 65 m, and 120 m with the maximum synthetic aperture of 200 mm. The maximum synthetic aperture is thus improved by more than one order of magnitude of the state-of-the-art works from the furthest distance, with an over fourfold improvement in the resolution compared to a single aperture. Our findings demonstrate significant potential for advancing the field of macroscopic FP, propelling it into a new stage of development.

Near-infrared double-layer cascaded metasurface for beam shaping

The vast applicability of collimated flat-topped beam shapers, predominantly constructed from traditional lens elements, is met with challenges when the scale is less than wavelength. Metasurfaces have an excellent ability for optical manipulation, which can provide a promising approach to flat optics. Here, a metasurface-based Gaussian beam shaper is designed to combine the transmission phase principle with geometric transformation methods, which can reshape a 1550 nm Gaussian beam into a flat-topped beam with a uniformity of 84.39%. Furthermore, a cascaded metasurface beam shaper design is proposed to address the significant divergence in the flat-topped beam obtained from the single-layer metasurface. Simulation results indicate the output beam exhibits both uniform intensity and phase distributions over a considerable transmission distance, effectively minimizing the divergence of the output beam. This research has potential applications in various fields, such as optical antennas, fiber optics, and other optical systems.

Energy characteristics of the gridless ion sources beams

One of the most commonly used tools in ion-plasma technology is the End Hall ion source, which is used, in particular, for etching and other processes. The ability to operate on almost any gas, a highly divergent beam and the generated ions energy range up to several hundred electronvolts determine the wide possibilities of using End Hall ion sources in science and production. There are two main design schemes of such sources which are most actively used – with a floating and with an anode potential of the discharge chamber rear wall. The ion beam energy characteristics of the sources with a floating potential of the rear wall have been extensively studied by various research teams, but there is currently no comparable data available for sources with an anode potential, making it difficult to develop processes based on these ion sources. This study aims to investigate the energy characteristics of ions emitted from End Hall sources following these two design approaches. The ion beams were examined via a retarding potential analyzer. Measurements were conducted on argon at various discharge voltage and current settings for each source. One design included a floating potential of the discharge chamber rear wall, whereas the other design had an anode potential. The geometrical dimensions of the discharge chambers and the magnetic field intensities were identical for both configurations tested. Based on the ion beam retarding curves, corresponding ion energy distributions were determined. It was observed that for End Hall source with an anode potential of the discharge chamber rear wall an approximately continuous spectrum of ion energies was typical, whereas there was a clearly expressed peak in the energy distribution of the traditional configuration ion source beam. The mean ion energy in beam of the source with an anode potential of the discharge chamber rear wall was lower than that of the source with a floating potential, as confirmed by lower etch rates observed during control sputtering of stainless steel samples. These results can be used to develop technological procedures utilizing End Hall ion sources designed according to different configurations.

Simulation Study of High-Precision Characterization of MeV Electron Interactions for Advanced Nano-Imaging of Thick Biological Samples and Microchips.

The resolution of a mega-electron-volt scanning transmission electron microscope (MeV-STEM) is primarily governed by the properties of the incident electron beam and angular broadening effects that occur within thick biological samples and microchips. A precise understanding and mitigation of these constraints require detailed knowledge of beam emittance, aberrations in the STEM column optics, and energy-dependent elastic and inelastic critical angles of the materials being examined. This simulation study proposes a standardized experimental framework for comprehensively assessing beam intensity, divergence, and size at the sample exit. This framework aims to characterize electron-sample interactions, reconcile discrepancies among analytical models, and validate Monte Carlo (MC) simulations for enhanced predictive accuracy. Our numerical findings demonstrate that precise measurements of these parameters, especially angular broadening, are not only feasible but also essential for optimizing imaging resolution in thick biological samples and microchips. By utilizing an electron source with minimal emittance and tailored beam characteristics, along with amorphous ice and silicon samples as biological proxies and microchip materials, this research seeks to optimize electron beam energy by focusing on parameters to improve the resolution in MeV-STEM/TEM. This optimization is particularly crucial for in situ imaging of thick biological samples and for examining microchip defects with nanometer resolutions. Our ultimate goal is to develop a comprehensive mapping of the minimum electron energy required to achieve a nanoscale resolution, taking into account variations in sample thickness, composition, and imaging mode.

Verification of Angular Properties of a Divergent Pencil Beam of the Prometheus Therapeutic Facility

Verification of Angular Properties of a Divergent Pencil Beam of the Prometheus Therapeutic Facility

Experimental study on beam focusing of ionic liquid electrospray thruster with focus structure

The application of Ionic Liquid Electrospray Thrusters (ILETs) in micro/nanosatellites is very promising. However, the divergent beam of ILETs significantly affects their performance, including thrust, specific impulse, lifetime, propulsion efficiency, and more. Therefore, in order to improve the performance of ILETs, it is essential to optimize the beam. In this study, a focus structure was designed and fabricated. A series of beam focusing experiments were performed using a conical porous tungsten emitter and the ionic liquid EMI-BF4 as a propellant. The operational state of ILETs was demonstrated, with over 95 % of the beam composed of ions. After configuring the focus structure, the electric field in the emission region is weakened by the focus electrode, which has a certain negative effect on the starting voltage and emission current. Analysis of the beam focusing results showed that the focus structure reduced the beam divergence half-angle (half-angle) from 40° to 11° and concentrated the beam current within a half-angle of 7.3°. By estimating the thrust and specific impulse of the thruster, it was found that the focus structure could maximize the specific impulse by up to 22.4 % at the same voltage and increase it by approximately 23 % at the same power-to-thrust ratio. This focus structure demonstrated excellent focusing effect on a single conical emitter, making this research valuable as a reference for designing a focus structure for other types of emitters.

Dual-spherical-wave optical scanning holographic microscopy with resolution enhancement and an extended depth of field

Conventional optical scanning holographic microscopy (OSHM) is realized by using a plane wave and a spherical wave as the illumination. The resolution of the conventional OSHM is limited by the numerical aperture of the spherical wave and cannot exceed the Rayleigh limit. In this paper, the OSHM by using dual spherical waves as the illumination is studied. The model of a Gaussian wave, together with the constraints on the signal strength and the visibility, are considered in the analysis of the dual-spherical-wave (DS) OSHM. For an object located at the symmetry plane of the DS-OSHM, the resolution can slightly exceed the Rayleigh limit, and the depth of field (DoF) is extended significantly. For a transparent object, the noise in the DS-OSHM is less than that of the conventional OSHM, thanks to the highly divergent scanning beam. If the object is off the symmetry plane, the resolution is still enhanced, but the extension of the DoF is limited. In addition, a clear reconstructed image will be observed not only at the original object plane, but also at its mirror plane. To the best of our knowledge, this phenomenon is reported for the first time.

Semiconductor laser collimation and shaping design based on the combination of a rotationally symmetrical lens and a cylindrical lens

A dual-lens collimation and shaping system which is composed of a rotationally symmetric lens and an aspherical cylindrical lens is proposed in this paper. The system design method is discussed in detail, and the divergent elliptical laser beams are finally converted into collimated circular beams. The simulation results show that the maximum divergence angle of the beams can be collimated to 2.58 µrad, the standard deviation of the edge beam radius samples (SDRS) can be decreased from the original 4.227 to 0.135 mm, and the ratio of beam waist (RBW) drops from 1.554 to 1.0093 in the case of the output beam radius of 40 mm. The effects of transmission distance, astigmatism, wavelength deviation, light source offset, and lens offset on the collimation shaping effect are discussed. The collimation system can be widely used in long-distance optical communication systems and the design method in this paper can provide some new ideas for optical design researchers.

On the possibility of long‐distance transmission of OAM beam in rectangular tunnels

AbstractThis letter explores the possibility of long‐distance transmission of an orbital angular momentum (OAM) beam through rectangular tunnels. Theoretical analysis reveals that the OAM beam propagating in the tunnel with square cross section fulfills the conditions for axial propagation and exhibits azimuth symmetry. In comparison with free‐space OAM generation, we draw the conclusion that long‐distance transmission of OAM beams is achievable in the tunnels with square cross section. The validity of our conclusion is further substantiated through numerical experiments. Simulation results demonstrate that the first‐order OAM beam radiated by a uniform circular antenna array exhibits favorable helical phase distribution and the circular symmetry of the amplitude distribution in the tunnel beyond the Rayleigh distance. However, these characteristics degrade with increasing mode order and propagation distance, because the increase of high‐order OAM beam divergence angle and propagation distance will exacerbate the impact of multipath effects in the tunnel environment.

Adaptive Beam Divergence, and Intensity Decay Compensation in OCT for Enhanced Tissue Imaging

Adaptive Beam Divergence, and Intensity Decay Compensation in OCT for Enhanced Tissue Imaging

High birefringent slotted core slotted cladding porous core PCF for THz waveguide

A novel design featuring a porous core photonic crystal fiber (PC-PCF) is proposed in this paper for terahertz (THz) waveguide application. This work uses finite element method (FEM) and a boundary condition related to perfectly matched layer (PML) for analyzing the guiding properties. This methodology is supported by a fiber type featuring a slotted core and slotted cladding, utilizing Zeonex as the material. It offers high birefringence valued at 0.0978, small confinement loss of 10−14 dB/cm, a meager amount of effective material loss (EML) valued at 0.011697 dB/cm and a very high core power fraction (CPF) of 67.156%. Additionally, it shows a flattened pattern of dispersion measuring 0.4 ± 0.2 ps/THz/cm at an extensive frequency range of 0.5 THz to 2 THz. Other significant waveguide properties: effective refractive index, numerical aperture (NA), V-parameter, effective area, spot size, and beam divergence of the suggested fiber are numerically analyzed and conferred thoroughly. Regarding its mode of operation, the proposed fiber primarily functions in multimode, but it can also operate in single mode for higher porosity levels and lower core diameters. This unique characteristic renders the proposed PC-PCF structure well-suited for a broad range of applications, offering versatility as to its mode of operation.