Beam Symmetry Research Articles

Symmetry of polychromatic beams and transverse energy flows

The article considers the mechanisms of the formation of transverse energy flows in polychromatic fields with different structures. It is shown that the magnitude of the Poynting vector transverse component and the angular momentum for symmetric polychromatic beams are the same as in coherent monochromatic fields. Changes in the characteristics of energy flows due to the transformation and destruction of beam symmetry are demonstrated. The data of computer simulation are presented.

Electron Beams Commissioning and Initial Measurements on an Elekta Synergy Platform Linear Accelerator

A linear accelerator (Linac) must be commissioned for use in treating cancer patients. This research work aims to analyze part of the electron beam data produced by the Elekta Synergy Platform Linac at the radiotherapy department at Tripoli University Hospital, Tripoli, Libya. In this paper, percentage depth dose (PDD), beam profile and applicators factor were studied at five different electron beam energies (4, 6, 8, 10 and 12 MeV). The relative measurement part of this study was carried out using a PTW MP3-M 3D water scanning system, and the absolute measurement was taken using a plane parallel ionization chamber and a unidose E electrometer. The analysis for these measurements has yielded the following results: a) The Penetrative qualities of all the electron beam energies were within the manufacturer's tolerance limits of ±1%; b) the maximum values of beam flatness of 2.94 and beam symmetry of 1.93 are within the accepted limits of International Electrotechnical Commission criteria; c) A penumbra maximum value of 1.30 was measured at the 4-MeV electron beam energy and using a 14×14 cm2 applicator size. All the obtained parameters were within the permissible limits. Therefore, the electron beams can be safely used for clinical purposes.

Wire antenna with skew planar wheel structure for generating high‐purity OAM beam

AbstractThis paper presents the generation of an orbital angular momentum (OAM) wave using a wire antenna with a skew planar wheel structure at 5.8 GHz. The wire antenna consists of four arms, each of which behaves like a left‐handed circularly polarized antenna. The orientation and rotation of each arm are adjusted to obtain the desired phase shift, resulting in the generation of an OAM wave. The proposed design is fabricated and tested, and the results demonstrate that the OAM beam produced has high mode purity, with a peak gain of 2.8 dBi, divergence angle of , and high azimuthal symmetry. Both simulated and measured results confirm the effectiveness of the proposed wire antenna in generating an OAM wave. The proposed wire antenna has a wide range of potential applications, including communication systems, remote sensing, and radar imaging. In particular, the azimuthal symmetry of the OAM beam makes it particularly suitable for unmanned aerial vehicle applications.

Kernel Density Estimators for Axisymmetric Particle Beams

Bright beams are commonly represented by sampled data in the numerical algorithms used to simulate their properties. However, in these calculations and the analyses of their outputs, the beam’s density is sometimes required and must be calculated from the samples. Axisymmetric beams, which possess a rotational symmetry and are naturally expressed in polar coordinates, pose a particular challenge to density estimators. The area element in polar coordinates shrinks as the radius becomes small, and weighting the samples to account for their reduced frequency may cause unwelcome artifacts. In this work, we derive analytical expressions for two kernel density estimators, which solve these problems in the spatial coordinates and in the transverse phase space. We show how the kernels can be found by averaging the Gaussian kernel in Cartesian coordinates over the polar angle and demonstrate their use on test problems. These results show that particle beam symmetries can be taken advantage of in density estimation while avoiding artifacts.

High-resolution reconstruction of spectrum-overlapped off-axis holography by deflecting reference beam of Gaussian symmetry

In digital holography, extracting the +1-order spectrum accurately and making full utilization of the spatial bandwidth of the CCD sensor are essential for high-resolution and artifacts-free quantitative phase imaging. In this paper, using the light intensity symmetry of the Gaussian laser beam, we delicately eliminate the zero-order spectrum by means of subtraction of two off-axis hologram spectra acquired by symmetrically deflecting the reference beam. Therefore, the +1-order spectrum can be extracted accurately even if it is completely overlapped with the zero-order spectrum. Compared with phase-shifting methods, such as pi-phase and random phase, which require accurate control or calculation of the phase-shifting amount, this proposed method does not need to precisely control the deflection angle of reference beam. Being achievable the maximum utilization of half-space bandwidth of the CCD sensor, the proposed method has realized high-resolution imaging demonstrated by the experimental results of three specimens. This method has general applications in digital holography, such as eliminating the zero-order spectrum and extracting the +1-order spectrum.

Vortex-antivortex pair control in quadrupole Gaussian beams.

A multi-vortex system nested in a Gaussian beam forms complex paths when it propagates in a free space. We consider a configuration of vortex quadrupole and present a systematic way to control the creation and annihilation of vortex pairs using only one parameter. It is shown that three classes of quadrupole vortex beams can be identified by the number of vortex pairs created or annihilated. The beam symmetry, asymptotic behavior, and stability are analyzed. The main theoretical results are verified experimentally.

Ray Tracing Simulation of X-ray Microdiffraction Beamline on the Inverse Compton Source

This paper deals with the simulation of output beam parameters of the inverse Compton X-ray Source (ICS). The simulation takes into account the main parameters of the laser and electron beams, such as their pulse shapes, polarization properties as well as the angular and energy dispersion of the electrons. The layout of the presented ICS and X-ray optical beamline is dedicated to X-ray micro-diffraction studies. To maintain the axial symmetry of output X-ray beams at different photon energies, the beamline monochromator is based on a single crystal installed in the Borrmann transparency condition.

Beam dynamics optimization in the LEBT of LLICTF

A Low Energy Beam Transport (LEBT) has been designed and optimized to inject both a 50[Formula: see text]keV/u, 50[Formula: see text]mA [Formula: see text] beam and a 20[Formula: see text]keV/u, 1[Formula: see text]mA [Formula: see text] beam into the downstream Radio Frequency Quadrupole (RFQ) at the Lanzhou Light Ion Cancer Therapy Facility (LLICTF). The overall aim is to increase the operation efficiency and simplify the complexity of the LLICTF. This dual-beam operation mode creates phase space distortions as a result of the intense space charge, and causes transverse asymmetry due to a mixture of solenoids and a dipole magnet. To mitigate the phase space distortions of the high-intensity proton beam, two beam scrapers have been placed at locations determined through careful analysis of the space charge forces and external focusing force of the beam. Additionally, the Particle Swarm Optimization (PSO) algorithm has been utilized to obtain an approximate solution for the dipole parameters, which helps maintain the symmetry of different symmetrical beams passing through it. Optics designs that implement these solutions are verified with multi-particle simulations.

Development of seven-beam optics using dielectric lenses for a new 72–116 GHz receiver in the Nobeyama 45 m telescope

Abstract We developed a new seven-beam heterodyne receiver “7BEE” in the 72–116 GHz band for the Nobeyama 45 m telescope to investigate the early stage of star formation by deriving the deuterium fraction of dense cores. The optics for the receiver employs wideband corrugated horns covering the 72–116 GHz band and dielectric lenses to couple the incoming radiation from the antenna on to the feeds. One of the important aspects in the lens design is the anti-reflection (AR) structure to mitigate the reflections on the lens surfaces. Triangular grooves, which gradually change the effective refractive index from air to dielectric, were adopted as a basic AR design since the return loss can be in the order of 20 dB or better. The main goal of this study is to compare the radio frequency (RF) characteristics of the lenses with different patterns and sizes of AR grooving structures. We confirmed that concentric grooves degraded beam symmetry, cross-polarization characteristics, and aperture efficiency due to the birefringence of the grooves, which gave rise to wavefront distortions. Straight grooves of two different gap widths, 1.2 mm and 1.7 mm, were compared and showed similar good performance in terms of beam patterns and noise contribution. However, the latter showed a few percent higher aperture efficiency. Therefore, the straight grooves with 1.7 mm gap width were adopted as the AR structure of our lens.

Dosimetric Analysis of Rhizophora-based Phantom Material in Radiation Therapy Applications Using Monte Carlo GATE Simulation.

This study aims to determine the percentage depth dose (PDD) of a phantom material made from soy-lignin bonded Rhizophora spp. particleboard coated with a gloss finish by using Monte Carlo Geant4 Application for Tomographic Emission (GATE) simulation. The particleboard was fabricated using a hot pressing technique at target density of 1.0 g·cm-3 and the elemental fraction was recorded for the simulation. The PDD was simulated in the GATE simulation using the linear accelerator Elekta Synergy model for the water phantom and Rhizophora phantom, and the results were compared with the experimental PDD performed by several studies. Beam flatness and beam symmetry were also measured in this study. The simulated PDD for Rhizophora and water was in agreement with the experimental PDD of water with overall discrepancies of 0% to 8.7% at depth ranging from 1.0 to 15.0 cm. In the GATE simulation, all the points passed the clinical 3%/3 mm criterion in comparison with water, with the final percentage of 2.34% for Rhizophora phantom and 2.49% for the water phantom simulated in GATE. Both the symmetries are all within the range of an acceptable value of 2.0% according to the recommendation, with the beam symmetry of the water phantom and Rhizophora phantom at 0.58% and 0.28%, respectively. The findings of this study provide the necessary foundation to confidently use the phantom for radiotherapy purposes, especially in treatment planning.

Effect of Diode-Based Transmission Detector Measurement on Dose Perturbation during Delivery of 6MV Photon

<h3>Purpose/Objective(s)</h3> Delivery dose quality assurance (QA) during treatment planning execution is the most direct and effective way to ensure that the prescribed dose is delivered accurately and the patient is irradiated safely. The purpose of this article is to evaluate the stability and sensitivity of the diode-based transmission detector (TD) installed on the beam path during radiotherapy, and analyze the effect of TD on the photon beam fluence and dose distribution. <h3>Materials/Methods</h3> The beam fluence with and without TD was measured for 6MV on a linear accelerator. The point doses at different depths (0.0cm∼15.0cm), different dose values (100MU∼500MU), different dose rates (100MU/min∼600MU/min) and different irradiation fields (3cm × 3cm∼20cm × 20cm) were measured by cylindrical three-dimensional water tank, and the transmission factors (TF) were calculated and analyzed. The percentage depth dose (PDD) and beam profile under different parameters were collected to analyze the effect of TD on ray quality and dose distribution. The effect of different irradiation fields on the γ passing rate was evaluated by a planar dosimeter. <h3>Results</h3> The diode-based TD has the high stability of 0.1% (1SD) and excellent position monitoring performance (≤0.2mm). The TF varies with the depth, dose, dose rate and irradiation fields. When the depth is 0cm, the TF has maximum value of 99.55%. For the depth of 0cm∼5cm, the TF increases with the increase of dose and dose rate (<i>R</i>=0.91, 0.75). For the depth of 5cm, the TF is least affected by dose and dose rate (1SD: 0.01%, 0.07%), and decreased with the increase of irradiation fields, 98.94% for 3cm × 3cm. When the depth is >5cm, it decreases with the dose increasing (<i>R</i>=−0.88∼−0.26), and increases with the dose rate increasing (<i>R</i>=0.78). The average TF under all the above conditions is 98.46%, that is, beam attenuation is 1.54%. The movement of the position of maximum dose depth is 0.124cm for 5cm × 5cm and 0.250cm for 3cm × 3cm to the surface of the water (0cm), otherwise ≤0.003cm. TD increases dose in build-up region, 1.49% for fields of 20cm × 20cm. TD effects ray quality (≤0.0028), beam symmetry and flatness (≤0.68%). The γ passing rate does not change under the commonly used indexes of 3%/3mm and 2%/2mm. <h3>Conclusion</h3> The diode-based TD has high stability and excellent monitoring performance. Although it has little effect on ray quality, beam symmetry, flatness and γ passing rate, it will cause beam attenuation and increase surface dose.

Synthesis of Difference Patterns for 3-D Conformal Beam-Scanning Arrays With Asymmetric Radiation Aperture

Due to the asymmetry of the elements’ position distribution and polarization direction, it is a challenge to synthesize difference patterns with large slope and symmetric main-lobe on 3-D conformal beam-scanning arrays with asymmetric radiation aperture. In this article, an approach to synthesize the optimal difference patterns for 3-D conformal arrays with asymmetric radiation aperture is proposed. To determine the limitation region of the main-lobe and sidelobe for a 3-D conformal array, an initial difference pattern is generated by the joint multidimensional vector clustering method. Then, an auxiliary phase function is introduced to convert the nonconvex constraint of the symmetry of the difference beam into a convex one. Finally, an iterative convex optimization is applied to obtain the optimal difference pattern. The optimization progress is finished by extracting the vector field patterns of a simulated antenna element. Two design examples employing hemispherical conformal array (HCA) and conical conformal array (CCA) with asymmetric radiation aperture are implemented to demonstrate the effectiveness of the proposed method. Difference patterns with −20 dB sidelobe level (SLL) and large slope are obtained in both numerical and simulated results of the two design examples.

The LSPE-Strip beams

In this paper we describe the design and characterization of the optical system of LSPE/Strip, a coherent polarimeter array that will observe the microwave sky from the Teide Observatory in Tenerife in two frequency bands centred at 43 and 95 GHz through a dual-reflector crossed-Dragone telescope of 1.5 m aperture. In general, optical systems composed by a telescope-feed array assembly have non-idealities that might limit their ability to perform high-precision measurements. It is thus necessary to understand, characterize and properly control these systematic effects. For this reason, we performed electromagnetic simulations to characterize angular resolution, sidelobes, main beam symmetry, polarization purity and feedhorns orientation. The results presented in this paper will be an essential input for further optical studies and for the LSPE/Strip data analysis. Ultimately, they will be used to assess the impact of optical systematic effects on the scientific results.

Development of a 70–110 GHz silicon corrugated horn for cosmic microwave background experiment

Next generation cosmic microwave background (CMB) polarization telescope will use large arrays of receiver with nearly 100 000 transition edge sensor (TES) detectors and receiving antennas. Such large TES and antenna array is a big challenge for the fabrication of TES and antennas. A 35-layers silicon-platelet corrugated horn for 70–110 GHz is designed and fabricated based on the micro electro mechanical system (MEMS) technology. Compared with the traditional corrugated horn, the last layer of the 35-layers silicon-platelet is designed with no corrugation to increase the beam symmetry. A parametric HFSS model of the horn was established to evaluate the performance of the horn and effect of fabrication process. The measured S11 and cross-polarization of the fabricated prototype horn are both below −20 dB while the sidelobe at 70 and 90 GHz is below −20 dB. The beam symmetry of the horn is good in 70–110 GHz band. The measured gain is greater than 15 dBi. These results show that the performance of the designed horn meets the requirement of CMB experiment.

Method for evaluating the polarization performance of cylindrical vector polarized beams

Cylindrical vector polarized (CVP) beams are widely used in many applications due to their special polarized distribution and highly focused properties. It is crucial to evaluate the polarization performance of CVP beams. This paper proposes several polarization parameters for comprehensively evaluating the overall polarization performance and spatial polarization symmetry of CVP beams. To verify this method, several different CVP beams are simulated, and the polarization performance of these beams are indicated. In addition, the trapping models are built to compare trapping capacities of the beams with different polarization performance. The results indicate that the ideal CVP beams demonstrated a higher trapping force than the non-ideal ones, and the trapping force was sensitive to the spatial polarization symmetry of the beams. This evaluation method plays an important role in applications that are susceptible to the polarization performance of the beams.

Rotation and Revolution of Optically Trapped Gold Nanorods Induced by the Spin and Orbital Angular Momentum of a Laguerre–Gaussian Vortex Beam

AbstractOptical trapping, spinning, and orbiting of nanoparticles allow the study of nanoscale mechanical, thermal, and optical effects. A circularly polarized Laguerre–Gaussian beam can simultaneously rotate a gold nanorod about its symmetry axis while revolving it around the beam's symmetry axis. The first motion is rotational in character, whereas the second is translational. Effective temperatures of each motion are experimentally obtained and compared with predictions from the Hot Brownian Motion theory. The results also show the optical‐to‐mechanical torque‐transduction efficiency to be equal for the spin and orbital angular momentum.

Three-dimensional spiral motion of microparticles by a binary-phase logarithmic-spiral zone plate.

Acoustic vortex beams, which have both linear and angular momentum, can be used to make precise acoustic tweezers. Limited by the symmetry of a normal vortex beam, these tweezers are usually used for trapping or rotating particles in two dimensions. Here, the three-dimensional spiral motion of two soft particles of different sizes was realized using a vortex beam with a twisted focus, which was synthesized by a silicone binary-phase logarithmic-spiral zone plate. Numerical simulations and experimental measurements demonstrated that the beam had anisotropic focuses of crescent transverse intensity profiles and a screw phase dislocation with a singularity at the center. Experiments showed that a small particle (k0r ≈ 1.3) can follow the twisted intensity of the beam, but a large particle (k0r ≈ 4.7) spirals up away from the twisted field pattern. This is attributed to the dominant gradient force for the small particle, whereas the scattering effect induced a scattering force combined with a gradient force for the large particle. This focused twisted beam, which was generated with a structured silicone plate, and the three-dimensional spiral motion of microparticles, advance the development of simple, compact, and disposable acoustic devices for the precise and diverse manipulation of microparticles.

On the rotation repetitions of Mathieu beams angular spectrum in frequency space

In the recent works on Mathieu beams, the angular spectrums commonly used are even and odd angular Mathieu functions with an angular variation vary between 0 to 2π. In this work, we propose to introduce a new index m characterizing the rotation repetitions (m-times) of the structure of the original angular spectrum of Mathieu beams on the total circle in the frequency space. With this index, the angular spectrum of Mathieu beams rotation can be controlled to change the beam symmetry. We study the effect of these repetitions of the angular spectrum on the even and odd Mathieu modes features when they propagate through a paraxial optical system. We show that rotated repetitions of the angular spectrum does not affect the nondiffracting property of the beams. To illustrate the rotation repetitions of the angular spectrum, the Fourier transform of the beam is calculated in the focal plane of a thin lens. From the obtained results, we can conclude that the rotation repetitions of the angular spectrum can be used to produce others Mathieu beams shapes and can enrich the applications of these kinds of beams.

Optical tunnels: long-range optical trapping and manipulation in aqueous media

In this study, we demonstrate an asymmetric counter-propagating beam system with engineered optical forces allowing for long-range particle trapping and manipulation. We achieved this by breaking the symmetry of the well-known counter-propagating optical trapping beams. By doing so, we extend the range of optical forces for particle confinement and transportation to significantly larger foci separations, creating an optical tunnel. These tunnels are capable of moving matter forward and back with controllable speeds for more than a millimeter length with the ability to bring them to a full stop at any point, creating a stable 3D trap. Our trap stiffness measurements for the asymmetric trapping system demonstrate at least one order of magnitude larger values with respect to the symmetric counter-propagating beams so far reported. Our system is quite versatile as it allows for single or multi trapping with flexible positioning of any size particle ranging from tens of nanometers to tens of microns with powers as low as a few milliwatts.

Improving security in terahertz wireless links using beam symmetry of vortex and Gaussian beams.

We present an effective way to improve the security of a point-to-point terahertz wireless link on a physical layer supported by numerical calculations in the frame of Fourier optics. The improvement is based on original countermeasures which exploit three independent degrees of freedom of the carrier wave: its intensity and azimuthal and radial symmetry. When the transmission line is intercepted, the light beam is subject to changes in either of the three degrees of freedom. We propose a strategy to measure these changes and they are quantified by a single eavesdropping parameter that is shown to be correlated to the secrecy capacity of the transmission. Consequently, its excessive value serves as an indication of the beam interception. We consider the carrier wave in the form of Gaussian and vortex beams. Comparison between the two reveals that vortex beam ensures a even higher level of security.