Helical Beam Research Articles

Measuring the OAM spectrum of a fractional helical beam in a single shot

Measuring the OAM spectrum of a fractional helical beam in a single shot

Helical Micropillar Processed by One-Step 3D Printing for Solar Thermal Conversion.

Solar thermal utilization has broad applications in a variety of fields. Currently, maximizing the photo-thermal conversion efficiency remains a research hotspot in this field. The exquisite plant structures in nature have greatly inspired human structural design across many domains. In this work, inspired by the photosynthesis of helical grass, a HM type solar absorber made in graphene-based composite sheets is used for solar thermal conversion. The unique design promoted more effective solar energy into thermal energy through multiple reflections and scattering of solar photons. Notably, the Helical Micropillar (HM) is fabricated using a one-step projection 3D printing process based on a special 3D helical beam. As a result, the solar absorber's absorbance value can reach 0.83 in the 400-2500nm range, and the surface temperature increased by ≈128.3% relative to the original temperature. The temperature rise rate of the solar absorber reached 22.4°Cmin-1, demonstrating the significant potential of the HM in practical applications of solar thermal energy collection and utilization.

Direct determination of topological charge of structured light via phase-shift interference

We present a straightforward theoretical approach for the direct observation of the orbital angular momentum (OAM) charge inherent in structured light. Our method involves utilizing phase-shift interference of beams to discern the sign and magnitude of the topological charge associated with Laguerre–Gaussian (LG) beams. Specifically, we demonstrate that the topological charge of an LG beam can be ascertained through the interference with a corresponding helical wavefront beam possessing an opposite charge due to the reflection in Mach–Zehnder-like interferometer. The determination of the topological charge magnitude is facilitated by examining the interference pattern’s half number of petals. Additionally, our study reveals that the petal-like interference pattern undergoes azimuthal shift, with the direction of rotation being contingent upon the sign of the topological charge of the beam. Notably, for a negative phase shift, a anti-clockwise azimuthal shift corresponds to a positive topological charge, while an clockwise rotation is associated with a negative topological charge. This work contributes to the advancement of methods for characterizing structured light based on OAM charge, with potential applications in diverse fields such as optics, telecommunications and topological photonics.

Analysis of Spatial Curved Bi-Fixed Beam with Varying Curvature and Varying Cross-Sectional Area Using Finite Displacement Transfer Method

This article is focused on determination of fixed-end reactions, displacements, internal forces and internal moments for the spatial curved bi-fixed beam with varying curvature and varying cross-sectional area. The objective is to analyze spatially curved beam without involving analytical differentiation and integration of the governing equations. A finite displacement transfer method to analyze spatially curved beam is used to obtain numerically approximate analysis results and to eliminate analytical differentiation and integration, completely. The results of the analysis procedure are compared with the results of other methods found in the literature. For the specific case of the circular helical beam, the fixed end reactions' values have absolute maximum and minimum percentage differences of 1.23% and 0.06%, respectively. For the specific case of the elliptic-helical beam, the fixed end reactions' values have absolute maximum and minimum percentage differences of 1.13% and 0.0%, respectively. The finite difference method, along with the recursive scheme, gives reasonably accurate results without involving complex calculations

Generation of multi-freedom controllable helical beam through high-order Bessel beams [Invited

Generation of multi-freedom controllable helical beam through high-order Bessel beams [Invited

Chirped LG modes interference formed chiral beams

Non-Gaussian spatial intensity distribution beams used in laser micro- and nano-machining find many applications. For instance, Bessel beams, having a small diameter and a very long focal zone, allow the fabrication of high aspect ratio modifications in transparent materials. Higher-order Laguerre–Gauss modes are used in particle manipulation and even for multiplexing in optical communication. The temporal intensity distribution of a pulse is mostly overlooked or fixed to Gaussian shape distribution. However, pulse-shaped beams could improve the same fields of particle manipulation as optical traps, or the laser manufacturing. In this paper, we demonstrate a method of constructing a helical spatiotemporal intensity distribution beam the rotation of which in time can be varied. We demonstrate the analytical and numerical results and show an experimental realization of such a structure.

Исследование усталостной долговечности пружин боковых скользунов тележки модели 18-9891

Purpose: To conduct comprehensive experimental studies on the fatigue strength of side bearing springs for freight bogies, evaluating the effectiveness of thermal and shot peening treatments during their manufacturing process. Methods: The method of stand endurance (fatigue) testing of constant contact side bearing springs has been applied, allowing for obtaining endurance characteristics of actual components. Metallographic studies of spring steel have been conducted to investigate the influence of strengthening operations during spring manufacturing on their fatigue strength, with the assessment of mechanical characteristics of surface layers in various zones of the helical spatial beam. Results: Experimental force characteristics of spring sets for side bearings of an innovative freight bogie with a load of 25 tons (245 kN) on the axle have been obtained. Fatigue curves of the springs have been presented in a probabilistic aspect, enabling the determination of load factor for fatigue strength of the springs considering operational loading, as well as justifying the compliance of the spring sets with the regulatory requirements. Practical significance: Based on the research results, the considered constructive-technological variant of the constant contact side bearing spring for the freight bogie has been put into serial production. The test results allow us to reasonably determine the warranty mileage of the responsible assembly of the bogie and to conduct further work on the design modernization with the aim of increasing operational life.

Phase shifting to measure the modal composition of the scattered helical beam

We propose and experimentally demonstrate a non-interferometric and highly stable technique to recover the incident orbital angular momentum (OAM) modes from the randomly scattered coherent light. To implement and demonstrate this technique, a non-separable state is generated by encoding spiral and non-spiral modes into the orthogonal polarization bases prior to propagation through a random scattering media. Recovery of the complex OAM mode of the incident light becomes possible by quantitatively measuring the complex Fourier coefficients from the polarization correlation of the random light field along with the three-step phase-shifting method. A detailed theoretical basis of the proposed method is presented and verified by numerical simulation and experimental tests.

Role of Multidetector Computed Tomography in the Evaluation of Maxillofacial Trauma.

Maxillofacial fractures are among the commonest injuries occurring in trauma patients. Multislice computed tomography (CT) is a widely used radiological investigation that accurately reveals the number, location, and extent of the fractures as well as concomitant soft tissue injuries and has been found to be superior in the diagnosis of maxillofacial fractures owing to high sensitivity and specificity. This study was performed to assess the efficacy of axial, coronal, sagittal, and three-dimensional (3D) reformatted images in the detection of fractures in maxillofacial trauma. This was a cross-sectional descriptive study conducted on 49 adult patients with maxillofacial injuries undergoing multislice CT using a multidetector SiemensSOMATOM Emotion eco 16 slice CT scanner (Siemens AG, Munich, Germany). CT protocol consisted of non-contrast axial 16-slice helical series beam collimation ~ 3 mm, pitch ~ 0.8 - 1, tube current ~ 270 mAs, voltage ~ 130 kV, Total exposure time ~ 18 seconds, total radiation ~ 200 mGy. Along with the axial, coronal and sagittal images were reconstructed with 0.5 mm increment. 3D volume-rendering images were also obtained. 3D images were compared with axial images, coronal and sagittal plane images. The maximum number of cases was in the age group of 21-30 years with the male: female ratio being 5.12:1. The most common cause of injury was road traffic accidents (RTA). Mandible fractures were found to be the most common (20 patients, 40.8%) followed by fractures of nasal bone (18 patients, 36.7%). The incidence of frontal bone fractures was found to be the least(six patients, 12.24%). Our study found that 3D images are superior to axial in assessing the extent and degree of displacement of maxillofacial fractures in general. The maxillary sinus was found to be the most commonly fractured sinus (19 patients, 38.7%). Sphenoid sinus fractures were the least common (seen in two patients, 4.08%). CT findings correlated with the operative findings in most types of fractures. Multidetector CT with multiplanar and 3D reformation is highly accurate in the identification of fractures and assessing the extent and degree of displacement of fractures; hence, it is the imaging modality of choice in maxillofacial trauma.3D images are much better for the detection of maxillofacial fracturescompared to axial, coronal, or sagittal views, especially in maxilla and mandibular bone fractures. It is also found to be betterat providing information on thepatterns of the fracture lines and the displacement of the fracture fragments. Another added advantage of multidetector CT is that it is a non-invasive technique with good accuracy and a short scan time.

Zernike-coefficient extraction via helical beam reconstruction for optimization (ZEHBRO) in the far field

Abstract The spatial distribution of beams with orbital angular momentum in the far field is known to be extremely sensitive to angular aberrations, such as astigmatism, coma and trefoil. This poses a challenge for conventional beam optimization strategies when a homogeneous ring intensity is required for an application. We developed a novel approach for estimating the Zernike coefficients of low-order angular aberrations in the near field based solely on the analysis of the ring deformations in the far field. A fast, iterative reconstruction of the focal ring recreates the deformations and provides insight into the wavefront deformations in the near field without relying on conventional phase retrieval approaches. The output of our algorithm can be used to optimize the focal ring, as demonstrated experimentally at the 100 TW beamline at the Extreme Light Infrastructure - Nuclear Physics facility.

Stokes correlation to estimate topological charge from the speckle pattern

The orbital angular momentum (OAM) of the vortex or helical beam, connected with the topological charge (TC) of the beam, has been used as an alternative degree of freedom to encode and decode the information in the optical signals. Many detection schemes have been established to determine the TC configurations and decode the information at the receiver end of the encoded information from the transmitter end for the free space. However, when the helical beam is transmitted through the scattering medium, its wavefront is spatially scrambled without any direct information about the incident helical beam. Here, we propose and experimentally demonstrate a new approach to estimate the TC of the helical beam from the non-imaged randomly scattered pattern. The technique utilizes Stokes parameters (SPs) of the random field to evaluate higher-order SPs fluctuation correlation. A complete theoretical model of the technique is presented and verified with numerical simulation and experimental tests. A good agreement is found between the simulation and experimental results.

A review on acoustic vortices: Generation, characterization, applications and perspectives

Acoustic vortices provide a single-beam approach to manipulate objects with sizes from nanometers to millimeters, gaining increasing interest in recent years. The helical beam renders them good ability to trap particles in three dimensions stably. At the same time, the orbital angular momentum of acoustic vortices can be used to realize object rotation and data transmission. In this review, we summarize the generation and characterization of acoustic vortices. Furthermore, we present the application of acoustic vortices in particle manipulation, object rotation, acoustic communication, and especially in the biomedical field. Finally, perspectives on the future directions for acoustic vortex research are discussed.

Irradiation Methods for Accurate Dose Delivery to Postoperative Keloid Scars With Minimal Normal Tissue Exposure Using TomoTherapy: A Phantom Study.

We aimed to clarify the TomoTherapy irradiation method for accurate dose delivery to the postoperative ear keloid with minimal exposure. An electron beam of Elekta synergy and static and helical photon beams of TomoTherapy were delivered to the auricle and lobe of an anthropomorphic phantom compensated using a soft rubber bolus. The doses to the ear surface and the eyeballs and thyroid were measured using radiochromic film and glass dosimeters, respectively. Using static, helical, and electron beams, the respective doses to the ear surface were 97.9%, 103.0%, and 91.7% of the prescribed dose; the respective doses to the thyroid were 0.6, 0.8, and 2.4 cGy; the respective doses to the left eyeball were 3.3, 6.9, and 2.7 cGy. The static beam of the TomoTherapy can be safely used for treating ear keloids, while ensuring target dose. The helical photon beam spreads out the low-dose exposure.

Use of a novel helical fan beam imaging system for computed tomography of the head and neck in sedated standing horses: 120 cases (2019-2020).

To evaluate the diagnostic capabilities of a novel helical fan beam CT system used for imaging of horses with clinical problems of the head and neck. 120 horses. Medical records were reviewed of horses presented for CT of the head or neck at 2 university hospitals. The following data were recorded: age, sex, breed, presenting complaint, sedation used for imaging, scanning time, procedure time, other diagnostic imaging methods performed, imaging diagnosis, clinical diagnosis, and complications during imaging. Quarter Horses and Warmbloods were the most common breeds, and the most common complaint was nasal discharge. The head (101/120 [84%] horses) was scanned most frequently, and the most common diagnoses were primary dental disease and a space-occupying lesion of the paranasal sinuses. Nuchal bursitis was the most common imaging diagnosis in the neck region. Procedure time ranged from 20 to 45 minutes with a scanning time of 30 to 40 seconds. No complications with horse sedation occurred, and horses tolerated scanning well. An imaging diagnosis was more frequently achieved with CT (109/120 [91%] horses) than with planar digital radiography (23/61 [38%] horses). The helical fan beam CT system had fast scanning times and could be used safely for routine imaging of the teeth and sinuses in horses. The caudal extent of scanning in the neck region was limited by the shape of the horse's neck and thorax.

Use of a novel helical fan beam imaging system for computed tomography of the distal limb in sedated standing horses: 167 cases (2019-2020).

To evaluate the diagnostic capabilities of a novel helical fan beam CT system used for imaging of horses with a range of clinical distal limb problems. 167 horses. Medical records were reviewed of horses presented for CT of the distal limb at 2 university-based veterinary hospitals. The following data were recorded: age, sex, breed, presenting complaint, sedation used for imaging, scanning time, procedure time, other diagnostic imaging methods performed, imaging diagnosis, clinical diagnosis, and complications during imaging. Most horses were Thoroughbreds and Quarter Horses. Procedure times ranged from 15 to 40 minutes, with scanning completed in 15 to 45 seconds for each region of interest. The foot or pastern region was commonly scanned (88/167 [53%] horses), with navicular bone disease diagnosed in 42 of 88 (48%) horses. The fetlock region was also commonly scanned (42/167 [40%] horses), with palmar or plantar osteochondral disease diagnosed in 17 of 42 (40%) horses. Horses were compliant during scanning, and no complications with sedation or damage to the scanner occurred. A specific imaging diagnosis for the lameness was achieved more frequently with CT imaging (166/167 [99%]) than with planar digital radiography (26/58 [45%]). The helical fan beam CT system could be used safely to scan sedated standing horses from the carpal or tarsal region distally. Subjectively, the machine was easy to operate, allowing CT to be incorporated into lameness investigations. CT imaging was very likely to result in a clinical diagnosis in horses with distal limb lameness.

Differentiated transmittance of vortex beams in helical polymer media

Light beam with helical wavefront, also called optical vortex, carries quantized orbital angular momentum, and as such have many potential photonic applications. In this study, the interaction of a fluorene-based helical polymer thin film with vortex beams was studied. The helicity of the polymeric strands was greatly enhanced by thermal annealing. A liquid crystal phase plate was used to convert TEM00 laser beams into a helical wavefront beam with a phase singularity at its axis. A relatively high absorption dissymmetry was observed in a longer wavelength range, compared with the linear optical absorption of the annealed film sample. The left- and right-handed vortices had different transmittances. The absorption asymmetry of the annealed fluorene film in the case of vortex beams is mainly attributed to quadrupole interactions.

Electron acceleration from transparent targets irradiated by ultra-intense helical laser beams

The concept of electron acceleration by a laser beam in vacuum is attractive due to its seeming simplicity, but its implementation has been elusive, as it requires efficient electron injection into the beam and a mechanism for counteracting transverse expulsion. Electron injection during laser reflection off a plasma mirror is a promising mechanism, but it is sensitive to the plasma density gradient that is hard to control. We get around this sensitivity by utilizing volumetric injection that takes place when a helical laser beam traverses a low-density target. The electron retention is achieved by choosing the helicity, such that the transverse field profiles are hollow while the longitudinal fields are peaked on central axis. We demonstrate using three-dimensional simulations that a 3 PW helical laser can generate a 50 pC low-divergence electron beam with a maximum energy of 1.5 GeV. The unique features of the beam are short acceleration distance (∼100 μm), compact transverse size, high areal density, and electron bunching (∼100 as bunch duration).

Calibration of nonlocal generalized helical beam model for free vibration analysis of coiled carbon nanotubes via molecular dynamics simulations

This paper studied the free vibration behavior of coiled carbon nanotubes (CCNTs) using continuum mechanics methods and molecular dynamics (MD) simulations. Based on the continuum mechanics method, a new elasticity model called the nonlocal generalized Washizu beam (NGWB) was innovated by considering the effects of the curvature and cross-section thickness of nanotubes, as well as size-dependent effect. Then, the governing equations for the vibrational behavior of CCNTs were derived and solved using the numerical generalized differential quadrature method (GDQM). The free vibration behavior of CCNTs was also examined by performing the MD simulations to determine the calibrated values of the nonlocal parameter () that are applied in the NGWB elasticity model and to validate and evaluate the obtained results. Since the NGWB elasticity model considers the size-dependent effect on the vibrational behavior, obtained results from it well agrees with the MD simulation results in the present study. For CCNTs, there was a coupling between transverse, longitudinal, and torsional vibrations, which led to the beating phenomenon. The natural frequencies decreases by increasing the number of pitches ( aspect ratio and pitch angle The nonlocal parameter has a more significant effect on the frequencies of CCNTs with smaller geometrical parameters. In addition, the type of boundary conditions affects the calibrated values of the nonlocal parameter, frequency values, and arrangement of vibrating mode shapes of CCNTs. Results of the present study can be applied in the design and analysis of nano-electro-mechanical systems (NEMS), sensors, and nano-composite structures containing CCNTs. Also, the NGWB elasticity model might be useful in the statics and wave propagation studies of CCNTs, and other coiled and curved nano-structures.

Clinical Assessment of a Novel Ring Gantry Linear Accelerator-Mounted Helical Fan-Beam kVCT System

PurposeTo assess clinically relevant image quality metrics (IQMs) of helical fan beam kilovoltage (kV) fan beam computed tomography (CT). Methods and MaterialskVCT IQMs were evaluated on an Accuray Radixact unit equipped with helical fan beam kVCT to assess the capabilities of this newly available modality. kVCT IQMs were evaluated and compared to a kVCT simulator and linear accelerator-based cone beam CTs (CBCT) using a commercial CBCT image quality phantom. kVCTs were acquired on the Accuray Radixact for all combinations of kVp and mAs in fine mode using a 440-mm field of view (FOV). Evaluated IQMs were spatial resolution, overall uniformity, subject contrast, contrast-to-noise ratio (CNR), and effective slice thickness. Imaging dose was assessed for planar kV imaging. ResultsOn this kVCT system spatial resolution and contrast were consistent across all settings with 0.28 ± 0.03 lp/mm and 9.8% ± 0.7% (both 95% confidence interval). CNR strongly depended on selected mode (views per rotation) and body size (mA per view) and ranged between 7.9 and 34.9. Overall uniformity was greater than 97% for all settings. Large FOV was not found to substantially affect the IQMs whereas small FOV affected IQMs due to its effect on pitch. Technique-matched CT simulator scans were comparable for uniformity and contrast, while spatial resolution was higher (0.43 ± 0.06 lp/mm), and CNR was between 4% (140 kVp) and 51% (100 kVp) lower. For kV-CBCT, spatial resolutions ranging from 0.37 to 0.44 lp/mm were achieved with comparable contrast, CNR, and uniformity to kVCT. All kVCT scans exhibit imaging artifacts due to helical acquisition. Clinical acquisitions of megavoltage (MV) CT, kV-CBCT, and kVCT on the same patient showed improved and comparable image quality of kVCT compared to MVCT and kV-CBCT, respectively. ConclusionsHelical fan beam kVCT allows for daily image guidance for localization and setup verification with comparable performance to existing kV-CBCT systems. Scan parameters must be selected carefully to maximize image quality for the desired tasks. Due to the large effective slice thicknesses for all parameter combinations, kVCT scans should not be used for simulation or planning of stereotactic procedures. Finally, improved image quality over MVCT has the potential to greatly improve manual and automated adaptive monitoring and planning.

Electron acceleration using twisted laser wavefronts

Using plasma mirror injection we demonstrate, both analytically and numerically, that a circularly polarized helical laser pulse can accelerate highly collimated dense bunches of electrons to several hundred MeV using currently available laser systems. The circular-polarized helical (Laguerre–Gaussian) beam has a unique field structure where the transverse fields have helix-like wave-fronts which tend to zero on-axis where, at focus, there are large on-axis longitudinal magnetic and electric fields. The acceleration of electrons by this type of laser pulse is analyzed as a function of radial mode number and it is shown that the radial mode number has a profound effect on electron acceleration close to the laser axis. Using three-dimensional particle-in-cell simulations a circular-polarized helical laser beam with power of 0.6 PW is shown to produce several dense attosecond bunches. The bunch nearest the peak of the laser envelope has an energy of 0.47 GeV with spread as narrow as 10%, a charge of 26 pC with duration of as, and a very low divergence of 20 mrad. The confinement by longitudinal magnetic fields in the near-axis region allows the longitudinal electric fields to accelerate the electrons over a long period after the initial reflection. Both the longitudinal E and B fields are shown to be essential for electron acceleration in this scheme. This opens up new paths toward attosecond electron beams, or attosecond radiation, at many laser facilities around the world.