Laser Profile Research Articles

Variable laser profiles and polarization states in the wave-mixing scheme for the generation of THz radiation in collisional-magnetized clustered-plasma

The four-wave mixing (FWM) mechanism for the generation of Terahertz (THz) radiation in magnetized-collisional clustered-plasma is studied. Clusters can trap the incident laser fields, leading to efficient energy transfer to plasma electrons and the creation of a strong nonlinear current. The size and density of clusters can be tuned to control the emission of THz radiation. The smaller clusters can bring about higher intensity THz radiation, while larger clusters can contribute to the broader THz frequency range. The THz radiation angular distribution patterns in the forward direction have been assessed, and the impact of plasma interaction length, cluster radius, and plasma electrons collision frequency on the generated THz wave patterns has been investigated. The FWM analysis highlights the importance of plasma clusters as well as magnetic fields in the efficient generation of THz emission. The model also takes into consideration how an induced electron current density initiated by DC external magnetic field can boost radiation power without changing the directivity diagram.

Two Contributions to Rolling Contact Fatigue Testing Considering Different Diameters of Rail and Wheel Discs

Scaled rolling contact fatigue tests, used to practically simulate the wear of the wheel and rail material under laboratory conditions, are typically classified into two categories. Tests in the first category use twin-disc stands, while the second group of test rigs use two discs of different diameters considering the rail disc as the larger one. The latter setup is closer to the real situation, but problems can occur with high contact pressures and tractions. The focus of this paper is on two main contributions. Firstly, a case study based on finite element analysis is presented, allowing the optimization of the specimen geometry for high contact pressures. Accumulated plastic deformation caused by cycling is responsible for abrupt lateral deformation, which requires the use of an appropriate cyclic plasticity model in the finite element analysis. In the second part of the study, two laser profilers are used to measure the dimensions of the specimen in real time during the rolling contact fatigue test. The proposed technique allows the changes in the specimen dimensions to be characterized during the test itself, and therefore does not require the test to be interrupted. By using real-time values of the specimen’s dimensional contours, it is possible to calculate an instantaneous value of the slip ratio or the contact path width.

New Approach for Processing Recycled Carbon Staple Fiber Yarns into Unidirectionally Reinforced Recycled Carbon Staple Fiber Tape.

This study describes a novel process in which staple fiber yarns made from recycled carbon fibers (rCFs) and polyamide 6 (PA6) fibers are further processed into semi-finished tape products in a modified impregnation and calendaring process. In this process, the staple fiber yarns are heated above the melting temperature of the polymer, impregnated, and stretched to staple fiber tapes (SF tapes) in the calendaring unit. SF tapes with different degrees of stretching and/or repasses were produced. The individual width and thickness were measured in line by a laser profile sensor. From these tapes, preforms were manually laid and processed into laminates in an autoclave. The important physical properties of the unidirectionally reinforced laminates made of the tapes were compared with organic sheets wound from staple fiber yarns. With increasing stretching, both the fiber orientation and mechanical properties improved compared to the organic sheets made from unstretched staple fiber yarns. An improvement in fiber orientation relative to the process direction from 66.3% to 91.9% (between ±10°) and 39.1% to 71.6% (between ±5°), respectively, was achieved for a two-stage stretched tape. The tensile and flexural moduli were increased by 15.2% and 14.5%, respectively.

Trajectory planning of deep-cutting laser profiling of superabrasive profile grinding wheels

The low profiling efficiency is the key barrier to the industrial application of laser dressing technology for profile grinding wheels. In this paper, the trajectory planning method of deep-cutting laser profiling was proposed for the first time, the theoretical model of the energy distribution of the Gaussian laser beam on the surface of the profile grinding wheel was established, and the effect of this method on improving the profiling efficiency of superabrasive profile grinding wheel was systematically studied. Through comparative experiments, it was confirmed that the trajectory planning method could effectively improve the profiling efficiency of the V-shaped grinding wheel, and it was found that the smaller the tip angle, the greater the efficiency improvement. The change of grain size will lead to the change of grain removal method, which will affect the profiling efficiency of V-shaped grinding wheel, but it has little influence on the profiling accuracy. The V-tip arc radius of the diamond grinding wheel with a particle size of 20–180 μm after laser profiling could be controlled between 10 and 20 μm, which was difficult to achieve by mechanical or electrical dressing method. The trajectory planning method could also significantly improve the profiling efficiency of convex/concave arc-shaped grinding wheels, and the greater the arc radius or chord-to-diameter ratio of the grinding wheel, the greater the efficiency improvement. Even though convex/concave arc-shaped grinding wheels were the same size, their profiling efficiency and material removal efficiency were quite different. For grinding wheels with different arc radii or chord-to-diameter ratios, different process strategies should be selected during laser profiling to ensure a comprehensive balance between efficiency, accuracy and quality.

Effect of different Gaussian-like laser profiles on electron energy gain in laser wakefield acceleration

Effect of different Gaussian-like laser profiles on electron energy gain in laser wakefield acceleration

Comparative analysis of laser profile cutting of Ni-based superalloy sheet using RSM and ANN

Comparative analysis of laser profile cutting of Ni-based superalloy sheet using RSM and ANN

Caracterização morfométrica da bacia hidrográfica do rio Tapacurá, Pernambuco, Brasil

The morphometric characterization of a river basin represents an important mechanism for the management of water resources, as it is directly related to its hydrological regime. These characteristics can be obtained from the processing of Digital Elevation Models (DEM) in a Geographic Information System (GIS) environment. The present study sought to analyze the morphometric characteristics of the Tapacurá river basin, a sub-basin of the Capibaribe river that is located between the Zona da Mata and Agreste mesoregions of the state of Pernambucano, using DEM from airborne laser profiling (LiDAR) . The automatic delimitation of the basin was carried out, the extraction of its hydrographic network and, consequently, the obtaining of its geometric, hydrographic and relief morphometric parameters. From the results, it was verified that the Tapacurá river basin has an elongated shape, giving it a low propensity to floods, encompasses a regular drainage system, its main channel has a rambling shape and has elevations that vary from 40.06 m to 576.30 m. m. Knowledge of these characteristics constitutes an important instrument in the management and planning of water resources in the region, and can be used as a support for decision-making by managers and/or professionals in the area, in order to support the development of public policies that provide harmonious coexistence. between the population and water resources.

Effects of Laser-Powder Alignment on Clad Dimension and Melt Pool Temperature in Directed Energy Deposition

Abstract The process parameters of Directed Energy Deposition (DED) have been widely studied including laser power, powder flow rate, and scanning speed. These parameters affect clad dimension and melt pool temperature, which are directly related to part quality. However, laser/powder profiles and their alignment have obtained less attention due to the cumbersome characterization process, although they can be directly associated with local energy density for melt pool formation. This study examines the impact of the alignment between the laser beam and powder flow distributions in DED on clad dimension and melt pool temperature. The laser beam and powder profiles are characterized by measuring their respective 2D Gaussian profiles for a given standoff distance. Aligned and misaligned laser-powder profiles are then used to build single-clad square geometries. It was found that a 500-µm offset between the centers of the laser and powder profiles causes up to a 20% change in both the width and the height of a single clad as well as an average temperature increase of 100 K. To understand the interaction between powder flow, energy flux, and local temperature, the local specific energy density distribution was plotted in 2D. These results suggest that laser-powder misalignment may significantly alter the thermal history and shape of deposited clads, possibly preventing DED-manufactured parts from meeting design properties and causing build failures.

Assessment of chemo-mechanical degradation of concrete sewer pipes through an integrated experimental approach

The chemo-mechanical degradation of unreinforced concrete sewer pipes applied in domestic service locations is assessed through a systematic, integrated experimental approach, considering 18 new and 35 used sewer pipes. The characteristics and environmental conditions of the sewer pipes are reported, and data obtained from surface condition classification, residual alkalinity tests and XRD analyses are combined to identify the type and degree of chemical attack of the used sewer pipes. Concrete material properties are determined by material tests on sewer pipe samples, providing quantitative insight into the age dependency of the Young’s modulus, compressive strength, tensile strength and mode I toughness. All relatively old pipes (installed in the 1920s and 1950s) show substantial chemical attack by biogenic sulphide corrosion (at the inner side of the pipe) and carbonation (at the outer side of the pipe). The time development of the corresponding corrosion depths on average follows a linear trend, whereby the corrosion rate for biogenic sulphide corrosion is about a factor of 1.3 larger than for carbonation. Due to these chemical processes, the mechanical properties of concrete may significantly depend on the age of the sewer pipe. In particular, the average compressive strength and average tensile strength decrease approximately linearly with the age of the pipe, in correspondence with relative reductions of, respectively, a factor of 1.7 and 1.5 over a period of almost 100 years. The values and time-dependent trends found for the concrete properties and corrosion depths of sewer pipes can serve as input for practical analyses and advanced numerical simulations on their bearing capacity and time-dependent degradation. The experimental results also emphasize the importance of regularly assessing the amount of chemical degradation of (especially older) in-situ sewer pipes, by determining the (decrease in) effective wall thickness via core sampling and laser profiling.

Proof of Concept: In-Situ Wear Differentiation of Simultaneously Wearing Counterparts

Accurate assessment of the tribological system’s wear behavior is crucial for optimization. Common tribological test stands rely on a single measurement information—usually the indentation depth of the complete tribological system. If both counterparts experience wear—like polymer–polymer combinations—a subsequent assessment of the tested specimens is needed to estimate the contributions of each partner for determining the wear volume, and thus the wear rate. In this work, we propose a novel approach how an in-situ wear measurement of both simultaneously wearing counterparts can be implemented and generally demonstrate the feasibility on a ball-on-prism tribometer. This is achieved by measuring the system’s indentation depth while simultaneously scanning the ball’s surface with a laser profile scanner, providing information for calculation of the ball’s wear volume. While offering new possibilities for wear evaluation, challenges remain including radial runout of the measured specimen, testing in media and accumulation of large amounts of debris. Overall, this work presents an advancement in the evaluation of wear behavior, enabling better optimization of tribological systems with simultaneous wear. Refinements and adaptations to different setups can further enhance its utility.

Study of particle acceleration by Laguerre–Gaussian ultra intense laser plasma interactions

In this work, simulations of multi-petawatt lasers in the range of ∼0.2 PW–∼100 PW with varying Laguerre–Gaussian (LG) azimuthal modes as well as linearly polarized (LP) and circularly polarized (CP) laser beams striking near critical density targets were studied by using three-dimensional particle in cell (PIC) codes. Particle acceleration mechanisms have a dependence on laser polarization and it affects the energy gained by the particles. It is known that laser pulses can be polarized helically by applying the LG distribution function to the fundamental Gaussian laser profile. In this study, differently polarized laser beams with varying powers were employed to study laser driven particle acceleration and compares accelerated charged particles’ energy spectra and angular distribution. It is seen that LG laser beams can accelerate higher energetic particles due to higher conversion efficiency compared to LP and CP laser beams. It is also seen that LG laser beams can collimate ions with a narrower spread compared to LP and CP beams. Furthermore, ions can have a smaller divergence angle with increasing azimuthal mode index when the laser is LG polarized. We also studied the energy deposition of these particles in a water cell obtained by the PIC codes for different laser parameters by using Geant4 Monte Carlo simulations which suggests that LG laser beam can be useful for the future hadron therapy applications.

Influence of rippled density and laser profile on third harmonic generation using cosh‐Gaussian laser pulses in inhomogeneous magnetized plasmas

AbstractThe third harmonic generation of cosh‐Gaussian laser pulses in inhomogeneous magnetized plasmas is investigated. The plasma is considered inhomogeneous with a sinusoidal form, and the external magnetic field has an oscillating wiggler structure. Various ponderomotive forces are obtained considering the external magnetic field, the magnetic field of the laser beam, and different orders of electron velocity. These forces are nonlinear, which leads to a nonlinear current density. Using linear and nonlinear current densities and Maxwell's equations, the wave equation of the third harmonic wave is obtained. Results show that by increasing the deviation parameter from the center and the external magnetic field, the third harmonic electric field increases. It is also indicated that by increasing the laser beam width, the excited electric field decreases. Finally, it is found that by increasing the wavenumber and amplitude of the rippled electron density, the amplitude of the third harmonic electric field increases.

Validation Technique for Heavy Vehicle Simulator Rut Measurement with Florida Laser Rut Meter

Abstract The performance of a pavement system is typically measured in structural and functional terms. Agencies often prioritize minimizing rutting as it indicates the mixture and structural inadequacy and can lead to safety concerns such as hydroplaning. Therefore, accurate rut depth measurement is critical to pavement management as well as to assess the performance of materials designed to resist rutting. To that measure, Florida Department of Transportation (FDOT) uses two heavy vehicle simulators (HVSs) as part of an accelerated pavement testing (APT) program to advance pavement research and implement new pavement materials, designs, and construction methods. Each HVS device is equipped with an on-board laser profiling system for rut depth measurement. To ensure accurate and reproducible rut depth measurements, a laser-based reference device was developed and constructed by FDOT to verify rut depth measurements made by both HVS devices during APT research studies. This article describes the rut depth reference device, the verification process, and data analysis methods used to validate the accuracy of the HVS devices.

Experimental and numerical investigations on the effect of a novel internal surface micro-grooving toward improving convective heat transfer performance of tube heat exchangers

In the present work, the use of passive heat transfer enhancement technique through surface alteration was explored. The enhancement was achieved through internal conduit surface micro-grooving using a new apparatus that was developed by modifying a magnetic abrasive finishing technique. A new surface profile was created and later verified using optical and laser profiler measurements. The new profile was numerically investigated to compare the heat transfer and hydrodynamic performance against other profiles that have been studied in the literature. It was found from the results that the new profile shows much higher heat transfer improvement and comparable pressure loss to the previously investigated profiles (i.e., square, rectangular, trapezoidal, and circular). Overall, the new groove geometry provides the highest performance followed by the circular, triangular, curvy, square, and rectangular grooves. Also, the results indicate that designs with a smooth profile performs better than those with sharp edges, owing to the elimination of stationary fluid spots within the grooves. The effectiveness between the profiles was compared based on the level of heat transfer enhancement against the flow penalty. Experimental validation was further conducted for the experimentally generated groove. The results revealed that a relatively small surface temperature drop was obtained, corresponding to a slight improvement in heat transfer. This confirms the results generated by the simulation that groove size plays a major role in attaining significant improvement in heat transfer.

Measurement and Analysis of the Influence Factors of Tractor Tire Contact Area Based on a Multiple Linear Regression Equation

Tractor tire three-dimensional (3D) contact area is one of the significant concerns of the soil-tire coupling mechanism, and it influence soil compaction and the sustainable development of agriculture. In this study, we developed a method to measure the 3D contact area of a pneumatic tire using a laser profiler on a signal tire soil-bin testing facility. A 6.00-14 bias-ply tire with high lugs was driven on sandy loam soil in a soil-bin testing facility under different vertical loads, driving speeds, and inflation pressures. Then, we developed a multiple linear regression equation between the influence factors and tractor tire contact area. The results indicated that the contact area was impacted by the three factors involved in this study, and the inflation pressure significantly influenced results, and the combination of high speed (3 m/s), low inflation pressure (69 kPa), and high tire load (2.5 kN) led to a relatively high contact area on the soil-tire contact interface and possible severe soil compaction. Also, we found that the contact area varied in a quadratic manner with speed at a given inflation pressure and tire load and varied in a quadratic manner with inflation pressure at a given speed and tire load and varied linearly with the tire load for a given speed and inflation pressure.

Betatron Radiation and Bremsstrahlung in the Interaction of Intense Laser Pulse with Solid Target

X-ray generation via synchrotron radiation and bremsstrahlung in the interaction of short laser pulses with a solid target is of much current interest owing to its numerous applications. The efficiency of laser to X-ray energy conversion is thus a crucial factor. We found that the energy conversion efficiency of synchrotron radiation and bremsstrahlung is mainly governed by the ratio of the laser pulse width to the preplasma width, which is in turn governed by the laser profile, intensity, and spot size. Synchrotron radiation dominates when the ratio is less than unity, otherwise bremsstrahlung dominates. The type of radiation can thus be controlled by tailoring the laser parameters.

Modeling of the driver transverse profile for laser wakefield electron acceleration at APOLLON research facility

The quality of electron bunches accelerated by laser wakefields is highly dependant on the temporal and spatial features of the laser driver. Analysis of experiments performed at APOLLON PW-class laser facility shows that spatial instabilities of the focal spot, such as shot-to-shot pointing fluctuations or asymmetry of the transverse fluence, lead to charge and energy degradation of the accelerated electron bunch. It is shown that PIC simulations can reproduce experimental results with a significantly higher accuracy when the measured laser asymmetries are included in the simulated laser's transverse profile, compared to simulations with ideal, symmetric laser profile. A method based on a modified Gerchberg–Saxton iterative algorithm is used to retrieve the laser electric field from fluence measurements in vacuum in the focal volume, and accurately reproduce experimental results using PIC simulations, leading to simulated electron spectra in close agreement with experimental results, for the accelerated charge, energy distribution, and pointing of the electron beam at the exit of the plasma.

Real-time measurement of minimum cross-sectional area and radius of curvature of miniature plate specimens using a high-speed laser profiler for calculating true stress-true strain curves

True stress-true strain curves are fundamental for designing and analyzing structures such as fusion reactors. These curves are typically obtained by conducting tensile tests on round bar specimens. However, due to material dimension limitations, plate specimens are sometimes used instead of round bar specimens. Obtaining true stress-true strain curves experimentally from plate specimens can be challenging. To address this challenge, this study aims to obtain true stress-true strain curves of miniature plate specimens using both analytical and experimental methods. The analytical method involved inverse finite element method (FEM), while the experimental method utilized real-time measurement of the minimum cross-sectional area and radius of curvature of a miniature plate specimen with a high-speed laser profiler. Comparing the true stresses obtained from the analytical and experimental methods, we found that the difference was typically within 5%. These findings suggest that inverse FEM and laser profilometry are effective methods for determining the true stress-true strain of miniature plate specimens.

Effect of scan strategy on the formation of a pure nickel single-crystal structure using a flat-top laser beam via laser powder bed fusion

ABSTRACT In this study, the role of a scan strategy in the fabrication of a single crystal (SX) structure of face-centered cubic (fcc) pure Ni using a flat-top laser profile by a laser powder bed fusion (LPBF) process was investigated. A flat-top laser with a uniform heat intensity across the beam profile was employed to fabricate the SX structure with a <001> texture parallel to the build direction (║BD). A meander scan strategy with an XY–90° scan rotation was required to achieve the flat-top-derived SX structure. The meander scanning strategy promoted the epitaxial <001> fcc growth along the direction ║BD, leading to the <001>║BD texture formation. Meanwhile, the XY–90° scan rotation induced the epitaxial growth of <001> fcc phase on the hatch direction (HD)–scan direction (SD) plane in the direction deviated by approximately 45° relative to the SD. This 45° deviation relative to the SD occurred to accommodate the beam movement and the circular beam geometry on the HD – SD plane, resulting in the preferred configurations of <011>║SD and HD. Thus, this paper reports the importance of meander scanning with a 90° scan-rotation strategy to yield a flat-top-LPBF-derived SX structure with <001>║BD and <011>║SD and HD textures.

Full-Scale Evaluation of Geosynthetic-Reinforced Hot Mix Asphalt

This study aims to evaluate the potential of using geosynthetics to reinforce flexible pavements and improve their resistance to reflective cracking. To achieve the goals, three full-scale test strips (control, geogrid, and geotextile) were constructed at Rowan University, each being 30 ft long by 15 ft wide. The pavement structure of each test strip included two hot mix asphalt (HMA) layers with a total thickness of 3.0 in., and five intentional cracks (with widths of 0.2 in.) were introduced to the first HMA layer. After sealing the cracks and applying the tack coat layer, the geosynthetic interlayer was added, and the top HMA layer was constructed. Asphalt strain gauges and thermocouples were embedded in each section to measure critical strains. All sections were also loaded using a heavy vehicle simulator (HVS) with dual-tire configurations while the temperature around the test strips was maintained at 50°F. In addition, each test strip’s deflection and rutting were measured before and after HVS loading using a heavy weight deflectometer and a laser profiler, respectively. The HVS loading results found that the geogrid-reinforced test strip had a better strain response than the geotextile-reinforced layer, and the geotextile-reinforced layer showed slightly higher bonding (lower delamination). It is noted that the results of this study are in line with a former laboratory study with respect to crack reflection and delamination. Rut profiler data recorded a 25% reduction in rut depth for reinforced sections compared to the control. Moreover, the geosynthetic interlayer was able to mitigate reflective cracking propagation. Both interlayers improved fatigue performance.