Laser Beam Spot Research Articles

NEUROBIOLOGICAL PROPERTIES OF THE STRUCTURE OF THE PARALLEL-HIERARCHICAL NETWORK AND ITS USAGE FOR PATTERN RECOGNITION

The paper presents the analysis of neurobiological data on the existence of the structure of a parallel-hierarchical network. Discussed method of parallel-hierarchical transformation based on population coding and its application for the pattern recognition task. Based on the analysis, we can conclude that using the methods proposed, it is possible to measure the geometric parameters and properties of images, which can significantly increase the efficiency of processing, in particular estimating the center of mass based on moment characteristics. Experimental results demonstrate that due to various destabilizing factors, accurately measuring the energy center coordinates of laser beam spot images is challenging. However, training the PI network and classifying the fragments into "good" and "bad" can considerably enhance the accuracy of these measurements.

REVIEW OF SILVER NANOPARTICLE SYNTHESIS USING LASER ABLATION; ITS CHARACTERIZATION, ANTIOXIDANT AND ANTIBACTERIAL FOR SKIN WOUNDS

This comprehensive review paper thoroughly investigates the synthesis of silver nanoparticles (AgNPs) through laser ablation and biosynthesis methods, exploring their potential applications in nanotechnology. The paper highlights the distinctive properties of AgNPs, including their notable antibacterial and anticancer attributes, wound healing capabilities, and therapeutic potential. The focus is specifically on the synthesis of small, spherical particles ranging from 2 to 5 nm. This investigation centers on key parameters crucial to the synthesis process, such as laser beam spot size, strength, ablation duration, and green synthesis factors like time, temperature, and concentration. In the realm of laser ablation optimization, the study scrutinizes the impact of various spot sizes on particle size distribution, variations in laser strength, and the intricate relationship between ablation duration and particle size. These analyses are strategically aligned to achieve the desired properties for the efficient production of AgNPs. Simultaneously, green synthesis techniques are employed to ensure an environmentally friendly approach, with careful consideration for factors like time, temperature, and concentration to attain targeted characteristics. The paper employs sophisticated characterization techniques, including dynamic light scattering (DLS), scanning electron microscopy (SEM), and UV-Vis spectral analysis, for a comprehensive analysis of the synthesized AgNPs. DLS offers insights into size distribution and stability, SEM facilitates morphology visualization, and UV-Vis spectral analysis definitively confirms the presence of silver nanoparticles through characteristic absorption peaks.

Characteristics of laser induced plasma near a flat gas-liquid interface and its effect on the performance of laser induced breakdown spectroscopy (LIBS) detection

Moving the laser focus to the vicinity of the gas-liquid interface is the key point for many new enhanced and new methods to improve the quality of spectral signals in water Laser induced breakdown spectroscopy (LIBS) detection. Understanding the generation and evolution characteristics of the plasma induced by pulsed laser near the gas–liquid interface is of great significance for the establishment of evolution models and improvement of these new LIBS methods. In this paper, a set of slow horizontal flow auxiliary system is established to provide an ideal flat gas–liquid two-phase interface experimental condition. Experimental research on vertical incidence flat system was conducted using techniques such as time-resolved imaging, plasma characterization diagnosis, and spectral analysis. And the detection capabilities of the system were also tested. The characteristics and mechanisms of LIBS near the gas-liquid two-phase interface were investigated with the laser incident on the sample along the vertical direction. Simulation of the laser beam focusing process and observation of laser beam spot images show that the shift of plasma generation position relative to the focal point results from the refraction of the laser beam entering the solution from the air and the ‘interface effect’ of propagation on the vertical direction. Moreover, the plasma forms only the optical power density surpasses the breakdown threshold. In this work, plasma with smaller size, rounder shape, stronger radiation, higher temperature, and higher density can be produced when the focus position is in the liquid column 0.3 mm away from the upper interface. Simultaneously, for example, the Mg ion line at 285.213 nm, the obtained spectral intensity to signal-to-background ratio reaches the maximum value, and a better spectral signal can be obtained, which is 2–4 times of other positions, and the detection limits of the elements Na, Mg, and Ca also reach the lowest level, with 1.6–2.4 times of the detection limit of other focusing positions for Mg and 1.4–1.7 times for Ca, respectively.

Efficient Ablation, further GHz Burst Polishing, and Surface Texturing by Ultrafast Laser

A large variety of ultrafast laser‐matter interaction regimes and different processed surface finishing qualities of stainless steel can be achieved by varying the laser processing parameters. The optimization of the laser fluence to the most efficient ablation also leads to the lowest surface roughness of the ablated material. High laser fluence together with a high pulse repetition rate leads to heat accumulation, which results in the formation of microstructures with various morphology and scales. The use of GHz bursts allows a rough stainless‐steel surface to be smoothed and even polished. In this work, the fast and high‐quality milling of 2.5D cavities is demonstrated. Laser beam spot optimization is used to increase the throughput of the high‐power femtosecond laser (67.8 W), resulting in an ablation rate of 13 mm3 min−1. The complex cavities are produced by laser milling and cutting in layers. The formation of surface structures on stainless steel because of laser irradiation has been demonstrated. The possibilities of further GHz burst polishing are examined on previously laser‐milled stainless steel using with lowest possible surface roughness. The ability to polish the surface with microstructures below the original roughness is demonstrated by bursts of ultrashort pulses with a repetition rate in the GHz range. It has been demonstrated that mold milling in stainless steel designed for LED diffusers can be fabricated using a modern femtosecond laser source together with beam size optimization technique for efficient ablation with low surface roughness, layer‐by‐layer milling techniques, and GHz burst polishing techniques.

A comparative study on resistance spot and laser beam spot welding of ultra-high strength steel for automotive applications

In this study, the effect of resistance spot welding (RSW) and laser beam spot welding (LBSW) processes on evolution of microstructure, load endurance capabilities, heat affected zone (HAZ) softening, and corrosion resistance of ultra-high-strength (UHSS) steel joints welded in lap joint design is investigated. The UHSS sheets of dual phase 1000 grade (UHSDP1000) having 1.20 mm thickness were joined using the RSW and LBSW parameters optimized by response surface methodology (RSM). The microstructural features of welding regions of RSW and LBSW joints were studied using optical microscopy (OM). The load endurance capabilities of RSW and LBSW joints were assessed using the tensile shear failure load (TSFL) and cross-tensile failure load (CTFL) tests. The ruptured surfaces of TSFL and CTFL tested samples were examined utilizing scanning electron microscopy (SEM). The microhardness distribution of divergent regions of RSW and LBSW joints was evaluated and imputed to the TSFL and CTFL failure of joints. The corrosion resistance of RSW and LBSW joints was analyzed using potentiodynamic corrosion and immersion corrosion tests. The RSW joints showed 183% and 62.79% greater TSFL and CTFL endurance capabilities than LBSW joints. The TSFL and CTFL endurance capabilities of LBSW joints are inferior to RSW joints due to the smaller load bearing area. It causes the stress concentration in FZ and HAZ of LBSW joints. The RSW joints and LBSW joints disclosed TSFL and CTFL failure in button pull out rupture mode with tearing of HAZ. The failure of RSW and LBSW joints in HAZ is due to the softening caused by martensitic tempering and coarsening of grains. The LBSW joints disclosed inferior resistance to corrosion than RSW joints due to the higher martensite content which contributes to greater fraction of favorable pitting sites and decreased corrosion resistance.

PULSED VACUUM-ARC PLASMA SOURCE WITH LASER ARC EXCITATION

A method of solution to the issue of contamination of the laser beam input window in pulsed vacuum-arc plasma sources with vacuum arc laser excitation is proposed. The method involves the periodic introduction of energy through an unfocused laser beam into a layer of condensate formed on the surface of the laser beam input window. The focus of such a cleansing laser beam is located outside the vacuum chamber, ensuring the absence of unauthorized activation of the plasma source, and the optical axis is perpendicular to the input window surface, providing optimal conditions for removing the formed condensate film. The periodicity of cleansing the laser beam input window, which determines the window throughput, is based on the condition of ensuring the probability of vacuum arc excitation not below a specified level. The area of the cleansing laser beam unfocusing spot Sunf on the laser beam input window surface facing the plasma source cathode is determined under the condition of ensuring the power density q of the laser radiation on the cleansed surface in the range of 104 ≤ q ≤ 105 W/cm2 and the condition Sunf ≥ Sexc, where Sexc is the area of the laser beam spot that excites the vacuum arc discharge on the input window surface facing the plasma source cathode. The vacuum arc excitation in the pulsed plasma source using the proposed method, which allows removing the condensate layer on the laser beam input window, is characterized by a stable 95% probability of exciting the vacuum arc at a pulse repetition frequency of 300 Hz, regardless of the plasma source operating duration.

Software compensation to improve the Stereolithography fabrication of porous features and porous surface texturing at micro-scale

Nano and micro-porous structures exhibit intriguing properties for a wide variety of applications, spanning from the biomedical to sensing. However, their fabrication is a challenge in terms of dimensional accuracy, which affects devices' performance and sensitivity. In this paper, we present a route to enhance the dimensional accuracy of fabrication via Stereolithography (SLA) of porous features at the micro-scale. Using a custom benchmark part, deviations in feature dimensions (micro-pores diameters and depths) were measured by confocal microscopy. Sample characterization and experimental observations allowed the identification of inaccuracy sources (i.e., laser spot size and its compensation on path generation), and a compensation method of the nominal laser spot diameter (85|um) was defined. Implementing such a method results in relevant improvements in dimensional accuracy: 9.8% and 11.3% on full-open pores diameter and depth, respectively. Partially open pores accuracy improvements were 15.8% on diameters and 1.5% on depths. Since machine optical equipment can result in deviations in the actual laser spot diameter from the nominal value, the actual laser beam spot diameter was estimated by printing a test part and adopting this information to adjust a calibration procedure. The measurements revealed that the actual laser beam spot size is 93±8um. The proposed method can be extended for the fabrication of any micro-porous structures.

Self-Focusing and Self-Phase Modulation of a Focused Femtosecond Laser Beam in Fused Silica at Near-Critical Peak Power

Self-focusing and self-phase modulation of focused femtosecond laser pulse were studied in bulk fused silica. Depending on pulse energy magnitude, three different regimes were observed in the experiment: (1) linear regime, when the self-focusing effect is insignificant, characterized by linear spectral broadening; (2) transition regime, when the self-focusing effect notably reduces a laser beam spot in a focal plane without considerable nonlinear absorption and beam collapse, characterized by quick increase in spectral broadening due to self-phase modulation; (3) nonlinear regime, filamentation, characterized by near-to- linear spectral broadening due to self-phase modulation. The slope for the linear and nonlinear regimes was the same within the measurement error bars. The numerical simulation, using the ray transfer matrix method, envisioned the self-phase modulation spectral broadening effect in all these regimes.

Improving Plasticity of Ferritic Stainless Steel Welded Joints via Laser Spot Control.

The plasticity of welded 441 ferritic stainless steel joints was controlled by varying the laser beam spot diameter during laser welding. A stainless steel plate thickness of 1.2 mm was used. The microstructures of the welded joints were analyzed for various spot diameters. The elongation of breaks and the reduced area of tensile specimens were analyzed to study the effects of spot diameter on plasticity of the welded joints. The results showed that the weld melt width and weld column crystal size increased with the spot diameter, but isometric crystals in the center of the weld were gradually reduced. Increasing spot diameter resulted in decreased tensile strength, elongation after breaks, and area reduction. So the parameter must be controlled during the laser welding.

Unravelling keyhole instabilities and laser absorption dynamics during laser irradiation of Ti6Al4V: A high-fidelity thermo-fluidic study

A 3D multi-phase thermo-fluidic solver is implemented to investigate the laser-melt pool interaction dynamics and keyhole instabilities during stationary and moving laser irradiation. The physical phenomena such as phase changes, thermocapillary driven flow, multiple reflections of the Gaussian laser beam and beam trapping, vaporization recoil pressure, and heat losses (convective, radiative, and evaporative) have been incorporated in the model. A detailed parametric study has been carried out to investigate the influence of the laser beam spot diameter and the traversal speed on the laser absorption dynamics and melt pool characteristics. For both the stationary and moving laser irradiation, it is found that during the initial transient stage, the melt pool morphology belongs to the conduction melting mode with laser absorption according to the normal incidence condition of the Fresnel equation. Later, depending on the irradiating laser intensity, a melt transition occurs from conduction to the keyhole mode of melting, during which laser absorption rises sharply. The laser absorption and the vapor depression morphology in the keyhole regime show substantial oscillations (periodic and non-periodic) due to the complex hydrodynamics of the recoil pressure, the surface-tension dynamics, and convection-driven flow resulting in the opening and closing of the vapor depression. These oscillations are quantified, and a direct correlation of the laser absorptance with the keyhole depression depth has been observed for stationary laser irradiation. The keyhole closure mechanism and bubble trapping-ejection phenomena have been explored during the solidification stage. The numerically predicted melt pool dimensions match well with the in-house performed experimental measurements and published benchmarking experiments combining integrating sphere radiometry and in-situ X-ray radiography.

Development of adaptive laser head for compensating error of beam waist position during processing materials using laser beam spot detection method

Development of adaptive laser head for compensating error of beam waist position during processing materials using laser beam spot detection method

A Reliable Method for Determining the Degree of Orientation of Fibrous Foods Using Laser Transmission and Computer Vision.

The degree of organised alignment of fibre structures, referred to as the degree of orientation, significantly influences the textural properties and consumer acceptance of fibrous foods. To develop a new method to quantitatively characterise the fibre structure of such foods, a laser transmission imaging system is constructed to capture the laser beam spot on a sample, and the resulting image undergoes a series of image processing steps that use computer vision to translate the light and dark variations of the original images into distinct ellipses. The results show that the degree of orientation can be reasonably calculated from the ellipse obtained by fitting the outermost isopixel points. To validate the reliability of the newly developed method, we determine the degree of orientation of typical fibrous foods (extruded beef jerky, pork jerky, chicken jerky, and duck jerky). The ranking of the measured orientation agrees with the results of pseudocolour maps and micrographs, confirming the ability of the method to distinguish different fibrous foods. Furthermore, the relatively small coefficients of variation and the strong positive correlation between the degree of organisation and the degree of orientation confirm the reliability of this newly developed method.

The effect of the diode laser beam power on the behaviour of the ZrC powder pre-coat and the 145Cr6 steel substrate during laser processing

The paper presents both the production method and its impact on selected properties of composite coatings reinforced with hard ZrC particles. The Fe/ZrC coatings were produced using diode laser by remelting the pre-coat in the form of paste consisting of ZrC powder and binder. Different values of laser beam power (500 W, 700 W, and 900 W) and different pre-coat thicknesses (100 µm, 150 µm, and 200 µm) were used to produce the composite coatings. During all processes, the scanning speed of laser beam was 3 m/min. Laser beam spot diameter was 1 mm. Microstructure study, microhardness tests, as well as EDS and XRD analysis were carried out. The obtained Fe/ZrC coatings were also tested for the effect of the corrosive medium in a 3.5% NaCl water solution. The effect of applied parameters on wear resistance of Fe/ZrC coatings was also studied. The tribological properties were assessed both by mass loss measurement and by scanning electron microscopy. Fe/ZrC coatings produced using the highest thickness of the pre-coat were characterised by cracks arising during production process. The very high concentration of carbides and hence high hardness of the coating produced in this way contributed to it. However, a positive effect of laser beam power increase on reduction of these cracks was observed. The coatings were characterised by very high hardness, reaching in some cases even more than 2000 HV. It was found that the most favourable properties regarding both tribology and corrosion resistance were obtained for Fe/ZrC coatings produced using 150 µm of pre-coat thickness.

Ultrasonic spot-welding of AA 6061-T6 aluminium alloy: Optimization of process parameters, microstructural characteristics and mechanical properties of spot joints

The ultrasonic spot welding (USW) is used to develop the lap joints of AA 6061-T6 aluminium alloy because it is difficult to spot weld using resistance spot welding (RSW) and laser beam spot welding (LBSW) processes due to its high electrical conductivity, thermal conductivity and light reflectivity respectively. The main objective of this investigation is to optimize the USW parameters specifically welding time (s), amplitude (%) and pressure (bar) for enhancing the tensile shear fracture load (TSFL) bearing capability of AA 6061-T6 aluminium alloy lap joints for automotive applications. The statistical response surface methodology (RSM) was utilized for generating strength prediction models (SPM) and validated using analysis of variance (ANOVA). The RSM is widely used for optimizing the process parameters as it provides greater information such as optimum conditions, direct effect of process parameters and performance prediction from limited number of experiments compared to other optimization techniques. The response surfaces were created using RSM and analyzed. The effect of USW parameters on macrostructure, microstructure and TSFL of USW joints was studied. From the results, it was observed that the USW joints created using the welding amplitude of 100%, welding time of 21 s and welding pressure of 6 bar exhibited greater TSFL capacity of 5.08 kN. The SPM accurately predicted the TSFL of USW joints within 5% error on 95% confidence. Welding pressure disclosed major effect on TSFL of USW joints followed by welding amplitude and time. The greater TSFL of USW joints is imputed to the better coalescence of weld surfaces and refined microstructure.

Optimization of laser beam spot welding (LBSW) parameters to maximize the load bearing capability of AHS-DP1000 steel lap joints

Optimization of laser beam spot welding (LBSW) parameters to maximize the load bearing capability of AHS-DP1000 steel lap joints

Improvements of PV receiver in laser wireless power transmission by non-imaging optics

Laser Wireless Power Transmission (LWPT) systems have an extensive prospect in the field of wireless energy transmissions such as the space control on-orbit, spacecraft sensor networks, satellites to satellite communication and power transmission, ground to ground, ground to air, ground to Unmanned Aerial Vehicle (UAV), etc. Previously, Concentrated Photovoltaics(CPV) has been used in solar energy as a solution to lower the size of the photovoltaics and yet increase efficiency. As is known laser beam spot normally presents a Gaussian distribution and laser somehow must match the size of the PV cell or array, that is how lens and concentrators are important to reshape and guide the laser beam towards the photovoltaics and in case of misalignment. The current research aims at improve the output performance of LWPT receiver by typical non-imaging optical device-Cross Compound Parabolic Concentrator (CCPC), which helps to improve the transmission of laser beam from different incident directions. Multi-field characteristics of the CPV module under laser power would be solved based on parameters from non-linear regression and experimental study. The multi-field performances of CPV module and single solar cell as the LWPT receivers have been compared. We have found that transmission distance d, divergence half-angle β, rotation angle θ and misalignment distance dmis are most important parameters for multi-field performances and LWPT conversion. The current research provides important references for LWPT system design and optimizations.

Nano-squares and regular LIPSS on YSZ coating by picosecond UV laser beam: Thin film mediated and direct texturing

The laser texturing of high bandgap ceramic materials, such as Yttrium Stabilized Zirconia (YSZ), is very challenging due to their structural complexity, their mechanical fragility as well as the risk of a chemical decomposition under laser irradiation. The objective of this paper is to fabricate, in a controlled manner, well-organized nanostructures on microscale undulating YSZ coatings, and thus evaluate the feasibility to form laser-induced periodic surface structures (LIPSS), via two experimental approaches: the first one consists in laser structuring of YSZ through a mediated thin film (gadolinium doped ceria ∼ 700 nm or Au ∼ 20 nm), while the second one involves the direct structuring of the YSZ surface under static and scanning modes. A picosecond Nd: YAG laser (355 nm, 40 ps, 10 Hz) with a relatively large laser beam spot (∼550 μm) was used. In the GDC and Au mediated texturing of YSZ under static conditions, we have observed nano-squares (∼250 nm) and typical LIPSS perpendicular to the laser beam polarization, respectively. In the case of laser irradiation of the bare YSZ surface for fluences higher than 310 ± 10 mJ/cm2, LSFL and HSFL structures were formed depending on the number of pulses (from 102 to 103). The average spatial period measured for the thus-obtained HSFL is about 136 nm with an amplitude of 40 nm, as determined by Scanning Electron Microscopy (SEM) and Atomic Force Microscope (AFM). We have also demonstrated the ability to reproduce LIPSS on YSZ under scanning mode. A “darkening” phenomenon was observed on the YSZ surface at laser fluences exceeding 600 mJ/cm2, resulting from the formation of micro-spikes (with sizes close to 1 µm). XRD measurements demonstrated a slightly lower crystallinity of the laser irradiated YSZ material compared to the untreated YSZ surface.

Open flow cytometer with the combination of 3D hydrodynamic single cell focusing and confocal laser-induced fluorescence detection

Flow cytometry is among the most powerful tools for single-cell analysis, while the high cost and mechanical complexity of the commercial instrumentation limit the applications in personalized single-cell analysis. For this issue, we hereby construct an open and low-cost flow cytometer. It is highly compact to integrate the functions of (1) single cell aligning by a lab-made modularized 3D hydrodynamic focusing device, and (2) fluorescence detection of the single cells by a confocal laser-induced fluorescence (LIF) detector. The ceiling cost of the entire hardware for the LIF detection unit and 3D focusing device is $ 3200 and $ 400 respectively. A sheath flow velocity of 150 μL/min produces a focused sample stream of 17.6 μm × 14.6 μm at sample flow of 2 μL/min, based on the LIF response frequency and the laser beam spot diameter. The assay performance of the flow cytometer was evaluated by characterizing fluorescent microparticles and acridine orange (AO) stained HepG2 cells, producing throughputs of 40.5/s and 6.2/s respectively. Favorable assay precision and accuracy were demonstrated by the agreement of frequency histogram with imaging analysis, and good Gaussian-like distributions of fluorescent microparticles and AO-stained HepG2 cells. Practically, the flow cytometer was successfully applied for the evaluation of ROS generation in single HepG2 cells.

An Efficient Method for Three-Dimensional Precise Measurement Using Laser Spot Traversal and Target Point Interpolation

Discrete point interpolation has emerged as a prime candidate technology for dual-station accurate intersection in 3-D precise measurement. However, the operation is low-efficiency for capturing multiple reference points to measure a single target point. The quantitative model of linear small angle in the interpolation is proposed by analyzing the movement trajectories of laser beam and laser spot. An efficient method for 3-D precise measurement using laser spot traversal and target point interpolation is proposed to achieve accurate intersection without multiple approximations. The laser spot traverses the field of view of the camera to establish an interpolation grid. The target point inserts the traversal grid and can be aimed by laser beam in arbitrary position. The traversal step size is determined by the determining equation of linear small angle. The approach is time-efficient for capturing all measured points in the field of view. The experimental results show that the proposed method is suitable for multiple points and surface measurement.

Generation of high intensity speckles in overlapping laser beams

A new mechanism for the generation of high intensity speckles by coupling of overlapping beams is discovered and studied in detail. Using three-dimensional simulations, the coupling of overlapping beams smoothed by phase plates and by polarization smoothing are investigated in the regime relevant to inertial confinement fusion studies. It is found that the intensity distribution of the laser beam spot can be changed by nonuniform spatial phase modulation, and the speckles formed by the phase plate can be split into smaller speckles with higher intensities, which is favorable for the generation of laser plasma instabilities. Stimulated Brillouin scattering is compared in simulations with and without coupling of the overlapping incident beams, and the results confirm the enhancement of stimulated Brillouin scattering due to this mechanism.