High-power laser welding is widely used due to its ability to achieve deep penetration with a small heat-affected zone. However, this process often leads to spatter, caused by the interaction between unstable keyhole capillary behavior and metal vapor ejection, which can result in welding defects such as pits and material loss. Stabilizing the keyhole capillary is, thus, essential for spatter suppression. This study investigates the effect of keyhole capillary stabilization using a 3spot laser profile, in which a high-power central laser is combined with low-power preheating and postheating lasers positioned at the forward and back. Welding experiments were conducted using this configuration, and the results were compared with those obtained from conventional single-spot laser beams. The mechanism by which beam profile control using a 3spot laser contributes to spatter reduction is elucidated in this study.
Composite layers of Ti80 reinforced with SiCp and Ni-coated SiCp were prepared using laser melt injection (LMI). The effect of pre-Ni coating on SiCp was investigated in terms of the microstructural characteristics and mechanical properties of the resulting LMI layers. The results showed that the initially irregular SiCp, characterized by sharp edges, transformed into more rounded morphologies and exhibited numerous fine protrusions on their surfaces, with an average Ni-P coating thickness of approximately 2.875 μm after the electroless nickel plating process. Interface defects and a mixed TiC/Ti5Si3 reaction layer were observed in the LMI SiC/Ti80 layer. The pre-Ni coating on SiCp improved the wettability between the SiCp and the molten Ti80 alloy, resulting in defect-free interfaces and continuous TiC cellular reaction layers in the LMI Ni-coated SiC/Ti80 layer. This layer inhibited the continuous dissolution of SiCp into the Ti80 melt, allowing the injected SiCp to be retained to the greatest extent possible. Additionally, this SiCp pretreatment increased the surface hardness of the LMI SiC/Ti80 layer by 6.8% and reduced the wear rate per unit load and distance by 5.1%. The high interfacial bonding strength and the larger residual SiCp in the LMI Ni-coated SiC/Ti80 layer delayed the peeling of residual SiCp, leading to improved wear resistance compared to the LMI SiC/Ti80 layer. The wear behavior of the Ti80 substrate is predominantly governed by adhesive wear mechanisms, supplemented by oxidation and abrasive wear processes. Conversely, the LMI layers primarily experience abrasive wear, accompanied by simultaneous oxidation and adhesive wear phenomena.
Although femtosecond-laser micromachining of bulk metals has been extensively studied, the coupled effects of energy input, pulse accumulation, and focal position on the material-removal behavior and cross-sectional evolution of ultrathin molybdenum remain insufficiently understood. In this study, the effects of laser energy density, equivalent pulse number, and defocus on cutting-front stability, sidewall morphology, redeposition, and taper formation were systematically investigated. The laser energy density was found to define the stable ablation window and govern the development of periodic sidewall features. The equivalent pulse number controlled the progressive advance of the cutting front and was, therefore, critical to maintaining cross-sectional uniformity. Small variations in defocus near the focal plane produced only limited improvements in taper, whereas large positive defocus substantially reduced the difference in material removal between the entrance and exit surfaces, thereby enabling low-taper cutting. These results establish a direct relationship between processing conditions, sidewall evolution, and cross-sectional geometry in ultrathin Mo sheets. Under the optimized conditions, pure-Mo grids were fabricated with a maximum relative dimensional error of 3.8%, an average relative error below 2%, and a half-taper angle of 14.3°. The findings provide a mechanistic and practical basis for the precision fabrication of Mo-based electron-gun grids and other thin-metal functional microstructures.
This study presents the fabrication and characterization of short-cavity InGaAsP/InP (1330 nm) and AlGaInAs/InP (1550 nm) multisection diode lasers with two-section (gain and absorber) and three-section (two gain and one absorber) configurations. Smooth and anisotropic etching of surface and sidewall structures was achieved using CH4/H-2/Cl-2 gas mixtures in the waveguide etching process, conducted without heating. The fabrication process was analyzed by scanning electron microscopy, optical microscopy, and 3D profilometry to evaluate etching quality. Depending on the gas used, the smoothest surface structure with an average roughness (Ra) of 0.137 mu m and the most anisotropic profile of similar to 90 degrees were achieved. The performance of the fabricated lasers was assessed through light-current (L-I), current-voltage (I-V), and optical spectral analysis. The InGaAsP/InP laser (1330 nm) exhibited a threshold current of 2 mA, while the AlGaInAs/InP laser (1550 nm) demonstrated a threshold current of 5 mA. These results demonstrate the effectiveness of the proposed heating-free fabrication approach and confirm its suitability for compact multisection InP-based diode laser devices.
The titanium alloy Ti-6Al-4V faces severe oxidation resistance challenges under extremely harsh working conditions. Refractory high-entropy alloy (RHEA) coatings with the nominal composition of Al20V20Cr20Nb40-xMox (x = 10, 20, 30 at. %) were successfully synthesized on the surface of Ti-6Al-4V substrates via an innovative laser cladding technique. The dependence of the coatings' oxidation resistance on the Mo content was systematically examined. The Mo30 coating exhibits the best oxidation resistance, and its oxidation process conforms to the parabolic law. With the increase in Mo content, the surface oxide changes from scaly to dense granular. The oxidation products of Mo10/Mo20 coating are mainly TiO2 and Al2O3, which have weak protection. However, Mo30 coating generates composite oxides such as CrNbO4 and Al2TiO5, which effectively improve the antioxidant performance. Mo effectively inhibits oxygen diffusion by promoting the formation of a dense Al2O3 layer and an insulating layer. The study emphasizes the key role of complex oxides and dense oxide layers in improving the high-temperature oxidation resistance of the alloy at 800 degrees C, providing insights into the oxidation behavior of RHEA coatings under extreme conditions.
This study presents an integrated approach for monitoring and characterizing autogenous laser welding of Strenx 700 E high-strength steels, aiming to enhance weld quality and process reliability. A multisensory monitoring system was developed, incorporating a laser illumination welding camera with a computer vision algorithm based on morphological transformations to extract keyhole contours and analyze capillary wave behavior. Optical coherence tomography was employed to reconstruct internal keyhole geometry, providing valuable insights into subsurface features and melt pool dynamics. Additionally, an optical microphone exhibited a correlation between spectral magnitude and laser power in bead-on-plate welds. Metallurgical analysis, including cross-sectional examination and Vickers hardness testing, revealed complete penetration and good weldability at higher laser powers, with moderate to high hardness observed in the fusion and heat-affected zones. The findings illustrate the advantages and complementarity of advanced monitoring techniques, offering improved quality assurance and facilitating further advancements for more reliable and efficient laser welding processes in industrial applications requiring durable joints.
In this experimental work, optoelectronic feedback and optical injection are applied to twin laser diodes. The X-coupler passive optical component device is employed to introduce and mix optical injection as a feed-forward, while a photodetector is used to detect and modulate self-optoelectronic feedback. The generated chaotic signal is modified by the X-coupler, and a broadband carrier with 9.4 MHz is achieved when the case of the first laser diode (LD1) bias current is changed. In the case of the second laser diode (LD2) being controlled, the generated carrier bandwidth frequency range increased to 124 MHz. Justification for chaoticity is carried out by calculating fractal dimension in terms of correlation function. According to calibration, the Lyapunov exponent also confirmed the existence of chaos with selected dimensions and noise with others. The bias voltage level is in correspondence to the laser threshold-based light-current curve. Calibrated attractors corresponding to the resulting dynamics have slightly variable hyperspherical shapes with varied radii and filled areas with modes and trajectories. This technique, named double feeding, finds applications in optical neural networks with which input and hidden and output layers can be simulated and chaotic synchronization can be employed.
Fiber laser amplification usually uses amplifiers in a single core, such as a master oscillator power amplifier (MOPA). However, nonlinear optical effects resulting from the high peak power of short pulse fiber lasers limit their output [Chen et al., Opt. Express 17(26), 24008-24012 (2009)]. Coherent beam combining (CBC) systems can overcome this output limitation and achieve higher powers [Fan, IEEE J. Sel. Top. Quantum Electronics 11(3), 567-577 (2005); Yoshida, Jpn. J. Opt. 40(3), 122-128 (2011)]. On the other hand, with all-fiber CBC systems, it is difficult to efficiently amplify short pulses, which have short coherence lengths and whose phase and polarization can change due to external factors such as temperature changes and mechanical vibrations. Conventional CBC systems require precise control of both phase and polarization. To solve this problem, a novel CBC system that does not need phase or polarization control has been developed, and the successful amplification of femtosecond pulses has been reported [Kambayashi, IEEJ Trans. Electron. Inf. Syst. 136(1), 70-75 (2016)]. We attempted amplification using a novel passive CBC system, employing noiselike pulses (NLPs) as the seed light. NLPs contain numerous sub-picosecond and picosecond pulses within a nanosecond envelope. In the work reported in this paper, we achieved a highly efficient and stable combined output, demonstrating a combining efficiency of 98.7% and output fluctuations of less than 0.9% for 2 h.
In this work, a novel fluidic powder switch is developed, featuring an innovative design that enables near-instantaneous switching of a powder flow. Unlike conventional solutions, the fluid-based mechanism eliminates the need for mechanical switching elements in the powder conveying line, reducing system wear and enabling direct integration into a Laser Material Deposition (LMD or DED-LB/P) nozzle. The present work focuses on the evaluation and systematic assessment of the main functionality of toggling of a focused powder gas jet by analyzing switching times, delays caused by system inertia, and the stability and repeatability of the switching process. Measurements in a dedicated experimental setup show that a stable powder flow is consistently achieved within <200 ms, while powder deactivation occurs within <40 ms, highlighting the system's responsiveness and suitability for highly dynamic LMD and extreme high-speed laser material deposition processes. A high repeatability was demonstrated with rapid switching trials showing a standard deviation of as low as 1.74 and 24.1 ms between switching cycles for “time to powder on” and “time to stable powder flow,” respectively. In direct comparison with a commercially available mechanical powder switching system, the fluidic solution presented in this work demonstrated an improvement in responsiveness of approximately 83% under identical test conditions.
To advance the development of high-performance surface protective coatings, this study employed laser cladding technology to fabricate FeCoNiSi1.Cr-5(x) (x = 1, 1.2, and 1.5) high-entropy alloy coatings on 304 stainless steel substrates. The effects of different chromium concentrations on the microstructure, wear resistance, and corrosion resistance of the coatings were systematically investigated. Experimental results demonstrate that increasing the Cr content enhances the quantity of hard phases in the coating, leading to a significant improvement in microhardness. When x = 1.5, the wear volume of the coating was reduced by 80% compared to x = 1. Furthermore, in both tested corrosive media, the 304 stainless steel substrate exhibited inferior corrosion resistance to the high-entropy alloy coatings. In a 3.5 wt. % NaCl solution, an increase in the Cr content lowered the corrosion potential, reduced the impedance radius, and resulted in an overall decline in corrosion resistance. In a 0.5 mol/l H2SO4 solution, the corrosion resistance of the coating initially improved with increasing the Cr content, reaching an optimum at x = 1.2; however, further increasing the Cr content led to a deterioration in corrosion performance.
Pure copper is a difficult material to weld due to its high reflectivity to infrared (IR) lasers. Various approaches have been taken in laser welding copper to improve welding quality. In recent years, beam shaping technologies that create a ring-shaped intensity distribution for IR laser and Blue-IR hybrid laser have been developed and are being adopted in mass production lines. However, few phenomenological studies have directly compared these two technologies. In this study, we performed bead-on-plate welding of pure copper plates using an IR single spot beam, an IR ring core beam formed by a diffractive optical element, and a Blue-IR hybrid beam and compared the bead quality, the number of melt ejections and spatters, and the keyhole behavior. As a result, it was found that there was a clear difference when the welding speed was low. At a welding speed of 2.5 m/min, melt ejections occurred in the IR single spot and the IR ring core, resulting in bead defects. On the other hand, the Blue-IR hybrid did not cause melt ejections and formed a stable molten pool and bead. When observing the internal behavior of the keyhole at a glass-assisted side-view observation method, unstable fluctuations in the keyhole shape, spatter, and melt ejection were observed when the IR ring core was applied. In the Blue-IR hybrid, the keyhole and the liquid phase in front of the keyhole were formed stably, and no spatter or melt ejection was observed.
In the precision-driven domain of laser welding, achieving consistent high-quality welds while maintaining process efficiency poses a significant challenge. This paper introduces a low-latency AI-based framework designed to optimize the laser welding process in real time, addressing this challenge through advanced monitoring and control. The system comprises two key components: an AI-based monitoring system and an AI-based controller. Utilizing data from a high-speed camera and a high-speed microphone, the monitoring system integrates multiple AI models and data fusion to predict four critical quality measures. These include surface quality parameters and subsurface characteristics, such as weld depth and bonding width, with weld depth predictions achieving less than 10% error. The control system leverages these real-time assessments to compute optimal process parameters, ensuring continuous process optimization. It manages seven control parameters, including x-y beam oscillation and power modulation, with monitoring inference in approximately 2-3 ms, control computation in approximately 1 ms, and a total reaction time of approximately 10-25 ms. A stochastic digital twin simulator facilitated system testing and tuning prior to deployment. The novelty of this work lies in achieving low-latency operation under high complexity (four quality measures, seven control parameters). In surrogate-based stochastic closed-loop simulations calibrated from copper-electrode welding experiments, the proposed controller reduced the simulated quality deviation from target values by 29%-48%, depending on the quality measure.
Graphene-reinforced AlSi10Mg matrix composites are high-strength materials with significant potential for applications involving high thermal and mechanical loads. The composite has a promising future in catering to the automobile and aerospace sectors due to its exceptional properties. Considering this, the current study explores the thermal, surface, and compressive properties of 0.1% graphene-reinforced AlSi10Mg composite fabricated using the selective laser melting process. The study examines the effect of process parameters, including laser power (200-400 W), layer thickness (30 and 60 mu m), hatch spacing (50-90 mu m), and graphene reinforcement, on compressive strength, surface properties, and thermal behavior. The results indicate that the increasing volumetric energy density improves the compressive strength and wettability properties, while also increasing surface roughness. Furthermore, wettability and compressive strength improve with the higher laser power, while surface roughness and wettability are at their lowest at 70 mu m hatch spacing. The incorporation of graphene enhances the reaction temperature, thermal stability, and heat absorption, while also affecting the precipitation of the intermetallic compound of the composite.
Laser guards are critical components for ensuring safety in laser processing systems. While current safety standards and regulations establish general protection requirements, the existing correction functions for beam diameter effects have proven to be outdated. The findings of this study demonstrate that the established scaling model drastically overestimates the actual laser resistance. In this study, a standardized testing box was developed to systematically investigate the laser resistance of various plastic and mineral glass filter materials. Laser exposure tests were conducted using near-infrared and visible laser radiation across a wide range of beam diameters d86 from 1 to 100 mm. The results demonstrate that the maximum tolerable irradiance exhibits a power-law dependence on the laser beam diameter for all investigated materials. A significant finding of this work is that normalizing the irradiance to a beam diameter of 20 mm (E20), rather than the 1 mm diameter often used in standards, significantly reduces data scatter and enables a more reliable scaling. Based on these findings, a new material-independent, piecewise correction function, incorporating a plateau for small beam diameters, is proposed. This function allows the calculation of the protective exposure limit across the entire diameter range based on individual standard tests. This advancement provides a robust methodology to enhance the safety, practicality, and cost-efficiency of laser safety systems while reducing the need for extensive case-specific suitability testing.
Thermal performance of passive heat spreader vapor chambers is mainly determined by the performance of evaporation, which is highly dependent on the permeability of wicks. Most existing studies on wick permeability focus on the wick itself, while the effects of fabrication and assembly processes are often overlooked. In this paper, accurate V-shape microgrooves were fabricated by femtosecond laser efficiently with a diffractive optic element, and their capillary behavior was experimentally characterized using de-ionized water. A theoretical model was developed to describe liquid transport in such geometries, and finite-element simulations further validated the theoretical predictions. In addition, the degradation of permeability during heat treatment and prolonged air exposure was systematically investigated, and an effective recovery method was proposed. This finding provides a framework for optimizing groove fabrication and preserving wick performance during vapor chamber manufacturing.
In this work, the thermo-optic coefficient is studied in the temperature range between 100 and 800 degrees C by utilizing fiber Bragg grating technology. The thermo-optical coefficient was found to rise with temperature. Simulation is used for several related parameters. Reflected wavelengths were created by applying coefficients of thermal expansion, thermo-optical coefficients, and induced temperature ranges. The wavelength of light reflected from a specific light source spectrum is determined by the temperature-induced changes in the grating period and refractive index. The effect of sensor length is also studied by the application of specific lengths. A sensor length value of 15 mm represents the length that achieves the ideal balance (optimal balance) between high sensitivity and spectral stability. At this length, the sensitivity is 14.8 pm/degrees C, a very strong value and very close to the peak, but with greater stability in the waveform.
Real-time synchronization between physical and virtual welding is hindered by the high cost of multiphase computational fluid dynamics simulations. We propose a laser-welding digital twin (LWDT) that enables online penetration-state prediction through a Gaussian-process-parameterized Markov chain model. The LWDT integrates a physics model that supplies melt-pool and keyhole features, a data-assimilation procedure that fuses simulated keyhole areas with vision-based penetration labels, and an online-learning pipeline that continually updates transition probabilities with new process data. Initialized with 150 power-speed-thickness combinations and updated with 450 additional samples, the predictor achieves mean value error 9.48% and RMSE 9.67%, which further decrease to 4.96% and 5.14% after online learning. A 1-s sequence is generated in 0.0147 s, whereas an equivalent high-fidelity simulation requires approximate to 110 h, demonstrating orders-of-magnitude speedup while preserving prediction accuracy. The LWDT, thus, provides a practical route to process-level, real-time quality inference and control in laser welding.
Traditional nondestructive detection of hidden cracks in concrete generally suffers from low accuracy, poor anti-interference ability, high cost, and highly specialized operation. Digital shearing speckle pattern interferometry has a simple structure, high precision, strong anti-interference ability, and low cost and has been widely used in nondestructive detection. However, this technology has not been fully studied in the field of nondestructive detection of hidden cracks in concrete, so this study aims to evaluate its application potential in the detection of hidden defects in concrete. First, the mathematical model of light intensity, phase, and out-of-plane displacement derivative (strain) was established, and a digital shear speckle interference platform was designed and built. Second, loading the measured object detects the out-of-plane strain in different directions. Third, the effects of the shear amount and shear direction on imaging clarity and defect detection rate were explored through simulated concrete components and defects. Finally, the application potential of concrete hidden crack detection in an engineering environment is verified. Experimental results show that the digital shear speckle interferometry system can directly measure the strain concentration information of the object under detection. When the shear direction and shear amount are 12 -15 mm in the y-direction, the shear imaging clarity is the highest, and the success rate of defect detection reaches 80%, and the system successfully detected the hidden crack in concrete under the interference of pit and hole defects on the surface, promoting the application of this method in nondestructive detection of hidden cracks in concrete.
Glass fiber-reinforced plastic (GFRP) composites have been increasingly utilized in the aerospace industry owing to their distinctive properties such as high mechanical strength, low density, and design flexibility. However, conventional machining methods such as drilling, milling, and sawing are usually limited when machining these materials due to the caused severe tool wear, composite delamination, and thermal damage. Herein, a femtosecond laser machining method was explored to realize precision machining of sandwich-structured GFRP composites with significantly suppressed thermal damage, burr formation, and delamination. Comprehensive machining quality was evaluated on the basis of penetration depth, surface morphology, and machining efficiency through optimizing the main parameters of laser fluence, scanning speed, and laser scanning repetitions. Results showed that the smoothest cut surface with a clean edge and minimal heat-affected zone was obtained at a laser fluence of 9.21 J/cm(2). Within the experimental range, the higher scanning speed resulted in smoother cut surfaces and reduced thermal defects. The study provides experimental evidence for optimizing femtosecond laser micromachining of GFRP composites and contributes to a deeper understanding of laser-composite interaction mechanisms.
This study investigates the laser oscillating welding process applied to 2 mm-thick 5052 aluminum alloys. The ANSYS Welding software is employed to simulate and calculate the temperature field under various welding parameters, including welding speed, swing frequency, swing mode, and defocusing amount. The simulation results are subsequently validated through experimental testing. Using a high-speed camera to dynamically analyze the plasma morphology and melt pool flow behavior under different oscillating modes, establish a finite element model to simulate the welding process and analyze the influence mechanism of the combination of process parameters on the weld seam forming. The study shows that the circular oscillating suitability is excellent; when the welding speed is 10 mm/s, the heat input is suitable, and there is no weld fusion and no weld penetration; At a laser defocusing amount of -2 mm, it can guarantee the stability of the depth of fusion and avoid the heat input is too large; when the laser frequency is increased to 60-65 Hz, the molten pool stirring effect is enhanced due to the increase in the frequency, which improves the uniformity of weld bead. The optimal parameter combination is determined through process analysis, test verification, and optimization simulation results.
