Laser Power Research Articles

Experimental study and neural network model based prediction of layer thickness influence on LPBF IN625 single track geometry

The performance of interacting metal surfaces having sliding motion is enhanced by fabricating microfeatures on-top of the surfaces. Laser powder bed fusion (LPBF) is used to fabricate the microfeatures of IN625 on-top of a flat surface. In LPBF, geometrical characteristics of microfeatures are based on the energy supplied and the volume of material melted (layer thickness) at that instant of time. There is very few research reported in open literature on the effect of layer thickness on microfeatures geometry during LPBF. In this work, a series of single tracks is fabricated with different combinations of laser power and scanning speed for 75 μm, 100 μm, and 125 μm layer thickness and its effect on single track geometrical characteristics and microstructure was evaluated. It has been found that laser power and scanning speed have a significant influence on the track geometry irrespective of layer thickness. The minimum linear energy density of 2.5 J/mm is considered to fabricate the continuous track formation for investigated layer thickness. From statistical analysis, it is observed that the laser power and scanning speed shows higher contribution on track width and remelting depth, respectively. Whereas, layer thickness shows a higher influence on track height and contact angle of single track as compared to laser power and scanning speed. In 125 μm layer thickness, the volume of material melting is increased which encourages the gravity effect to deform the melt pool and produces larger track width compare to 100 μm layer thickness. Further, the cell spacing is gradually increased with layer thickness resulting increase in the solidification period. The shape controllability of the single track is significantly increased with layer thickness, but as keeps on increasing layer thickness due to the larger volume of molten metal, the melt pool losses ability to maintain convex shapes. An Artificial Neural Network (ANN) model is developed to understand the relationship between the LPBF process parameters and single track geometrical characteristics to predict the responses for a wide range of process parameters. The multiple response neural network model shows excellent agreement with experimental results with R2 value greater than 0.95.

Optimization of functional performance of additively manufactured cobalt‑chromium‑molybdenum alloy for dental implant applications

Improper selection of Laser Engineered Net Shaping (LENS) process parameters for the fabrication of cobalt‑chromium‑molybdenum (CoCrMo) alloy may result in poor quality components for dental implant applications. To solve the LENS fabrication challenge, this work utilizes response surface methodology (RSM) to investigate the influence of LENS deposition variables on the microstructural and mechanical performance of the manufactured samples for dental implant applications. Analysis of statistical data demonstrated that microhardness and porosity were both significantly influenced by laser scan speed and powder feed rate, while surface roughness is impacted substantially by laser scan speed and laser power. The analysis of the responses revealed that the optimum factors were at a scan speed of 5.3 mms−1, powder feed rate of 4.748 gmin−1 and laser power of 386.896 W to give surface roughness, porosity, and microhardness responses of 8.7775 μm, 0.06 %, and 387.4286 HV, respectively. The models revealed a strong interaction between the actual experimental data and RSM-predicted responses. The results of this research can serve as a guide for determining suitable LENS input factors for the manufacture of dental implants.

The effects of 3D printing parameters, structural design and post-processing on the mechanical properties and corrosion resistance of SLMed ZK60 porous scaffolds

High-quality porous Mg alloy scaffolds show promise in repairing large segmental bone defects. In this study, the authors prepared porous ZK60 scaffolds using the selective laser melting (SLM) method with three different model structures: Gyroid (G), Diamond (D), and Dodecahedral (Do). The researchers investigated the structural refinement, mechanical properties, and corrosive properties of SLM-ed ZK60 by adjusting the 3D printing parameters, specifically the scanning speed and laser power. The results show that, with optimized process parameters of a scanning speed of 400mm/s and a laser power of 110W, the relative density of the prepared samples was higher than 97%. After post-processing with electrolytic polishing, the G model scaffolds showed a smooth structural transition and the largest surface area compared to the other two models. The electrolytic polishing treatment also improved the structural refinement of the 70% designed porosity, with an error of only 4.3%. Additionally, the Do model scaffolds exhibited the best mechanical properties, with a yield strength of up to 24MPa and an elastic modulus of up to 425MPa. Furthermore, after coating treatment, the corrosion rate decreased from 5.67mm/year to 1.34mm/year after 48hours. These results demonstrate the potential of SLM-ed porous scaffolds for biomedical applications.

Performance and compensation method of first-order liquid crystal beam-steering system under continuous wave laser irradiation

The effects of laser irradiation thermal deposition on the performance degradation of liquid crystal (LC) devices in high-power laser systems are extremely vital. In this study, the first-order beam-steering system (FBS) was developed using a passive liquid crystal polarization grating (LCPG) and liquid crystal adjustable wave-plate (LCAW). The LCPG was prepared by holographic exposure technology, and the LCAW was prepared using the standard LC cell preparation process. We investigated the influences of diffraction efficiency of FBS under a 1070-nm continuous-wave (CW) laser irradiation. The energy is concentrated in the −1st order at first. When the half-wave retardation was reached, all the energy is concentrated in the +1st order (∼97 %), and the beam is deflected. Once the phase retardation decreases below the half-wave retardation, the energy gradually reconcentrates in the −1st order. When the LCAW fails, the diffraction the energy is refocused to the −1st order by the LCPG. The results indicated that both thermal deposition and driving voltage reduce the phase retardation of the LCAW, generating a variation of energy between in ±1st orders. By reducing the driving voltage, this half-wave retardation can be recovered under a certain half-wave voltage and laser power density, and the diffraction efficiency of the +1st order can be compensated to ∼97 %. If the reduced phase retardation is not less than half-wave, the FBS can still be modulated in high-power continuous lasers. Our research provides a reference for the development of beam-steering technology based on LC materials in high-power laser systems.

Investigation on the joining process and strength of laser circle welding between Al5052 and CFRP dissimilar materials

Laser welding is an effective approach to joining metal and composite. In the present research, laser circle welding was proposed to join the Al5052 sheet and PA6-CFRP as the first try. A process window was suggested according to the welding results and joint appearance. Single lap shear test was employed to evaluate the mechanical performance of welded joints under different welding conditions. The cross-section and fracture surface were subjected to multi-scale characterizations to subdivide the joining zone and understand the joining process. The result showed that 10 sets in 18 groups of welding parameters can achieve successful bonding. The welding results can be classified into four categories: non-connected, aging-failing, effective-joining and burn-through. The joining zone of laser circle welding was divided into three subregions. The adhesive zone (AZ) presented an interfacial fracture while the local failing passed through plastics basement in cohesive (CZ). The overheating of CFRP generated decomposed zone (DZ). The signal peak of O-C=O bond disappeared in the entire joining zone on CFRP sheet and the intensity of carbide was significant in DZ. The laser circle welded joint presented brittle and ductile fracture modes, which were related to the joining zone component. The joining strength can reach about 656 ± 22 N, 2135 ± 331 N and 3223 ± 257 N under one-circle, double-circle and three-circle scanning, respectively. Increased scanning numbers can decrease the required laser power and improve joining strength by extending heating time, while it also increased the risk of burn-through.

Upconverting Nanoparticles Coated with Light-Breakable Mesoporous Silica for NIR-Triggered Release of Hydrophobic Molecules.

Upconverting nanoparticles (UCNPs) doped with Yb3+ and Tm3+ are near-infrared (NIR) to ultraviolet (UV) transducers that can be used for NIR-controlled drug delivery. However, due to the low quantum yield of upconversion, high laser powers and long irradiation times are required to trigger this drug release. In this work, we report the one-step synthesis of a nanocomposite consisting of a LiYbF4:Tm3+@LiYF4 UCNP coated with mesoporous UV-breakable organosilica shells of various thicknesses. We demonstrate that a thin shell accelerates the breakage of the shell at 1 W/cm2 NIR light exposure, a laser power up to 9 times lower than that of conventional systems. When the mesopores are loaded with hydrophobic vitamin D3 precursor 7-dehydrocholesterol (7-DH), shell breakage results in subsequent cargo release. Its minimal toxicity in HeLa cells and successful internalization into the cell cytoplasm demonstrate its biocompatibility and potential application in biological systems. The tunability of this system due to its simple, one-step synthesis process and its ability to operate at low laser powers opens up avenues in UCNP-powered NIR-triggered drug delivery toward a more scalable, flexible, and ultimately translational option.

Theoretical and Experimental Analysis of the Effect of Vaporization Heat on the Interaction between Laser and Biological Tissue

A theoretical model, based on the classical Pennes’ bioheat theory, incorporating various boundary conditions, was established and compared to analyze the influence of the latent heat of vaporization via simulation. The aim was to elucidate the extent of its influence. The thermal damage rate, governed by the vaporization heat of biological tissue, is introduced as a key factor. Functional relationships between temperature and incident laser power, spatial position, and time are derived from the classical Pennes’ bioheat equation. According to the theoretical model, numerical simulations and experimental validations are conducted using Comsol Multiphysics 6.0, considering the tissue latent heat of vaporization. The model incorporating the latent heat of vaporization proved more suitable for analyzing the interactions between laser and biological tissue, evident from the degree of fit between simulated and experimental data. The minimum deviations between theoretical and experimental observations were determined to be 2.43% and 5.11% in temperature and thermal damage, respectively. Furthermore, this model can be extended to facilitate the theoretical analysis of the impact of vaporization heat from different primary tissue components on laser-tissue interaction.

Zr-based bulk metallic glasses in PBF-LB/M: near-polished surface quality in the as-built state

AbstractThis study investigates the relationship between varying contour scanning parameters and their impact on both surface characteristics and mechanical performance of the glass-forming Zr59.3Cu28.8Al10.4Nb1.5 produced via PBF-LB/M. Near-polished surface states with Ra values below 1 µm were achieved. The study identifies increased laser power as a key factor in reducing the surface roughness, while repetitive scanning exhibits only marginal improvements in surface quality. Partial crystallization on the surface of the amorphous samples is found on the as-built surfaces. However, it appears to be confined to depths below 50 µm. Impressively, the material showcases large mechanical strength in the as-built condition, evidenced by a high flexural strength of 2.2 GPa combined with approximately 1% plastic deformation. These findings offer initial insights into optimizing additive manufacturing processes for BMGs, guiding the enhancement of both surface quality and mechanical robustness in Zr-based metallic glass fabricated via PBF-LB/M techniques.

Experimental Study on Parameters Optimization of Selective Laser Melting 316L Stainless Steel Based on the Response Surface Methodology

Abstract The use of 3D printing technology can prepare flexible and varied special-shaped complex structures while realizing resource-saving and cost reduction. For this purpose, a 316L stainless steel sample was formed by selective laser melting technology, and the quality of samples was optimized by the Box–Behnken surface response method. Taking the surface roughness Sa as the response value, a regression analysis of four parameters of selective laser melting (laser power, scanning speed, scanning spacing, and scanning strategy) was designed using design expert software. The results showed that the scanning spacing and scanning speed have the greatest influence on the surface roughness, while the laser power and scanning strategy have no significant influence on the surface roughness. Meanwhile, the established surface roughness response surface model is effective and can be used for quality optimization of 316L structural trim. When the laser power was 185 W, the scanning speed was 615 mm/s, the scanning spacing was 110 μm and concentric scanning strategy was adopted, the surface adhesion powder was less, and the minimum surface roughness Sa was 9.001 μm.

Taguchi-Grey relational analysis driven multi-objective optimization of weld bead geometry and hardness in laser welded Ti6Al4V Alloy

AbstractThis study used Taguchi-based Grey relational analysis to optimize the bead geometry (bead width and length) and the hardness of laser welded 3 mm thick Ti6Al4V alloy sheets joined using the butt configuration. Firstly, the L9 (32) orthogonal array, with varying laser power and welding speed, was employed to optimize the input parameters (bead length, width, and hardness). The Taguchi optimization showed that the welding speed and laser power have a significant effect on the hardness of the welds and that laser power has a significant impact on the bead length. Meanwhile, the welding parameters had little effect on the bead width. These results were further affirmed with the Analysis of Variance (ANOVA). The Grey relational multi-objective optimization shows the optimized parameters for all responses to be 3 kW laser power and 2.2 m/min welding speed. It is important to note that the combination of Taguchi and Grey relational analysis and ANOVA is useful in optimizing welding parameters to achieve suitable weld properties.

Raman Monitoring of the Electro-Optical Synergy-Induced Enhancements in Carbon-Bromine Bond Cleavage, Reaction Rate, and Product Selectivity of p-Bromothiophenol.

Electro-optical synergy has recently been targeted to improve the separation of hot carriers and thereby further improve the efficiency of plasmon-mediated chemical reactions (PMCRs). However, the electro-optical synergy in PMCRs needs to be more deeply understood, and its contribution to bond dissociation and product selectivity needs to be clarified. Herein, the electro-optical synergy in plasmon-mediated reduction of p-bromothiophenol (PBTP) was studied on a plasmonic nanostructured silver electrode using in situ Raman spectroscopy and theoretical calculations. It was found that the electro-optical synergy-induced enhancements in the cleavage of carbon-bromine bonds, reaction rate, and product selectivity (4,4'-biphenyl dithiol vs thiophenol) were largely affected by the applied bias, laser wavelength, and laser power. The theoretical simulation further clarified that the strong electro-optical synergy is attributed to the matching of energy band diagrams of the plasmonic silver with those of the adsorbed PBTP molecules. A deep understanding of the electro-optical synergy in PBTP reduction and the clarification of the mechanism will be highly beneficial for the development of other highly efficient PMCRs.

Photoluminescence studies of the charge states of nitrogen vacancy centers in diamond after arsenic ion implantation and subsequent annealing

In this work, nitrogen vacancy (NV) centers of high nitrogen diamond implanted with arsenic ions were investigated by photoluminescence spectroscopy. The transition of the NV center charge state was discussed by the regularly changing laser excitation power and measurement temperature following high-temperature annealing. After high-temperature annealing, the amorphous layer generated by arsenic ion implantation is transformed into a graphitization layer, resulting in a decrease in the NV yield. The electric neutral NV (NV0) center and negatively charged NV (NV−) center are affected by both radiation recombination and Auger recombination with increasing laser power. Accompanied by the increasing measurement temperature, the intensities of NV centers gradually decreased and eventually quenched. In addition, the charge states of NV− and NV0 centers were undergoing a transition. The zero phonon line positions of NV centers were also red shift, it was attributed to the dominant role of electron–phonon interaction in the temperature-dependent displacement of diamond energy gaps. The full width at half maxima of NV center were broadened significantly at higher temperatures.

Researches on the continuous-wave infrared laser-assisted-load icebreaking

Abstract In this paper, a novel continuous-wave infrared laser-assisted load icebreaking method for large-sized ice blocks is put forward, which employs a laser multipoint irradiation approach. By strategically changing the mode of deployment points, interlocking cracks and melt holes are generated within the ice. This process effectively weakens the strength of ice, thus decreasing the difficulty of icebreaking. Based on the interaction mechanism between laser and ice, a mathematical model describing the evolution of the local temperature and stress of ice during continuous-wave infrared laser irradiation is established. The effects of deployment mode, laser irradiation time and laser power on the temperature and stress fields are analyzed based on numerical simulation. The impact of laser multipoint irradiation on the superposition of the stress between adjacent deployment points is revealed. On this basis, the experiments of continuous-wave infrared laser-assisted static-load icebreaking and impact-load icebreaking are carried out with natural freshwater ice as the research object. The influences of deployment mode, laser irradiation time and laser power on the external force required for subsequent icebreaking and the final icebreaking effect are analyzed. The characteristics of continuous-wave infrared laser-assisted static-load and impact-load icebreaking are comprehensively compared. Ultimately, the conclusion that impact load is more suitable for laser-assisted load icebreaking is drawn. The outcomes of this study potentially provide a new perspective on the breaking of large-sized ice blocks in an efficient way.

Effects of process parameters and geometry on dimensional accuracy and surface quality of thin strut heart valve frames manufactured by laser powder bed fusion

AbstractLaser powder bed fusion (LPBF) is one of the most popular metal additive manufacturing technologies, which has found its applications in high-value sectors such as aerospace and biomedical devices. Some recent studies on the LPBF of stents have demonstrated its feasibility in the fabrication in thin strut structures including heart valve frames, as used in transcatheter aortic valve implantation (TAVI) for the treatment of severe aortic stenosis. The state of the art method of laser cutting TAVI frame limits the scope for novel concepts which are made possible by additive manufacturing. However, the surface quality and dimensional accuracy of LPBF parts are lower than that produced by laser cutting. To start the development of new TAVI concepts, the feasibility of manufacturing thin frames by LPBF has been investigated based on the SAPIEN 3 frame by Edwards Lifesciences. In this study, simplified frames with strut size from 0.3 to 0.5 mm have been successfully manufactured. The effects of strut size, strut angle, laser power and scan speed on the dimensional accuracy and surface quality were systemically studied. In addition, a representative SAPIEN 3 frame was manufactured and assessed with high-resolution X-ray CT scans. Good overall dimensional accuracy and low porosity were obtained for the SAPIEN 3 frame. However, inclined struts were found to have relatively low dimensional accuracy and poor surface quality.

Multiphonon-coupling yellow laser in Yb:La2CaB10O19 crystal

Yellow lasers at 590 nm have many extensive applications in our daily life, but extremely difficult to attain by traditional solid-state laser technology, owing to the absence of highly-efficient transition channels at this spectral range. In this work, we proposed a cooperative lasing mechanism to obtain the yellow light emission, with multiphonon-assisted electronic transitions and phase-matched frequency-doubling. Based on the predictable configurational coordinate model, we can calculate the multiphonon-assisted emission step-by-step. Using Yb3+-doped La2CaB10O19 crystal as an example, it is capable of producing yellow laser at 581–590 nm, with a maximum output power of 4.83 W and a high slope efficiency of 31.6%. To the best of our knowledge, it represents the highest power of solid-state yellow laser realized in one single crystal pumped by a laser diode. This power scaling can be assigned to the amplified phonon-assisted emission beyond the fluorescence spectrum, and optimized crystal angle for phase-matching condition. Such a compact, low-cost, and high-power laser device, provides an alternative candidate for the spectral “yellow-gap” where no practical solid-state laser exists at present.

A GaN-based SOI plasmonic nanolaser design with high-output power

Due to its unique optical and electrical properties, gallium nitride (GaN) exhibits great promise for nanolaser cavities. These characteristics include high electron mobility, wide bandgap energy, and a high refractive index. Moreover, GaN exhibits remarkable thermal stability, making it appropriate for high-power laser applications. The choice of active medium material can significantly impact the laser’s performance, including its wavelength, output power, and efficiency. This work designed and numerically demonstrated a GaN-WG built-in Si O2 substrate with an input and output Si-waveguide nanolaser. These nanolasers lase multi-output wavelengths in both directions (forward and backward) at 1680 and 1750 nm, respectively. The pump power is 800 nm. The GaN-waveguide material, when used in nanolaser cavity design, gives many different advantages, like concentration of the Gaussian envelope and improved polarization depending on rate (PDR). Increasing lasing efficiency by 76.6% in the forward direction and 96.7% in the backward direction. Get a low lasing threshold of approximately 200 μW in the forward direction and 180 μW in the μW backward direction. Finally, improved the output laser power in both directions (460 μW and 600 μ W) in the forward and backward directions, respectively.

Prediction of mechanical properties of LPBF built part based on process monitoring and Gaussian process regression

As a highly promising technology in additive manufacturing, the laser powder bed fusion has only limited application due to its low reproducibility. In this study, the image information of the 316L specimen after laser scanning and powder paving of each layer was acquired by a complementary metal–oxide–semiconductor industrial camera. The important features were selected, extracted and quantificated by analyzing the tensile test results. Finally, combined with the laser power, the quantified features were as input of a Gaussian process regression model based on optimization algorithm of grid search to predict the tensile strength of 316L specimen. The results show that the quantized image features have a significant improvement on the regression effect, and the coefficient of determination (R 2) is improved from 63% to 90.57% compared to using only the laser power as input.

Secondary electron emission reduction from boron nitride composite ceramic surfaces by the artificial microstructures and functional coating

Boron nitride-silicon dioxide (BN–SiO2) composite ceramic is a typical Hall thruster wall material, and its secondary electron emission (SEE) property dominates the sheath characteristics inside the thrusters. Lowering the SEE yield (SEY) of the wall surface can remarkably improve the sheath stability of Hall thrusters. To accomplish the SEY reduction for BN–SiO2, artificial surface microstructure and surface coating technologies are employed. The morphology analysis demonstrated the shape and feature sizes of the microstructure could be largely controlled by adjusting the laser etching parameters. Then we realized an increasingly significant SEY reduction for BN–SiO2 as the average aspect ratio of the microhole increases. The microstructures showed a remarkable SEY reduction when the laser power was 10 W and the scanning cycle was 50. In this case, the SEY peak values (δ m) of the two BN–SiO2 samples with mass ratios of 7:3 and 6:4 decrease from 2.62 and 2.38 to 1.55 and 1.46 respectively. For a further SEY reduction, a sputtering process was employed to deposit TiN film on the microstructures. The results showed that the TiN coating of 246 nm thickness reduced the δ m values of the two samples from 1.55 and 1.46 to 0.82 and 0.76, which achieved a notable SEY reduction compared to the original surface. Via simulation work, the SEY reduction achieved by microstructures was theoretically interpreted. Besides, by considering the effect of surface charging, the results of SEY converged to 1 with the irradiation pulse increasing presented. The research demonstrated a remarkable SEY reduction for BN–SiO2 ceramic by constructing surface microstructure and depositing TiN coating, which has application sense for low SEY engineering in specific working scenarios.

Low-temperature creep performance of additive manufactured Ti–6Al–4V

Abstract Additive manufacturing enables the fabrication of versatile and cost-effective metallic-alloy components from a digital data model. This study explores the prospects of selective laser melting (SLM), an additive manufacturing technique, for fabricating Ti6Al4V alloy components from Ti6Al4V alloy powders. Selective laser melting parameters, such as laser power, scanning speed, powder thickness, hatching space, and scanning strategy, are carefully selected through a series of experiments. The metallurgical characteristics (microstructure, grain orientation, and phase composition), microhardness, and creep performance of the as-fabricated specimens are tested and analyzed. The kinetics of phase transformation and rupture mechanism are determined using advanced instrumental characterization tools, such as field emission scanning electron microscope, energy dispersive X-ray spectroscope, X-ray diffractometer, and transmission electron microscope.

2 × 4 kW near-single-mode laser output assisted by an optimized bidirectional oscillating-amplifying integrated fiber laser configuration

Bidirectional output oscillating-amplifying integrated fiber laser (B-OAIFL) can achieve the two-ports laser amplification based on a single cavity, showcasing a promising prospect. In order to improve both the laser power and beam quality, we first simulate and optimize the stimulated Raman scattering (SRS) effect in the B-OAIFL. The simulation results show the SRS effect can be suppressed by optimizing the diameter as well as the length of the active fiber at different locations. With the guidance of theoretical and experimental analysis for the combined suppression of SRS and transverse mode instability (TMI), a near-single-mode B-OAIFL with 2 × 4 kW was demonstrated. Based on this foundation, we further devoted ourselves to the pursuit of the optimization of the structure and performance. The necessity of the configuration of side pump, which was initially introduced for its exceptional performance in stabilizing temporal chaos, was reevaluated in detail. With its negative impacts on efficiency improvement and SRS suppression were analyzed and verified, we removed this configuration and finally demonstrated a more simplified design with superior performance. A total bidirectional output of 8105 W was achieved, with an O-O efficiency of 79.6% and a near-single-mode beam quality of M A 2∼1.36,M B 2∼1.63. No signs of TMI were observed, and the signal-to-SRS suppression ratio was over 38 dB. The results still demonstrate a promising potential for power scaling based on this configuration and parameters.