Optimal Laser Power Research Articles

Surface generation of tungsten carbide in laser-assisted diamond turning

The removal mechanism of conventional cutting and in-process-heat laser-assisted cutting (In-LAC) of binderless polycrystalline tungsten carbide (WC) material is studied through systematic numerical analysis and experimental investigation. The proposed In-LAC model considers the accumulated thermal effect and the laser in-process-heat thermal boundary condition simultaneously. Results of molecular dynamics (MD) analysis are remarkably consistent with the experimental results qualitatively. The high-temperature nanoindentation test reveals the improved machinability of WC at an elevated temperature and provides a theoretical basis for cutting force reduction. A small Young's modulus measured at an elevated temperature presents a large elastic recovery value for the In-LAC model. The critical depth of no observed surface cracks of binderless WC increases from 26.6 nm to 106.3 nm, which can be attributed to in-process laser assistance. Furthermore, the In-LAC method is beneficial to avoid subsurface crystal bending and reduce subsurface damage in the MD model and the taper cutting sample subsurface. The existence of the laser annealing effect during the In-LAC process is directly proven by binderless WC cross-section transmission electron microscopy (TEM). According to the simulation analysis results and diamond turning chip morphology, the optimal laser power for polycrystalline WC ranges from 10 W to 15 W, which facilitates obtaining the surface finish of 4.66 nm in Sa and significantly improving the tool life.

Controlled pDNA Release in Gemini Cationic Lipoplexes by Femtosecond Laser Irradiation of Gold Nanostars.

The design of nanovectors able to overcome biological barriers is one of the main challenges in biomedicine. Gemini cationic lipids are considered potential candidates for gene therapy due to their high biocompatibility and capacity to condense nucleic acids safely in the form of lipoplexes. However, this approach presents difficulties regarding genetic unpacking and, therefore, control over this process becomes crucial to ensure successful transfection. In this work, gemini cationic lipoplexes were prepared in the presence of plasmonic gold nanostars (AuNSs) to afford a nanovector that efficiently releases plasmid DNA (pDNA) upon irradiation with near-infrared femtosecond laser pulses. A critical AuNSs concentration of 50 pM and optimized laser power density of 400 mW led to successful pDNA release, whose efficiency could be further improved by increasing the irradiation time. Agarose gel electrophoresis was used to confirm pDNA release. UV-Vis-NIR spectroscopy and transmission electron microscopy studies were performed to monitor changes in the morphology of the AuNSs and lipoplexes after irradiation. From a physicochemical point of view, this study demonstrates that the use of AuNSs combined with gemini cationic lipoplexes allows control over pDNA release under ultrafast laser irradiation.

Lasers for matrix‐assisted laser desorption ionization

Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry was introduced over 30 years ago, and it now plays a key role in several areas, including the characterization of microorganisms and tissue imaging. Lasers are, of course, a central component in MALDI mass spectrometers, but in commercial systems, the type of laser is determined by the instrument manufacturer, and for the operator, their only practical consideration is the selection of the optimal laser power, or fluence, that gives them the best quality spectrum for a given sample and matrix combination. In the Special Feature this month, Dr. Kermit K. Murray, Department of Chemistry, Louisiana State University, Baton Rouge, LA, provides a detailed discussion of the laser and its role in matrix-assisted laser desorption/ionization. Dr Murray's article includes a brief history of the development and use of lasers for ionization in mass spectrometry and he describes the wide range of lasers, wavelengths and instrument configurations, including dual-pulse configurations, that have been developed and evaluated during the evolution of MALDI mass spectrometry. For any mass spectrometrist using MALDI MS in their work, this Special Feature is essential background reading on one of the most important, but poorly understood components of this powerful analytical tool.

AgCl-based selective laser melting photocatalytic module for degradation of azo dye and E. coli

An innovative 3D printing procedure for producing a highly porous AgCl/Ag0 photocatalyst was developed and tested for its stability and degradability of azo dye (Orange II) and bacteria (Escherichia coli). The AgCl/Ag0 photocatalytic module was fabricated through selective laser melting (SLM), in which the AgCl powder was stacked in a thin layer (approximate average thickness of 30 μm) on a platform and melted by a high-power laser beam layer by layer until the 3D module was created. The melting process may cause AgCl to transform into other compounds, which may, in turn, reduce the activity of photocatalysts; for this reason, the optimal laser power and scanning speed for constructing an SLM module were investigated; they were determined to be 26 W and at 385 mm/s. This photocatalytic module effectively degraded azo dye and sterilized E. coli. The degradation of azo dye was performed under visible and UV light irradiation, and the degradation kinetics was first-order reactions. Furthermore, the azo dye degradability (95%) of this photocatalyst module persisted for five cycles in our experiment. The sterilization of E. coli was accomplished within a 135-min test, and the degradation kinetics was also first-order reactions. The photocatalytic module fabricated through SLM not only exhibited the ability to degrade contaminants in the water but also had durability and reliability after repeated use.

The Thermo-Mechanical Coupling Effect in Selective Laser Melting of Aluminum Alloy Powder.

In the selective laser melting process, metal powder melted by the laser heat source generates large instantaneous energy, resulting in transient high temperature and complex stress distribution. Different temperature gradients and anisotropy finally determine the microstructure after melting and affect the build quality and mechanical properties as a result. It is important to monitor and investigate the temperature and stress distribution evolution. Due to the difficulties in online monitoring, finite element methods (FEM) are used to simulate and predict the building process in real time. In this paper, a thermo-mechanical coupled FEM model is developed to predict the thermal behaviors of the melt pool by using Gaussian moving heat source. The model could simulate the shapes of the melt pool, distributions of temperature and stress under different process parameters through FEM. The influences of scanning speed, laser power, and spot diameter on the distribution of the melt pool temperature and stress are investigated in the SLM process of Al6063, which is widely applied in aerospace, transportation, construction and other fields due to its good corrosion resistance, sufficient strength and excellent process performance. Based on transient analysis, the relationships are identified among these process parameters and the melt pool morphology, distribution of temperature and thermal stress. It is shown that the maximum temperature at the center point of the scanning tracks will gradually increase with the increment of laser power under the effect of thermal accumulation and heat conduction, as the preceded scanning will preheat the subsequent scanning tracks. It is recommended that the parameters with optimized laser power (P = 175–200 W), scanning speed (v = 200–300 mm/s) and spot diameter (D = 0.1–0.15 mm) of aluminum alloy powder can produce a high building quality of the SLM parts under the pre-set conditions.

Effect of mass transfer channels on flexural strength of C/SiC composites fabricated by femtosecond laser assisted CVI method with optimized laser power

In this study, femtosecond laser assisted-chemical vapor infiltration (LA-CVI) was employed to produce C/SiC composites with 1, 3, and 5 rows of mass transfer channels. The effect of laser machining power on the quality of produced holes was investigated. The results showed that the increase in power yielded complete hole structures. The as-obtained C/SiC composites with different mass transfer channels displayed higher densification degrees with flexural strengths reaching 546 ± 15 MPa for row mass transfer channel of 3. The strengthening mechanism of the composites was linked to the increase in densification and formation of “dense band” during LA-CVI process. Multiphysics finite element simulations of the dense band and density gradient of LA-CVI C/SiC composites revealed C/SiC composites with improved densification and lower porosity due to the formation of “dense band” during LA-CVI process. In sum, LA-CVI method is promising for future preparation of ceramic matrix composites with high densities.

Optimization of the laser-assisted tape winding process using an inverse kinematic-optical-thermal model

A new inverse kinematic-optical-thermal (IKOT) model is introduced to control the process temperature in laser assisted tape winding and placement processes. The optimum time-dependent laser power distribution is obtained by employing a grid of independent laser cells while keeping the temperature of substrate and tape at the target temperature. Multi-layer cylindrical hoop winding with laser grids of 1 × 1, 28 × 1, and 28 × 11 and helical winding of a pressure vessel with laser grids of 22 × 1 and 22 × 11 are considered. It is found that the optimized laser power distribution pattern remains the same during the consecutive hoop winding process while the total power reduces to compensate the heat accumulation. A more non-uniform laser power distribution is obtained for the helical winding because the substrate curvature changes drastically at the dome section of the pressure vessel. The change in the optimum total laser power is found to be almost constant for the helical winding case. Finally, the IKOT model is evaluated by analyzing the effect of the computational parameters on the optimized process temperature.

Analysis of wear properties and surface roughness of laser additive manufactured (LAM) Ti and TiB2 metal matrix composite

Abstract Industrial revolution in engineering materials applications through additive manufacturing has influenced the steel application in engineering industry. Limitations of wear of carbon steel has called for research focus in improving steel quality in wear resistance. Metallurgical applications of heat treatment were less effective as issues of temperature control; grain boundaries were evident. Matrix composite materials of better mechanical properties have been made use of to complement existing steel. This research focuses on the use of titanium, and titanium boride composite through laser cladding of addictive manufacturing. The admix composites were ‘mixed at different mass ratio, laser power and scan rate. A computer aided design (CAD) of design expert 9 was used to design the optimized parameters for the experimental analysis. Thirteen runs of random parameters of varying laser power and scanning speed were executed. An optimized laser power of 1500 W and scan rate of 1.2 m/min were derived and utilized. Nanocomposites of Titanium and Titanium di boride was at ratio loaded and cladded on steel rail surface. Metallurgical characterization of microscopic and macroscopic view was carried out. Different microstructural evolution was studied and analyzed. The wear tests were carried out at different loads of 2 N, 5 N and 10 N, respectively. The wear volume and wear rate were calculated. The least wear rate and wear volume was at the 50/50 mix ratio. A correlation and relationship between the wear properties, surface roughness and composition were examined.

Recent Advances in the Laser Radiation Transport through the Head Tissues of Humans and Animals – A Review

Modern studies of the penetration of light into biological tissues is becoming very important in various medical applications. This is an important factor for determining the optical dose in many diagnostic and therapeutic procedures. The absorption and scattering properties of the tissue under study determine how deeply the light will penetrate into the tissue. However, these optical properties are highly dependent on the wavelength of the light source and tissue condition. This overview paper analyzes the transmission of light through different areas of human and animal head tissues, and the optimal laser wavelength and power density required to reach different parts of the brain are determined using lasers with different wavelengths by comparing the distribution of fluence, penetration depth and the mechanism of interaction between laser light and head tissues. The power variation in different regions of the head is presented, as estimated using Monte Carlo (MC) simulations. Data are analyzed for the absorption and scattering coefficients of the head tissue layers (scalp, skull, brain), calculated using integrating sphere measurements and inverse problem solving algorithms such as inverse MC (IMC) and adding-doubling (IAD). This study not only offered a quantitative comparison between wavelengths in terms of light transmission efficiency, but also anticipated the exciting opportunity for online, accurate and visible optimization of LLLT lighting parameters.

Thermal behavior and densification during selective laser melting of Mg-Y-Sm-Zn-Zr alloy: simulation and experiments

The temperature field and flow field during the selective laser melting (SLM) process of Mg-3.4Y-3.6Sm-2.6Zn-0.8Zr alloy were simulated by using a re-developed Fluent 17.0 commercial finite volume method (FVM). The surface tension, Marangoni convection, and the laser heat source with Gaussian distribution are taken into account. The effects of laser power and scanning speed on the temperature and the size of the molten pool are studied, and the influence of line energy density (LED) on the flow and densification behavior of the molten pool is also discussed. It shows that the temperature and the size of the molten pool are positively correlated with the laser power, and negatively correlated with the scanning speed. The LED affects the flow of the molten pool and the movement of the bubbles, thereby affecting the densification behavior. For an optimized laser power of 50 W and scanning speed of 0.4 m s−1, the bubbles can escape smoothly, the existence time of the molten liquid is 355.58 μs and a molded part with the optimal density (95.98 ± 1.4)% is obtained. The experimental and numerical simulation results are in good agreement. It is concluded that a laser power of 50 W, and a scanning speed of 0.4 m s−1 are the optimal process parameters.

Laser writing of CsPbBr3 nanocrystals mediated by closely-packed Au nanoislands

Metal halide perovskites have attracted great interest in recent years owing to their excellent luminescence properties. The low formation energy makes it possible to synthesize perovskites of different types via direct laser writing. Here, we report on the formation of metal halide perovskite (CsPbBr3) nanocrystals coupled to the surface plasmon resonances of gold (Au) nanoparticles by irradiating a polymer film doped with the precursors (CsBr and PbBr3) and coated on a thin Au film. The Au film, which is composed of closely-packed Au nanoislands deposited on a silica substrate, act as not only the absorber of 800-nm femtosecond laser pulses but also the heat source for synthesizing and annealing of CsPbBr3 nanocrystals. The formation of CsPbBr3 nanocrystals in the area of laser irradiation was confirmed by Raman scattering spectra measurements. In addition, closely-packed Au nanoislands are transformed into isolated Au nanoparticles which exhibit surface plasmon resonances at ~530 nm. The CsPbBr3 nanocrystals coupled to isolated Au nanoparticles emit two-photon-induced luminescence at ~513 nm, which is enhanced by the surface plasmon resonances through the Purcell effect. An optimal laser power for direct laser writing was determined and the decomposition of CsPbBr3 nanocrystals was observed if a large laser power was employed. Our results indicate the possibility for the formation and annealing of perovskite nanocrystals coupled to surface plasmon resonances by one-step laser writing and open new horizon for their practical applications in color display and optical memory.

The study on surface quality and tool wear on laser-assisted micromachining of β21s titanium alloy

An experimental study was conducted on laser-assisted machining of β21s titanium alloy to investigate the effects of input variables of laser-assisted micromachining (LAMM) and conventional micromachining (CM) on the surface quality of β21s titanium alloy. At the same time, the tool wear patterns of LAMM and CM were revealed, and the wear law of the tools under different laser parameters when cutting different distances was studied as well. The experimental results showed that an optimum roughness value of 0.132 μm was obtained at a laser power of 30 W, a cutting speed of 100 mm/s, and a cutting depth of 10 μm, reduced by 61.7% as compared to CM. On the other hand, during the LAMM and CM experiments, the flank wear of the tools was characterized by bonding wear, while the degree of tool wear was effectively reduced in LAMM. Meanwhile, the influence of cutting length and laser power on tool wear is obtained under the condition of constant cutting speed and cutting depth. In addition, in the process of LAMM, as the cutting length increases and other processing parameters remain unchanged, the optimal laser power is not constant. Increasing the laser power appropriately can effectively suppress tool wear.

Control of the microstructure formation in the near-net-shape laser additive tip-remanufacturing process of single-crystal superalloy

A successful near-net-shape tip-remanufacturing process of single-crystal (SX) turbine blades should sustain a monocrystalline nature in the restored zone. Laser additive manufacturing (LAM) technique shows the huge potential to faultlessly restore the damaged tip of SX turbine blades. In this study, the microstructure formation in the near-net-shape tip-remanufacturing process of SX superalloy is studied through LAM experiments and simulation. The results indicate that due to the asymmetric heat diffusion condition at the top surface edge of SX substrate, the increase of laser power destroys the symmetry of morphologic size and microstructure formation in the single-track bead with a rapidly increased melting depth at the left side. Disoriented grains at the right side of the sing-track bead multiply layer by layer, gradually irrupting the epitaxial-growth continuity of columnar dendrites and resultantly destroying the monocrystalline nature of remanufactured tip structure. The continuous forced cooling of substrate not only shrinks the bead morphologic size, but also inhibits the disoriented grains formation at the right side of the single-track bead by directionally enhancing the epitaxial-growth ability of columnar dendrites. With the optimized laser power 550 W and continuously cooling substrate to −20 °C, a near-net-shape remanufactured tip structure with completely SX microstructure is achieved. The results provide an effective method to control the microstructure formation in the laser additive tip-remanufacturing application of SX turbine blades via coupling adjusting the laser power and continuous substrate forced cooling.

P‐1: Development of High‐yield Laser Lift‐off Process for Micro LED Display

This paper reports our developments for Micro LED laser lift‐off which is a very important step in Micro LED mass transfer process. By selecting the temporary bonding material, optimizing laser power intensity and other process parameters, the yield of Micro LED laser lift‐off can reach 99.87% for more than 1500 LEDs. This technical developments is of great potential for promoting high‐yield mass transfer technology to realize commercial Micro‐LED displays.

P‐85: Development of High‐yield Laser Lift‐off Process for Micro LED Display

This paper reports our developments for Micro LED laser lift‐off which is a very important step in Micro LED mass transfer process. By selecting the temporary bonding material, optimizing laser power intensity, and using PSS structure, the yield of Micro LED laser lift‐off can reach 99% for more than 5000 LEDs. This technical developments is of great potential for promoting high‐yield mass transfer technology to realize commercial Micro‐LED displays.

Development of High‐yield Laser Lift‐off Process for Micro LED Display

This paper reports our developments for Micro LED laser lift‐off which is a very important step in Micro LED mass transfer process. By selecting the temporary bonding material, optimizing laser power intensity and other process parameters, the yield of Micro LED laser lift‐off can reach 99.87% for more than 1500 LEDs. This technical developments is of great potential for promoting high‐yield mass transfer technology to realize commercial Micro‐LED displays.

Development of thick SiC coating on thin wall tube of zircaloy-4 using laser based directed energy deposition technique

In the present study, optimization of various laser-processing parameters for the deposition of thick SiC coating on zircaloy-4 (Zry-4) tube is studied in view of the development of accident tolerant fuel clad material for current and future nuclear reactors with the enhanced safety. The SiC coatings are deposited using laser directed energy deposition (LDED). It is found to be quite challenging to deposit desired SiC coating on a thin (~400 μm) substrate of Zry-4 tubes due to either its excessive melting or damage. This is minimized largely by cooling the tube from inside by passing Ar gas (20 l min−1). It is observed that different processing parameters play a vital role on homogeneity, uniformity and defects-free SiC coatings as well as on the melting and oxidation of Zry-4 substrate. A uniform and homogeneous coating of SiC is deposited on Zry-4 at the optimized laser power density of 4.52 kW cm−2, powder feed rate of 2.71 g min−1and scan speed of 325 mm min−1. The interface between SiC coatings and substrate is characterized using different techniques such as optical microscopy, scanning electron microscopy and X-ray diffraction to access the homogeneity, uniformity, defects and to identify the different phases formed in the coated layer. Coated layer is found to be consisting of Zr(α), SiC, ZrSi2, ZrSi and ZrC types of phases and the same is also confirmed by the ThermoCalc(R) based ternary phase diagram. Further, the effect of processing parameters on substrate melting and the nature of SiC coating is explained by simulating the substrate temperature using COMSOL@ multi-physics. To the author's best knowledge, this would be the first study to report the laser directed energy deposition of SiC on Zry-4 alloy.

Enhancement of mechanical properties of metamaterial absorber based on selective laser sintering and infiltration techniques

In this study, a 3D printing technology, selective laser sintering (SLS), and infiltration techniques were used to prepare a complex three-dimensional metamaterial absorber with high performance. The raw carbonyl iron (CI) powders were coated by polyamide12 (PA12), where the dissolution-precipitation method was used to improve their uniformity. The coated powders were then printed by SLS. The influence of laser power on the relative density of the composites was studied, where 18W was thought as the optimal laser power. And the SLS samples were infiltrated by thermosetting epoxy resin (EP, E−44) to increase their relative densities and strength. Mechanical tests showed that the infiltrated composites have an ultimate tensile strength of 41.98 MPa, almost 15 times higher than those without infiltration. The final metamaterial absorber (MMA) exhibited the reflection loss below −10 dB in 2.7–18 GHz. The above results indicate that the fabricated processes proposed in this paper have great potential for the preparation of three-dimensional metamaterial absorbers.

The effect of laser power on the microstructure and wear performance of IN718 superalloy fabricated by laser additive manufacturing

In this study, Inconel 718 (IN718) superalloys were fabricated by laser additive manufacturing (LAM) under different laser power. The microstructure and precipitation phase of IN718 superalloys were examined by optical microscope (OM), X-ray diffraction (XRD), scanning electron microscope (SEM), and energy-dispersive X-ray spectrometer (EDS) methods. The results show that the micropores of the specimens decrease with the increasing laser power. Meanwhile, the morphology of Nb-rich Laves phase changed from skeleton-like to island-like, and the sizes reduced from 10 to below 2 μm. When the laser power of 1200 W is applied, the dense microstructure and the uniformly distributed Laves phase with smallest volume and quantity are observed. The dry sliding test is performed to record the coefficient of friction (CoF) and wear loss of IN718 superalloys, and then the wear surface is detected by a laser scanning confocal microscope (LSCM) and a SEM. The results indicate that the laser power played a crucial role in wear performance of the specimens. At an optimal laser power of 1200 W, a relatively stable friction state and the lowest wear rate of 1.355 × 10−3 mm3 N−1 m−1 are obtained during the wear process. Less debris and slighter plastic deformation are detected and the wear mechanism is abrasive wear and adhesive wear.

Effect of surface texture and ultrasonic on tensile property of 316L/PET dissimilar joints

316 L stainless steel (316 L) was successfully joined to PET as a result of laser lap welding from metal side. An excellent joint with a large interfacial bonding was achieved by optimizing laser power and pulse width. Effects of surface texture and ultrasonic on 316 L/PET joint strength were clarified. The results showed that mechanical and chemical bonding were the main connection methods of 316 L/PET joint. Mechanical anchoring effect was the key factor of surface texture to improve the joint strength. There were two positive effects for ultrasonic on 316 L/PET joint strength. On the one hand, the acoustic streaming effect improved the fluidity of PET melt and made it easier to fill the texture. On the other hand, ultrasonic cavitation reduced the bubble rate in the weld and generated high pressure. For received samples, the maximum tensile strength reached 45 MPa, which was close to 86.5 % of the strength of PET matrix.