Laser Power Density Research Articles

Characteristics of welding laser beam and its influence on weld forming coefficient

Laser welding is a very complicated process. At present, there is no systematic research on the relationship between welding parameters and forming coefficient. By studying the internal relationship between laser parameters and the characteristics of welding laser, laser beam indexes, such as focusing index, are defined. They are simplified to a few laser parameters so as to facilitate the study of the influence of welding parameters on the forming coefficient. The results show that material, assembly gap, laser power and welding speed have great influence on weld penetration. When the laser power density reaches 106J/cm2, the characteristics of deep penetration welding appear. Under the condition of constant clearance, the weld depth increases with the increase of t/b. The weld penetration increases with the increase of laser power and tends to be stable when the welding speed is 12mm/s. Different materials also have a certain influence on the weld penetration depth. Under the same conditions, X6CrNiTi1810 obtains greater penetration depth, indicating that physical and chemical properties of materials are also one of the factors affecting the penetration depth. The mechanism and condition of laser welding were analysed. The relationship between laser absorptivity of sheet surface and physical properties of the materials is also studied and then obtained. The study will provide theoretical guidance for laser welding process design and welding parameter selection of steel plate.

Study of spatially confined copper plasma by probe beam deflection technique

In the last decade, laser induced plasma (LIP) has emerged as one of the most promising techniques for various applications. It is now commonly investigated using various expensive techniques. Probe beam deflection (PBD) is an inexpensive technique generally utilized to characterize the shock wave. In this work, the copper laser-induced plasma plume and shock wave are both investigated using PBD technique. The plasma is generated at atmospheric pressure using Nd:YAG laser at a low laser power density (0.8 GW/cm2). The contribution of the plasma plume components to the PBD signal is clarified in space and time. The spatial confinement effect by a metallic disk is also investigated. It approves the physical mechanisms responsible for the deflection signal. As well, the spatial distribution of the weak shock wave velocity is considered.

Bifunctional upconverting luminescent-magnetic FeS2@NaYF4:Yb3+,Er3+ core@shell nanocomposites with tunable luminescence for temperature sensing

Multifunctional core@shell type FeS2@NaYF4:Yb3+,Er3+ nanocomposites emit bright, color tunable UC photoluminescence and magnetic activity. We confirmed optical temperature sensing capability and rarely reported sensing of the laser power density.

Thermodynamic study of molten pool during selective laser melting of alsi10mg alloy

A study of the thermodynamic behavior during the Selective Laser Melting process of AlSi10Mg alloy was conducted using a combined numerical simulation and experimental approach. A multiphase flow model incorporating gas-liquid-solid phases was established. The numerical simulation results aligned well with experimental findings, affirming the reliability of the numerical model. Insufficient and excessive laser power densities respectively led to incomplete fusion defects and spherical pore defects. The evolution of the melt pool was primarily influenced by recoil pressure, Marangoni force, and surface tension, resulting in keyhole formation, convective flow, and liquid surface oscillation as characteristic features of melt pool evolution. Solidification process and mechanical analyses revealed that the central region of the melt pool exhibited smaller temperature gradients and higher solidification rates. Properly increasing the scanning speed under suitable laser power conditions is more conducive to optimizing the solidification structure and enhancing the mechanical properties of SLM components. This study elucidates the thermodynamic evolution mechanism during the SLM process of aluminum-based alloys, providing theoretical support and guidance for optimizing the SLM process.

Optoelectronic properties of the Sb/III-Sb interface induced by laser photooxidation

Laser photooxidation is used to form a surface antimony layer on p-type GaSb and GaAs0.06Sb0.94. The emerged Sb/III-Sb interface is studied by a combination of the Raman and photoluminescence spectroscopy supported by Kelvin probe microscopy and atomic force microscopy. The laser power density controls the thickness and structure of the Sb layer. Laser photooxidation thickens the amorphous Sb layer that emerged after native oxide formation. The thickening decreases the bandgap photoluminescence intensity and increases surface band bending. Further increase in the laser power density forms a multilayered antimonene phase with a rhombohedral structure. The crystalline Sb layer decreases the surface band bending due to changes in the work function. For the crystalline layer, the PL intensity further decreases. The effective work function model explains the experimental results. Finally, the study shows that it is possible to modify surface optoelectronic properties with a submicrometer lateral resolution.

Rare earth-based halide double perovskite phosphor Cs2NaScCl6: Yb3+, Er3+ for multi-mode anti-counterfeiting application

At present, most fluorescent anti-counterfeiting technologies on the market are based on single-mode luminescence, which generally have poor anti-counterfeiting capabilities. Thus, developing multi-mode luminescent anti-counterfeiting materials that combine dynamic and static luminescence is a particularly urgent task. In this study, Cs2NaScCl6: Yb3+, Er3+phosphors were successfully prepared using the solvothermal method. These materials can emit bright green light under 980- or 1550-nm infrared laser irradiation and red light under 365-nm ultraviolet lamp illumination. In addition, by increasing the 980-nm laser power density from 20 to 309 mW/cm2, the luminescence colour can be adjusted from green to yellow, which equips this sample with an outstanding potential for dynamic anti-counterfeiting. Finally, screen printing technology was used to assess the sample's anti-counterfeiting capacity, and the sample was found to be an excellent anti-counterfeiting luminescent material.

Ce:LuAG transparent ceramics for high-brightness solid-state lighting: Fabrication and effect of Ce concentration

Compared to phosphor and phosphor in glass, phosphor ceramics have higher thermal properties, and are less prone to thermal quenching. (Ce,Lu)3Al5O12 (Ce:LuAG) has better thermal stability than most of the phosphors, such as (Ce,Y)3Al5O12 (Ce:YAG). However, the high melting point of Lu3Al5O12 (LuAG; up to 2010 °C) presents a great challenge in producing transparent ceramics (TCs), so a series of Ce:LuAG nanopowders with high sintering activity were prepared by the co-precipitation method and then used as initial materials to obtain x at.% Ce:LuAG (x = 0.05, 0.1, 0.2, 0.3, 0.35, 0.4, 0.5, 0.55, 0.6, 0.65, 0.7) TCs by vacuum sintering at 1775 °C for 10 h. Moreover, the luminous properties of typical Ce-doped LuAG phosphors were systematically investigated using excitation by light-emitting diodes or laser diodes (LEDs/LDs). The emission intensity of 0.4 at.% Ce doped sample is the highest among all TCs with Ce amount ranging from 0.05 to 0.7 at.% at room temperature. The photoluminescence intensity of 0.4 at.% Ce:LuAG only decreases by 12.5% from 25 to 225 °C. The 0.4 at.% Ce:LuAG based on 0.8 W LEDs and 1.1 W LDs has the optimum luminous flux of 71.5 and 113.7 lm and the luminous efficiency of 89.3 and 101.4 lm∙W−1, respectively. As Ce concentration increases, a decrease in the luminescence saturation threshold of TCs is observed with a blue laser power density of 2.5–36.9 W∙mm−2. A high-flux yellow-green light of 1166.9 lm is obtained from 0.1 at.% Ce:LuAG when excited with a high-power LD with an energy density of 36.9 W∙mm−2. This work explored the best Ce doping level in Ce:LuAG TCs, as well as the luminescence saturation threshold in remote laser lighting applications.

Lensless single-fiber ghost imaging

We demonstrate lensless single-fiber ghost imaging, which allows illumination and collection using a single optical fiber without a transmission-type system. Speckle patterns with relative coincidence degrees of 0.14 were formed by image reconstruction using improved differential ghost imaging. Employing fiber with a diameter of 105 µm, we achieved a spatial resolution of 0.05 mm in an observing area of 9mm2, at a working distance of 10 mm. Compared to a conventional neuroendoscope at a power density of 94mW/cm2, our imaging could be realized by extremely weak illumination at a laser power density of 0.10mW/cm2. Using our lensless single-fiber ghost imaging, with 30,000 speckle patterns and implementing a diffuser, we attained an average coincidence degree of 0.45.

Luminescence‐Refrigeration Module: Addressing Luminescence Saturation Challenges in Laser‐Driven Lighting

Abstract(Phosphor‐converted white laser diode (PC‐WLD) lighting shows promise for high‐luminance solid‐state illumination. However, luminescence saturation, stemming from optical and thermal factors and, hampers high‐power LD lighting progress. This study delves into the light‐thermal dynamics between lasers and Y3Al5O12:Ce3+ （YAG:Ce）transparent ceramic phosphors (TCPs). Over 48.9% of absorbed laser power generates heat, inducing luminescence saturation. To effectively handle heat dissipation, we introduce a Luminescence‐Refrigeration Module (LRM) comprising the YAG:0.005Ce3+ TCP and a thermoelectric cooler (TEC). The LRM raises laser power density saturation by 4.5 times, meeting high‐power laser lighting requirements. The designed LRM emerges as a groundbreaking strategy for advancing high‐power LD lighting devices.)

Broadening of He 1083nm, 388.8 nm, 501.6 nm, 587.5 nm, 667.8 nm, 706.5 nm, 728.1 nm lines and of H(α), H(β) and O 777 nm lines in atmospheric pressure helium

Helium atoms in electronically excited states are produced in atmospheric pressure parallel plate DBD helium plasma. Pressure broadening coefficients of several helium lines and of O(777 nm), H(β) and H(α) lines are deduced from the analysis of the spectral profiles of those lines. Absorption spectroscopy on He(3S) metastable atoms with a diode laser is used for 1083 nm He line. The influence of the laser power density on recorded absorption spectral profile is analyzed. For the other lines, emission from the plasma is analyzed with a very high resolution 2 m focal length spectrometer, working in the 2nd, 3rd or 4th diffraction order of the 1200 g/mm grating. Instrumental width ΔI ranges between 2.2 and 9.8 pm, depending on the spectral line. Knowing with high precision ΔI and the Doppler widths of the lines and the fact that the resulting Gaussian width of each line remains, at least, 4 times smaller than its Lorentzian width, permits to deduce the pressure broadening coefficients of helium 388.8, 501.6, 587.5, 667.8, 706.5, 728.1 and 1083 nm lines and of 777 O line with less than 3 % uncertainty for most of them. Observation of the forbidden 2p 1P1 –4f 1F3 component in the blue wing of the allowed 492.19 nm He(2p 1P1 –4d 1D2) line, indicates the presence of a static electric field E ≈ 5 ± 1 kV/cm during the 0.4 µs light collection time from the DBD. It is concluded that in pulsed plasmas, like DBD and plasma-jet, before deducing the plasma density from the homogeneous widths of H(β) or H(α) lines, one should ascertain that the static E-field in the gas is small enough during the light collection period for not inducing significant splitting of these lines. This would induce an extra broadening of the line, leading to an overestimated electron density.

Universal Approach to Integrating Reduced Graphene Oxide into Polymer Electronics.

Flexible electronics have sparked significant interest in the development of electrically conductive polymer-based composite materials. While efforts are being made to fabricate these composites through laser integration techniques, a versatile methodology applicable to a broad range of thermoplastic polymers remains elusive. Moreover, the underlying mechanisms driving the formation of such composites are not thoroughly understood. Addressing this knowledge gap, our research focuses on the core processes determining the integration of reduced graphene oxide (rGO) with polymers to engineer coatings that are not only flexible and robust but also exhibit electrical conductivity. Notably, we have identified a particular range of laser power densities (between 0.8 and 1.83 kW/cm2), which enables obtaining graphene polymer composite coatings for a large set of thermoplastic polymers. These laser parameters are primarily defined by the thermal properties of the polymers as confirmed by thermal analysis as well as numerical simulations. Scanning electron microscopy with elemental analysis and X-ray photoelectron spectroscopy showed that conductivity can be achieved by two mechanisms-rGO integration and polymer carbonization. Additionally, high-speed videos allowed us to capture the graphene oxide (GO) modification and melt pool formation during laser processing. The cross-sectional analysis of the laser-processed samples showed that the convective flows are present in the polymer substrate explaining the observed behavior. Moreover, the practical application of our research is exemplified through the successful assembly of a conductive wristband for wearable devices. Our study not only fills a critical knowledge gap but also offers a tangible illustration of the potential impact of laser-induced rGO-polymer integration in materials science and engineering applications.

Influence of Typical Technological Parameters on the Forming Quality of TA1 in Selective Laser Melting

As an emerging additive manufacturing technology with potential, selective laser melting (SLM) technology is one of the current mainstream additive manufacturing processes. Many complex conditions affect the quality of the SLM products, such as extremely short forming time, rapidly changing forming environment, and micron-level melting area. Numerical simulation and a printing experiment were used to study the influence of typical technological parameters on the forming quality of SLM products, where TA1 was used as the printing material. The typical technological parameters mainly considered laser power, laser scanning speed, hatch spacing, and laser energy density. Simulation analysis was based on the maximum temperature and the size of the molten pool, and the printing experiment was focused on the parameter design methods for typical processes and the forming quality of printed products. The results show the following: (1) An increase in laser power and laser energy density can significantly improve the forming quality. However, excessive input energy will lead to poor surface quality; (2) Scanning speed and hatch spacing need to be selected according to the size of the molten pool, which mainly influences the lap rate of the molten pool. The results of this study may provide some guidance for parameter setting and forming quality optimization in SLM manufacturing process.

Plastic deformation mechanisms and their threshold pressures of Ti6Al4V thin-walled structures induced by laser peen forming

To explore the minimum energy required for laser peen forming (LPF) and broaden the application scope of the process, plastic deformation behaviors of Ti6Al4V thin-walled structures induced by laser shock loading were investigated. LPF experiments varying laser power densities on thin-walled specimens with thicknesses of 0.5 mm and 3.0 mm were conducted. Finite element methods were used to analyze the evolutions of stress and strain with time to understand plastic deformation mechanisms, including the stress gradient mechanism (SGM) and shock bending mechanism (SBM). Experimental results showed that the threshold power density for LPF to deform a 0.5 mm-thick specimen is much lower than to deform a 3.0 mm-thick one. Simulated time/position diagrams of strain reveal that plastic deformation occurs once the shock loading acts on the material in the deformation mechanism of SGM. While in the deformation mechanism of SBM, plastic deformation does not occur until the whole section exhibits an overall bending, which presents an apparent sequential relationship after SGM. Finally, a criterion concerning the threshold pressure and thickness to determine plastic deformation of thin-walled structures under laser shock loading is proposed.

Strengthening effect of laser peening on fatigue performance and life extension of laser cladded IN718 nickel-based alloy parts

Strengthening effects of laser peening (LP) on fatigue life extension of IN718 nickel-based alloy parts repaired by laser cladding (LC) were investigated. Special attention was paid on the microhardness, residual stress, microstructures and fatigue performance. The results show that LP increases the microhardness and compressive residual stress of LCed samples and the induced severe plastic deformation closes the metallurgical defect. In addition, LP changes the microstructure of LCed parts, transforms a large number of columnar dendritic structures into cellular dendritic structures. The grains in the subsurface were refined and a high-density dislocation structure is produced as well. As a result, while compared with the matrix sample, the fatigue life of LPed sample with laser power density of 11.30 GW/cm2 is increased by 54.9 %. Finally, synergistic strengthening mechanism of LP on LCed IN718 nickel-based alloy parts through defective pore closure effect, high-amplitude residual stress, and microstructure evolution was revealed.

IOX1 epigenetically enhanced photothermal therapy of 3D-printing silicene scaffolds against osteosarcoma with favorable bone regeneration

Osteosarcoma (OS) is the third most common malignancy in adolescence. Currently, the treatments of OS confront great obstacles of tumor recurrence and critical bone defects after surgery, severely affecting the survival rates and living qualities of patients. Hence, it is urged to develop distinct biomaterials with both efficient tumor therapeutic and osteogenic functions. Although photothermal therapy (PTT) has aroused expanding interest, characterizing negligible invasiveness and high spatiotemporal adjustment, few studies discussed its drawbacks, such as thermal injury to adjacent normal tissue and exceeded laser power density, implying that focusing on sensitizing OS to PTT instead of simply elevating the laser power density may be a fresh way to enhance the PTT efficacy and attenuate the side/adverse effects. Herein, we successfully constructed 3D-printing silicene bioactive glass scaffolds with preferable PTT efficacy at the second near-infrared (NIR-II) biowindow and outstanding osteogenic biofunctions owing to the release of bioactive elements during degradation. Impressively, a histone demethylase inhibitor, IOX1, was introduced before PTT to sensitize OS to thermal therapy and minimize the side/adverse effects. This work offered a distinctive paradigm for optimizing the PTT efficacy of osteogenic scaffolds against OS with epigenetic modulation agents.

Effect of Laser Power on Nanocutting Mechanism of Silicon Carbide Ceramic: A Molecular Dynamics Simulation

AbstractSilicon carbide (SiC) ceramic is being increasingly applied in several engineering fields owing to its excellent saturation electron drift rate. Although much attention is paid to its material removal mechanism, producing a high‐quality SiC surface with a high material removal rate is still a challenging issue. Therefore, there is a need to investigate the material removal mechanism of SiC to improve the processing performance. In this study, the laser heating‐assisted nanocutting models are established using a molecular dynamics method. Then, a laser beam with various energies is irradiated onto the SiC. The influence of average laser power on the nanocutting mechanism of SiC is revealed in terms of the temperature of the machined region, cutting force, stress distribution state, subsurface damage, and tool wear. The results demonstrate that within the scope of this study, the using of laser irradiation methods has a positive effect on the machinability of SiC at the nanoscale, provided that the laser power density does not exceed the ablation threshold. Meanwhile, the results indicate that laser heating‐assisted methods have played an important role in suppressing tool wear. This study has significant theoretical and practical value in processing technology.

Correlation of Energy Density and Manufacturing Variables of AA6061 through Laser Powder Bed Fusion and Its Effect on the Densification Mechanism

Aluminum alloy processing via additive manufacturing (AM) technologies has increased in usage during the last decade. AM now enables manufacturing complex geometries not previously achieved through traditional manufacturing. Aluminum is usually processed using laser powder bed fusion (LPBF) technologies, which are used to manufacture metallic components of high geometrical complexity and dimensional accuracy and good mechanical, electrical, and chemical properties, which is why this technology is quite popular at industrial levels. To further develop quality control systems and new aluminum alloys using LPBF, there is a need to establish a predictive relationship between the parameters of the material. A study was carried out to investigate the relationship between energy density and process parameters such as laser power, scan speed, hatch spacing, scan pattern, and laser focus and its influence on the densification mechanism in additively manufactured components with aluminum alloys. AA6061 was selected due to its wide usage in different industries, given its low density and high mechanical performance. Relative density was analyzed using the Archimedes principle, and the quality and morphology of the AA6061 powder were analyzed through metallographic analysis. The process parameter selection was performed according to the best results obtained according to the laser power and energy density factors. The best manufactured samples had an energy density between 30 and 40 J/mm3, with relative densities above 99%.

Analysis of energy release rate of laser-induced cohesive bonding of carbon fiber-reinforced polyetherketoneketone thermoplastic composites

In this study, laser joining of carbon fiber/polyetherketoneketone composites with several patterns was investigated to achieve weight reduction without any mechanical fasteners. The laser beam concentrated the energy, and heat conduction in the through-thickness direction of heterogeneous carbon fiber-reinforced thermoplastics caused molecular diffusion at the joining interface. According to the double-beam cantilever test results, the maximum energy release rate (ERR) was 2.01 J/mm2, which was 900 % higher than that of epoxy adhesive joining using laser power densities in the range of 1.05–1.34 W/mm2. A higher ERR was achieved because the optimized laser joining pattern secured repetitive cohesive joining at the interface. Thus, a complicated and step-wise crack opening was observed, which interfered with the propagation.

Preparation of NCh-B and NCh-B-Ti nanocomposites and their ignition and combustion performances

To overcome the agglomeration and insufficient combustion of nano-boron (n-B) powders, this study successfully prepared two novel types of boron-based nanocomposites using the acoustic resonance technology, namely high-substitute nitrochitosan/nano-boron (NCh-B) with ratios of 1:3, 1:5, 1:7 and 1:9, and nitrochitosan/nano-boron powder/nano-titanium (NCh-B-Ti) with Ti contents of 5 wt%, 10 wt%, 15 wt% and 20 wt%. The structural morphologies, laser ignition and combustion properties of the composites were systematically investigated. The results suggest that the addition of NCh can significantly improve the dispersion of n-B. NCh-B exhibited a higher combustion performance than n-B, as evidenced by their ignition delay and flame areas. When the laser power density was 81 W, NCh-B5-Ti15% exhibited a combustion time and an ignition delay of 240 ms and 5.5 ms respectively, which were higher and lower than those of NCh-B5 (199 ms and 17 ms, respectively). Furthermore, NCh-B5-Ti15% displayed a lower ignition delay than both n-B powders (12 ms) and NCh-B (11 ms), as well as brighter flames and a larger combustion area. Therefore, the addition of n-Ti can promote the combustion of n-B powders, with the combustion products of NCh-B-Ti including H3BO3, B2O3, TiB2, and TiO. This study provides a new method for improving the ignition performance and combustion efficiency of n-B powders.

Thermally-stable AlN-based green and red composite ceramic phosphor wheel for LD lighting with high CRI

Phosphor conversion materials with excellent thermal stability and broad-spectrum is critical to obtaining laser lighting devices with high luminous flux and CRI. In this paper, high thermally stable green AlN-Lu3Al5O12:Ce (ASL) and red AlN–CaAlSiN3:Eu (ASR) composite phosphor ceramics were prepared by embedding phosphor into AlN ceramic matrix. With mass ratio of phosphor increasing, luminescence intensity and quantum efficiency gradually increased, and the maximum internal quantum efficiency reached 62.8 % and 78.9 % for ASL and ASR, respectively. Under laser exciting in reflection mode, ASL-20 and ASR-50 got the max luminous emittance of 2827.5 lm/mm2 and 268.7 lm/mm2 with a saturation laser power density of 60.4 W/mm2 and 16.7 W/mm2, respectively. The diffusion coefficient of Ca, Al, Si between AlN and CASN grains was 2–4 magnitude higher than that of Lu, O, N between AlN and LuAG grains, confirming facile solid solubility of AlN and CASN. Finally, luminescence performances of green-red color wheel fabricated by ASL and ASR were evaluated. When the area ratio of green to red was 2:1, the color wheel yielded the biggest CRI of 82.6. This work presents a facile strategy for fabricating high thermally stable AlN-based composite phosphor ceramic and its application in high-quality laser lighting and display devices.