Influence Of Laser Spot Size Research Articles

Influence of laser spot size on structure and properties of high-temperature CompoNIAL-M5-3 alloy produced by selective laser melting

The CompoNiAl-M5-3 high-temperature alloy based on nickel monoaluminide was obtained by selective laser melting (SLM) of a spheroidized powder with particle size in the range of 20 – 45 μm. The powder was manufactured using an integral technology including self-propagating high-temperature synthesis (SHS), briquette grinding, sieve and air classification followed with spheroidization of powder particles in a thermal plasma flow and ultrasonic purification of spheroidized particles from nanofraction. Using parametric studies, the SLM modes were tested on SLM 280H and TruPrint 1000 machines. Mechanical tests of the samples were carried out using the uniaxial compression scheme with the strain rate dε/dt = 10–4 s–1 in the temperature range 1023 – 1273 K. Scanning and transmission electron microscopy methods were used to study the influence of laser spot size on the evolution of microstructure and thermomechanical properties of the SLM-consolidated material in comparison with that obtained by hot isostatic pressing (HIP). The authors established the effect of HIP + HT (aging in vacuum) post-treatment on the structure and mechanical properties of the material. The yield strength at 1073 K of the alloy built on the additive machine with a laser spot diameter of 38 μm after SLM + HIP + HT was 500 MPa, which exceeded the yield strength of the HIP-samples by 220 MPa.

Influence of laser spot size and shape on ablation efficiency using ultrashort pulse laser system

Ultra-short pulsed laser systems provide high accuracy and high-quality materials processing for various kinds of applications. However, one of the highest industrial needs is to identify most efficient processes to achieve high throughput. In terms of ultra-short pulsed laser processing of metals, the specific removal rate (ablated volume per time and average power) shows a maximum value i.e. there exists an optimum fluence where the ablation process is most efficient. In this study the influence of spot size and shape (Gaussian and Top Hat) on the ablation efficiency on AISI 304 (1.4301) steel grade was examined using 10 ps and 350 fs laser pulses at wavelengths of 1064 nm and 1030 nm. The investigation revealed a significant drop of the specific removal rate with increasing Gaussian spot size for both pulse duration. While this behaviour is less pronounced for a Top Hat, showing just 8% decrease of specific removal rate for spot sizes bigger than 40 µm.

Spatial Resolution Measurements of C, Si and Mo Using LIBS for Diagnostics of Plasma Facing Materials in a Fusion Device**supported by the National Magnetic Confinement Fusion Science Program of China (No. 2013GB109005), National Natural Science Foundation of China (Nos. 11175035, 11475039), Chinesisch-Deutsches Forschungs Project (GZ768) and the Fundamental Research Funds for the Central Universities of China (Nos. DUT12ZD(G)01, DUT14ZD(G)04)

Recently, a laser-induced breakdown spectroscopic (LIBS) system has been developed for in situ measurements of the chemical compositions of plasma facing materials (PFMs) in the Experimental Advanced Superconducting Tokamak (EAST). In this study, a LIBS system, which was used in a similar optical configuration to the in situ LIBS system in EAST, has been developed to investigate the spatial distribution of PFM elements at 10−4 Pa. The aim of this study was to understand the nature of the spatial distribution of atoms or ions of different elements in the plasma plume and optimize the signal to background ratio for the in situ LIBS diagnosis in EAST. The spatial profiles of the LIBS signals of C, Si, Mo and the continuous background were measured. Moreover, the influence of laser spot size and laser energy density on the LIBS signals of C, Si, Mo and H was also investigated. The results show that the distribution of the C, Si and Mo peaks' intensities first increased and then decreased from the center to the edge of the plasma plume. There was a maximum value at R ≈ 1.5 mm from the center of the plasma plume. This work aims to improve the understanding of ablating plasma dynamics in very low pressure environments and give guidance to optimize the LIBS system in the EAST device.

Measurement of YAG laser absorptance by artificial diamond and cubic boron nitride

Based on the lumped parameter method, this study establishes an experimental scheme for YAG laser absorptance measurement. Laser absorptance is measured on artificial diamond and cubic boron nitride materials under different laser power levels at room temperature. This study presents an analysis of the influence of laser spot size, and number of repeated laser irradiation, heat-insulating material, etc. on absorptance. A theoretical parameter is provided for the process of laser truing and dressing of the corresponding abrasive wheel, and it is important for the analysis and modeling of laser-material interactions. Meanwhile, a reference for measuring the laser absorptance of material with the same physical performance is put forward.

Expansion dynamics and equilibrium conditions in a laser ablation plume of lithium: Modeling and experiment

The gas dynamics and atomic kinetics of a laser ablation plume of lithium, expanding adiabatically in vacuum, are included in a numerical model, using isothermal and isentropic self-similar analytical solutions and steady-state collisional radiative equations, respectively. Measurements of plume expansion dynamics using ultrafast imaging for various laser wavelengths (266–1064nm), fluences (2–6.5Jcm−2), and spot sizes (50–1000μm) are performed to provide input parameters for the model and, thereby, study the influence of laser spot size, wavelength, and fluence, respectively, on both the plume expansion dynamics and atomic kinetics. Target recoil pressure, which clearly affects plume dynamics, is included in the model. The effects of laser wavelength and spot size on plume dynamics are discussed in terms of plasma absorption of laser light. A transition from isothermal to isentropic behavior for spot sizes greater than 50μm is clearly evidenced. Equilibrium conditions are found to exist only up to 300ns after the plume creation, while complete local thermodynamic equilibrium is found to be confined to the very early parts of the expansion.

Evaluation of mismatch and non‐uniform illumination losses in monolithically series‐connected GaAs photovoltaic converters

AbstractThis work evaluates the influence of mismatch illumination on the performance of GaAs monolithically series‐connected photovoltaic converters under laser illumination. A theoretical model which takes into account nonuniform illumination, light spillage and mismatch losses is presented. The influence of laser spot size on the converter efficiency is also addressed.The laser spot size must be chosen in order to make a trade‐off between mismatch and nonuniform illumination losses, which predominate in a laser spot diameter smaller than the diameter of the device, and spillage losses, which predominate in a laser spot diameter larger than that of the device. For single photovoltaic converters, it is advisable to reduce the laser spot diameter to values to less than that of the converter. For multiple photovoltaic converters, especially if there is a considerable misalignment between the light source and the device, a spot diameter slightly larger than that of the device is recommended. Otherwise, mismatch losses could severely limit MPC performance. When the laser beam diameter equals the device diameter, and for a 5% misalignment, efficiencies of 55.0, 53.6 and 50.1% are envisaged, for two‐, three‐ and six‐sector multiple photovoltaic converters, respectively. Copyright © 2002 John Wiley & Sons, Ltd.