In order to study the mechanism of laser on aluminum alloy surface microstructure, the effect of laser scanning speed on aluminum alloy surface microstructure was revealed. In this paper, combining experimental and numerical methods, has thoroughly investigated the laser ablation process on aluminum alloy surfaces. The calculated results of the model agree well with the experimental results in some respects. By manipulating scanning speed and spacing, we successfully prepared distinct surface microstructures on the aluminum alloy. The findings indicate that scanning speed significantly impacts thermal diffusion and ablation depth, while control over scanning spacing positively shapes the surface microstructure's morphology. At wider scanning intervals, the thermal diffusion and internal thermal stress can induce a 'warping effect' and material removal. Optimizing these parameters is crucial for the highest quality micromachining outcomes.
As a key component in the laser system, contamination damage to the multilayer dielectric film reflector significantly limits the safe operation of the laser system. Stray light irradiation of the system on the metal structural components produced by the sputtering material is the main source of reflector surface contaminants. Mastery of stray light-induced contaminants behavior is essential for solving the problem of reflector contamination damage. In this study, the real process of sputtering contaminants induced by stray light irradiation of aluminum alloy in sealed chambers is experimentally simulated. The morphological characteristics, composition, and distribution pattern of the contaminants deposited on the reflector surface were analyzed. The influence of various types of contaminants on the damage performance of the reflector was investigated. Scanning electron microscopy measurements showed that the presence of carbonaceous organic contaminants and metallic aluminum particles on the surface of the samples resulted in localized bonding behavior. One-to-one damage threshold measurements showed that the composite contaminants severely degraded the performance of the reflector. These results fundamentally explain the source and physicochemical properties of the contaminants on the reflector surface in the laser system, reveal the mechanism of stray light-induced contaminants on the damage performance of the multilayer dielectric film reflector, and provide a theoretical basis for the clean debugging of the sealing cavities and the design of enhanced stray light irradiation resistance of the aluminum alloy materials.
The deleterious effects of organic contaminants on optical components are a major obstacle to high-energy laser systems, and laser ablation is an important means of removing contaminants. Nevertheless, irregularities or flaws created during the manufacturing process of optical element surfaces affect the absorption of organic contaminants while placing higher demands on laser ablation. Hence, it is imperative to comprehend the intricate interplay among surface roughness, contaminant absorption, and ablation in order to effectively confront the challenge of laser-induced damage. In this study, the three-dimensional morphology of the fused silica surface was simulated numerically employing the Weierstrass-Mandelbrot fractal function. On this basis, we developed a theoretical model through molecular dynamics simulations to gain insight into the adsorption process of dodecane organic molecules on fused silica surfaces. Building upon the obtained outcomes, the effect of surface roughness on the laser removal of the adsorbed model is comprehensively analyzed. The findings reveal that dodecane molecules tend to aggregate within enclosed crevices and irregular regions, resulting in heightened localized density. Additionally, an augmented substrate surface roughness diminishes van der Waals energy and pressure, thereby facilitating the elimination of contaminants. These findings are indispensable for deepening our understanding of the dynamic interactions involving lasers, fused silica, and organic contaminants, as well as providing valuable insights into effectively addressing the challenging issue of laser-induced damage.
Plasma has been widely used in the in situ removal of organic contaminants on the surface of large aperture optical components by physical bombardment and chemical reaction. Since the plasma is usually generated by ionizing gas through the electric field, the charged reactive species are accelerated to bombard the surface when passing through the surface sheath. After the organic contaminants on the surface of the optical components are completely removed, the surface film of the optical components may be eroded by long-time plasma irradiation. Therefore, the surface damage characteristics induced by plasma cleaning on optical components were studied to apply the technology of plasma in situ cleaning in the inertial confinement fusion facilities. Firstly, the effect of the amount of organic contaminants on the performance of optical components was investigated. Then, the influence of plasma cleaning time on the transmittance and wavelength peak of fused quartz optical components coated with sol-gel anti-reflection film was analyzed. The plasma cleaning experiments illustrated that the film thickness had a damage accumulation effect after the long plasma irradiation, and the surface pores gradually increased. The surface damage mechanism of plasma action was discussed. Finally, the research on the surface damage mechanism of sol-gel anti-reflective film during plasma cleaning lays a foundation for the realization of nondestructive in situ cleaning of optical components.
The surface of the gold film grating appeared to different degrees of carbon burning phenomenon under high energy laser irradiation, which resulted in the degradation of the grating performance. Thus, in this study, the main components and relative contents of organic contaminants in the wall and air at different positions in the chirped pulse amplification system were detected by gas chromatography and mass spectrometry. The organic molecules were volatilized from potential sources such as components and pump oil or dust produced by stray light irradiation of carbon-based materials. The contaminant C12H38O5Si6 was found at multiple sampling sites, indicating that the hydrocarbon molecules in the contaminant formed a chemical bond with the molecular structure of silicon and oxygen on the surface of the optical component. Compared to physical adsorption, this chemical bond adsorption is stronger and more difficult to remove. The effect of long-term vacuum organic contamination on the diffraction efficiency of the gold grating was not significant enough. On the contrary, organic residual contaminants were formed in the laser-irradiated area of the surface of the gold grating, and the diffraction efficiency was significantly reduced to two-thirds of the undamaged area. Many small organic molecules, particles and water molecules were deposited in the grooves on the surface of the gold grating, and carbonization occurs under the action of ultra-short pulse laser. A stress pit appeared in the center area of laser irradiation, causing damage to the surface of the grating.
Organic contaminants on optical components can degrade optical properties, thus limiting the energy enhancement of highpeak-
power laser systems. It is still challenging to remove organic contaminants on the SiO2 sol-gel antireflection film and
avoid damage. In this work, a low-pressure air plasma in-situ cleaning technique and a chemical reaction model of plasma
cleaning were proposed to study the removal of organic contaminants. The optical properties of sol-gel AR films suffered
from organic contaminants were evaluated by transmittance and laser-induced damage threshold, which recovered
completely after 5 minutes of plasma cleaning without damage. Meanwhile, the hydrophilicity of the surface and the
surface free energy were significantly increased after plasma treating. Surface composition analysis indicated that the CH
and C-C bonds were reduced considerably, while abundant C=C and C=O bonds were produced after plasma cleaning.
Optical emission spectrum analyzed the reactive species and its concentration in the air plasma as a reference for simulation.
The chemical interaction process of oxygen radicals with organic contaminants was simulated by reactive molecular
dynamics. The results can provide a guide for optical components in-situ cleaning.
As a kind of typical material for mechanical structure, stainless steel is often adopted in the high-power laser facility. Iron elements in stainless steel may play an important role in resisting the effect of laser ablation. Laser ablation of stainless steel or aluminium alloy can also cause metal particle contamination in high-power laser facility. The ablation processes on iron surface under laser irradiation are investigated with molecular dynamics (MD) simulation combined with two-temperature model. The trajectories of atoms in each region of single crystal iron under laser irradiation are analyzed in terms of the interaction between laser and iron. The simulation results show that atoms absorbing different energy show the macroscopic characteristics of different phases of single crystal iron. Studies have also shown that single atom and clusters of atoms may have a backlash effect on the material and cause stress waves. The propagation of stress waves is also analyzed. It is shown that the velocity of the stress wave is about 6.094 km/s. Ablation threshold of single crystal iron is determined by the movement of surface atoms under different laser energy densities and the simulation results show that ablation threshold of single crystal iron under femtosecond laser is 0.18 J/cm2. Meanwhile, it is also found that the instantaneous loading of laser energy has a greater effect on material ablation. This study can underpin for investigating the damage and contamination of precision mechanical component with stainless steel under the effects of laser irradiation.
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