大口径传输反射镜的研究进展

针对我国惯性约束聚变装置(ICF)对高性能传输反射镜元件的性能要求,探索了大口径传输反射镜制备涉及的关键技术与工艺。深入开展了K9玻璃坯片研制、光学冷加工、传输反射镜镀膜和激光预处理等方面的研究工作。提出了400mm口径K9反射类坯片精密退火工艺,形成了高精度平面加工技术路线;制备了低缺陷薄膜,并且建立了大口径光学元件预处理装置。最后,综述了大口径高性能传输反射镜研制方面的主要成果。研制的400mm口径传输反射镜在1053nm处以45°入射时,其表面粗糙度优于99.8%,面形PV值小于λ/3(λ=1 053nm),损伤阈值大于30J/cm2(5ns)。基于提出的技术研制的大口径传输反射镜已成功应用于我国神光系列高功率激光装置,有力支撑了我国大型激光装置的稳定运行。     

氧碘化学激光器腔镜表面缺陷的观察与分析

为了明确氧碘化学激光器腔镜损伤的原因,对腔镜表面的缺陷进行了研究。利用扫描探针显微镜观察了激光器腔镜表面缺陷,分析了腔镜表面微观形貌,讨论了常见缺陷的形状及成因。然后,建立了简化的带污染物腔镜的模型。利用COMSOL Multiphysics软件对环形光束辐照腔镜进行了仿真计算。最后,给出了缺陷大小、功率密度和腔镜表面温度的关系,分析了吸附层对腔镜熔融损伤的影响。计算结果表明:腔镜表面污染物大小不变时,激光辐照的功率密度越大,温度增长越快,薄膜表面越容易出现熔融损伤;腔镜表面污染物半径达到2.3mm时,腔镜薄膜即可出现熔融损伤。另外,吸附层吸收系数增加1%,腔镜最高温度增加约210K。本文所得结论可为分析腔镜损伤原因和制定腔镜更换依据提供参考。     

Laser brazing of a dissimilar joint of austenitic stainless steel and pure copper

In many industries, there are applications that require the joining of stainless steel and copper components; therefore, the welding of dissimilar stainless steel/copper joints is a common process. For this investigation, the optimal brazing conditions and suitable filler metals for laser brazing of stainless steel/copper lap joints were studied. Tensile shear force increases with increases in the laser spot diameter or in the laser irradiation angle, which is associated with increased bonding width; however, as bonding width approaches 2 mm, tensile shear force reaches a saturated value due to fracturing at the HAZ of the Cu base plate. In order to obtain joints with high tensile shear strength, laser brazing was optimized by using Cu–Si-based filler metal under the following conditions: laser power, 4 kW; spot diameter, 3 mm; laser irradiation angle, 80°; irradiation position shift, 0.6 mm; brazing speed, 0.30 m/min; and filler metal feed speed, 0.30 min. Concerning filler metals, it was found that the Ni–Cu type showed relatively large tensile shear force even at high welding speeds in comparison with those of the Cu–Si, Cu, Cu–Ni, Ni–Cu and Ni types, respectively.     

Development of gap sensing system for narrow gap laser welding

Narrow gap welding with an oscillation laser beam is one of the effective processes for thick plate welding. To put this welding process into practical manufacturing, a groove-sensing system using image processing for narrow gap welding with an oscillation laser beam is used. This developed system uses still images of the weld zone taken by a coaxial CMOS camera. It can recognize the position of the groove wall by analysing the brightness distribution in the still image. It can then control the oscillation width and the laser-irradiated area by calculating the groove width and the groove centre position. Some narrow gap welding experiments were performed to evaluate the performance of the developed system. The results revealed that the developed system is effective for narrow gap welding with an oscillation laser beam. Using this system, the narrow gap groove can be welded even if the groove width has changed during the welding process.     

石英玻璃飞秒激光微连接及其接头性能

飞秒激光的低热输入、极小热影响区的特点使其在微米尺度材料连接领域有明显的应用潜力。为研究飞秒激光进行玻璃连接的可行性及其接头性能,测定了其接头的拉剪强度并分析了接头断裂前后的形貌特征。证明了飞秒激光连接玻璃的可行性,并发现玻璃试样之间的间隙对飞溅有明显影响。拉剪试验测得的接头强度在6.4~40.4MPa之间。结果表明,在激光平均功率较大,焊缝间距较小的条件下,连接试样容易在母材中断裂,使得接头的强度相比于断裂在界面上的试样强度降低一半以上。     

基于激光视觉的角焊缝图像特征点提取

提出一种借助线激光从图像中提取角焊缝特征点的方法,克服了线激光在角焊缝表面的反光对提取光条中心线的影响,有效地识别出了角焊缝特征点. 首先,根据局部对比度区分实际光条与反光条纹,用阈值分割结合图像形态学方法分割出实际光条,并确定ROI区域;其次,根据光条截面的灰度分布提取光条中心点;最后,用迭代最小二乘法拟合分段光条中心线方程并确定角焊缝特征点. 结果表明,该方法能够快速准确地提取表面光亮角焊缝的亚像素图像特征点,在主频3.4 GHz的PC机上共用时0.35 s,能够满足焊接速度为0~25 mm/s的普通焊接设备的实时性要求.     

高强钢CO2激光-MAG复合焊接性能

为了研究CO₂激光-熔化极活性气体保护焊（MAG）复合焊接性能,采用CO₂激光和CO₂激光-MAG复合焊接590MPa级高强度钢,对其焊接接头的显微组织和力学性能进行了研究.结果表明,激光-MAG复合焊接的焊缝金属中,MAG电弧作用区主要为珠光体和贝氏体,激光作用区主要为马氏体;激光-MAG复合焊接的焊缝金属中Mo和Mn合金元素的分布具有不均匀性;激光和激光-MAG复合焊接的试件焊接接头拉伸性能完全满足要求,焊缝强度高于基体强度;激光-电弧复合焊缝金属在-60℃～+15℃试验温度范围内的冲击韧性比激光焊缝金属高;激光-MAG复合焊接焊缝金属硬度在250～400 HV之间,高于基体金属的硬度.     

Pulsed laser ablation in liquid synthesis of ZnO/TiO2 nanocomposite catalyst with enhanced photovoltaic and photocatalytic performance

In this work, we employed an impurity-free nanoparticle synthesis technique, known as pulsed laser ablation in liquid (PLAL), to integrate titanium dioxide nanoparticles (TiO₂ NPs) into zinc oxide nanorods (ZnO NRs) with varying relative proportions. The main objective of this integration was to enhance the charge carrier separation of photo-generated electron hole pairs during solar irradiation. For the synthesis process, an Nd:YAG laser at 532 nm wavelength was applied as an ablation source, along with deionized water as a solvent medium in which the precursor materials were dispersed prior to laser irradiation. The nanocomposites were characterized by X-ray diffraction (XRD), UV–vis absorption and in-situ Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HR-TEM) and field emission scanning electron microscopy (FE-SEM). The synthesized nanocomposites were primarily utilised in two applications: firstly, as a catalyst in the degradation of methyl orange (MO) and secondly, as photo-anode in dye sensitized solar cell (DSSC). Our research has demonstrated that optimal performance was obtained for the nanocomposite containing 10% and 90% (by weight) TiO₂ NPs and ZnO respectively, which we define as the ideal nanocomposite. Relative to pure ZnO, the photo-conversion efficiency of the ideal composite was improved substantially by 63.73%, whilst the photo-degradation rate was enhanced by 3 fold. The oxidation state and the microstructural of the segregated ideal nanocomposite confirms that oxygen vacancy defects were created when perfect surface integration occurs between TiO₂ and ZnO. Nonetheless, we believe that the performance enhancement is predominantly due to the excellent charge carrier separation and fast interfacial electron flow in this nanocomposite.     

Direct multipulse laser processing of titanium oxide–graphene oxide nanocomposite thin films

Nanocomposite thin films consisting of titanium oxide (TiO₂) nanoparticles (NPs) and graphene oxide (GO) platelets were deposited by a spin-coating technique. The obtained films were submitted to direct laser irradiation using a frequency quadrupled Nd:YAG (λ=266 nm, τ_FWHM≅3 ns, ν=10 Hz) laser source. The effect of the laser processing conditions, as laser fluence value and number of subsequent laser pulses incident onto the same target location, on the surface morphology, crystalline structure, and chemical composition of the TiO₂/GO nanocomposite thin films was systematically investigated. The laser fluence values were maintained below the vaporization threshold of the irradiated composite material. With the increase of the laser fluence and number of incident laser pulses melting and coalescence of the TiO₂ NPs into inter-connected aggregates as well as rippling of the GO platelets take place. The gradual reduction of GO platelets and the onset of anatase to rutile phase transition were observed at high laser fluence values.     

Precise micromachining of yttria-tetragonal zirconia polycrystal ceramic using 532 nm nanosecond laser

High quality micro-sized steps and blind hole structures without microcracks, chips or spatter deposition were machined on yttria-tetragonal zirconia polycrystal (Y-TZP, 3 mol% yttria) by nanosecond laser (wavelength=532 nm, pulse width ~6 ns). The diameter of blind hole is 500 μm and each step is 500±10 μm wide and 100±5 μm deep. The 1.35 mm³/min removal rate and the smooth machined surface with Ra=2.824 μm roughness depicting the high precise and efficient processing were achieved. The ablation characteristics of nanosecond laser process of Y-TZP ceramic were also studied. Based on the study, a reasonable design of the processing path for micromachining of a finer embedded step with 24±2 μm width (smaller than the 60 μm focused spot size) around the inner-wall of a 2×2 mm² cavity was developed. These results and discussion offer new possibilities in the manufacturing of bio-ceramic products by nanosecond laser with high processing quality and efficient.