During laser tube bending, a laser beam is used to produce non-uniform thermal strain leading to permanent bending without hard tooling or external forces. The advantages of laser tube bending include flexibility especially in multi-axial bending, no spring-back, and no wall thinning at the extrados. However, laser tube bending is currently impractical to be applied due to small bending generated at each laser scan. The advent of the high power direct diode lasers with a rectangular beam has provided potential to improve bending efficiency but requires a new set of problems to be addressed. In this thesis, four scanning schemes for tube bending, including point-source circumferential scanning, pulsed line-source axial procession, line-source axial scanning without and with water cooling are numerically investigated based on a coupled thermo-mechanical model using finite element method and compared in terms of bending deformation, input energy, cycle time and characteristics of deformed tubes. The influences of important parameters such as beam coverage, scanning velocity and cooling offset on the deformation are also investigated.;Laser cleaning is a process in which surface contaminants are ablatively removed by a pulsed laser without damaging the substrate surface. Due to its selectivity, controllability, environmental-friendliness and flexibility, laser cleaning is a promising alternative in microelectronic cleaning, art restoration and other applications. The removal of copper oxide from copper, the most widely utilized metal in the microelectronic field, is investigated. The chemical distribution and film thickness of copper oxide are characterized using X-ray photoelectron spectroscopy and ellipsometry. The effects of pulsing parameters such as laser intensity, pulse number and repetition rate on the successful laser cleaning are experimentally and numerically investigated, where a two-dimensional axial symmetric model is utilized to more accurately model laser ablative cleaning of copper oxide.;In restoration of stone artwork, it is important to preserve the aesthetic value of stone. Discoloration of the stone, say, marble, after cleaning hinders the potential of laser stone cleaning. The mechanism of discoloration is proposed from the viewpoint of thermochemical reactions. The reduction of iron oxides by graphite in an encrustation plays a key role in determining the surface color of cleaned stone. The kinetics of the thermochemical reactions are analyzed with a laser ablative cleaning model including reaction heats. The thermochemical reactions are also verified indirectly with experiments. The effects of fluence levels on the discoloration of marble cleaned using 355nm laser wavelength are comparatively studied. The effects of thin liquid layer covering the encrustation are also experimentally and numerically investigated. A two-dimensional axial symmetric model is proposed to simulate changes in temperature, liquid volumetric fraction and vapor pressure in the irradiated encrustation considering conservations of mass, momentum, and energy. Three liquids with different thermodynamic properties, that is, distilled water, ethanol and acetone, are considered in the thesis, along with their effect on the surface color of cleaned marble. The chemical components of marble surfaces are characterized through surface enhanced Raman spectroscopy. The surface color is measured with a chromameter using a 1976 CIE L*a*b* color system.
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机译：在激光管弯曲过程中，激光束用于产生不均匀的热应变，从而导致永久弯曲，而无需使用硬工具或外力。激光管弯曲的优点包括灵活性，特别是在多轴弯曲中，没有回弹，并且在外墙处壁没有变薄。然而，由于在每次激光扫描中产生的小弯曲，目前不实用激光管弯曲。具有矩形光束的高功率直接二极管激光器的出现提供了改善弯曲效率的潜力，但是需要解决一系列新的问题。本文基于有限元方法的热力耦合模型，对点弯曲，线源轴向加工，线源轴向不带水冷却和带水冷却的四种扫描方案进行了数值研究。并根据弯曲变形，输入能量，循环时间和变形管的特性进行了比较。还研究了重要参数（例如光束覆盖率，扫描速度和冷却偏移）对变形的影响。激光清洁是通过脉冲激光将表面污染物烧蚀去除而不会损坏基板表面的过程。由于其选择性，可控制性，环境友好性和灵活性，激光清洁是微电子清洁，艺术品修复和其他应用中的有前途的替代方法。研究了从微电子领域中使用最广泛的金属铜中去除氧化铜。氧化铜的化学分布和膜厚使用X射线光电子能谱和椭圆光度法进行表征。实验和数值研究了脉冲参数（例如激光强度，脉冲数和重复频率）对成功进行激光清洗的影响，其中使用二维轴向对称模型来更精确地模拟氧化铜的激光烧蚀清洗。石材艺术品，重要的是要保留石材的美学价值。清洁后石材（例如大理石）的变色阻碍了激光石材清洁的潜力。从热化学反应的角度提出了变色机理。硬壳中石墨对氧化铁的还原在确定清洁石材的表面颜色方面起关键作用。用包括反应热在内的激光烧蚀清洁模型分析热化学反应的动力学。还通过实验间接验证了热化学反应。对比研究了通量水平对使用355nm激光波长清洗后的大理石变色的影响。还通过实验和数值研究了薄液体层覆盖结壳的影响。提出了一个二维轴对称模型，以模拟考虑质量，动量和能量守恒的辐射结壳中温度，液体体积分数和蒸气压的变化。本文考虑了三种热力学性质不同的液体，即蒸馏水，乙醇和丙酮，以及它们对清洁大理石表面颜色的影响。大理石表面的化学成分通过表面增强拉曼光谱进行表征。表面色是使用1976 CIE L * a * b *颜色系统的色度计测量的。
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