飞秒激光微加工质量优化的若干问题研究

发布时间：2018-05-24 05:30

本文选题：飞秒激光 + 微加工　；参考：《上海大学》2017年博士论文

【摘要】：飞秒激光是一种超短脉冲激光,可以在单脉冲能量很低的条件下获得GW甚至TW量级的瞬时功率,这使得飞秒激光与物质作用时表现出显著的非线性现象。近年来,运用双光子诱发光敏材料发生光聚合反应实现三维微加工已经成为微纳加工领域的研究热点,并逐渐发展成为一种集超快激光技术、光化学材料技术、显微技术、超高精度定位技术、CAD/CAM技术于一体的新型微纳米加工技术。飞秒激光双光子微加工一般采用直写方式,按照预定轨迹在聚合物材料内部逐点扫描。对于给定的加工系统和被加工材料,空气和被加工材料折射率不同产生的像差、加工点光斑的椭球形分布、扫描步距的大小等因素是影响加工精度和表面质量的重要因素。本文在像差补偿、光斑三维整形技术以及扫描步距的优化方法等方面开展了一些探索性的工作,主要内容如下:1.对飞秒激光微加工实验系统的曝光控制系统进行了机械和电气改造,扩展了三维扫描平台的运动范围,实现了加工对象的多样化和多轴联动下的空间三维连续扫描。2.根据飞秒激光微加工机理,结合光在不同介质中的传播理论,分析了由于空气和被加工材料折射率的不同对加工点光斑的光强分布产生的影响,并进行了数值模拟。利用波前像差函数推导出了由于折射率不同引起的像差表达式,得出了随着加工深度、物镜数值孔径、加工介质折射率的增大,像差也随之增大的结论。在此基础上,建立了基于反向泽尔尼克多项式的像差补偿模型,以飞秒脉冲激光在光致变色材料上进行点加工为例对该补偿模型进行了数值模拟。仿真结果表明建立的补偿模型能有效校正像差。初级像差补偿后,加工点荧光信号强度衰减现象得到显著改善,加工深度可接近600μm;二级像差补偿后,信号强度基本不随加工深度的改变而改变。提出了基于开普勒望远镜系统的像差补偿方法并进行了实验验证,分析了补偿效果。3.基于菲涅耳衍射理论,结合飞秒激光微加工焦点光斑横向和轴向的归一化光强分布函数,对加工点光斑形状进行了数值模拟。在分别对光斑轴向和横向整形技术的理论分析和数值模拟的基础上,得到了基于光通滤波器的光斑三维整形效果的表征参数,运用全局优化算法与遗传算法对光束整形元件(相位板)的关键参数进行了优化设计。根据优化设计和数值模拟的结果制作了四环复透过率相位板并进行了验证实验。实验结果表明,加入相位板对激光束进行三维整形后,加工点横向和轴向尺寸明显变小,光斑压缩比例与理论计算结果基本吻合。介绍了通过狭缝光阑、增加柱透镜组和增加预聚焦透镜等三种改善加工点光斑非对称性形状的光束整形技术,对其工作原理及实现方法进行了详细的分析。4.基于光强分布函数和自由基浓度理论,建立了飞秒激光微加工固化单元覆盖率的数学模型,分析了覆盖率大小对微器件表面质量和加工效率所造成的影响。运用曝光等效性原理,得到了微器件表面质量特征参数与扫描步距之间的表达式,并进行了数值模拟和实验。结果表明当扫描步距远小于固化单元尺寸时,其对线条表面质量的影响较小,而当扫描步距逐渐增大,线条表面的平滑性迅速降低,表面质量急剧变差。针对具有不同斜率的立体器件加工,提出了连续可变间距的三维扫描方法,推导出了不同斜率处扫描步距的计算表达式。以球形结构的加工为例进行了对比实验。结果表明,相对于固定步距扫描法,采用连续变步距扫描法进行微加工,能够有效地改善微器件的表面质量。
[Abstract]:Femtosecond laser is an ultra short pulse laser, which can obtain instantaneous power of GW or even TW at the low energy of single pulse. This makes the femtosecond laser and substance play a significant nonlinear phenomenon. In recent years, the application of photopolymerization with two-photon induced photosensitive materials to achieve three-dimensional micromachining has become a micro Naga. The research hotspots in the field of industry have gradually developed into a new micro nano processing technology, which integrates ultra fast laser technology, photochemical material technology, micro technology, ultra high precision positioning technology and CAD/CAM technology. The femtosecond laser two-photon micro machining generally uses direct writing method, and it is scanned in the polymer material point by point according to the predetermined trajectory. For the given processing system and the processed material, the aberration produced by the refractive index of the air and the processed material, the ellipsoid distribution of the spot spot of the machining point, the size of the scanning distance are the important factors that affect the machining precision and the surface quality. The main contents are as follows: 1. the mechanical and electrical transformation of the exposure control system of the femtosecond laser micromachining experiment system is carried out, the motion range of the 3D scanning platform is extended, and the spatial 3D continuous scanning.2. under the diversity of the processing objects and the multi axis linkage is realized according to the femtosecond laser micro addition. Combined with the propagation theory of light in different media, the influence of the difference of refractive index of air and the processed material on the intensity distribution of the light spot of the processing point is analyzed, and the numerical simulation is carried out. The aberration expression caused by the difference of the refractive index is derived by the wavefront aberration function. The numerical aperture of the mirror increases the refractive index of the medium and the aberration increases. On this basis, the aberration compensation model based on the reverse Zelnick polynomial is established. The compensation model is simulated with the femtosecond pulse laser processing on the photochromic material as an example. The simulation results show the compensation of the compensation model. The model can effectively correct the aberration. After the primary aberration compensation, the intensity attenuation of the fluorescent signal of the processing point is greatly improved, the processing depth can be close to 600 m. The signal intensity is basically not changed with the change of the processing depth after two stage aberration compensation. Based on the theory of Fresnel diffraction,.3. based on the theory of Fresnel diffraction and the normalized light intensity distribution function of the femtosecond laser micromachining focal spot in the transverse and axial direction, the shape of the spot light spot is simulated. Based on the theoretical analysis and numerical simulation of the axial and transverse shaping techniques of the spot, the optical filter is obtained. The key parameters of the beam shaping element (phase plate) are optimized by the global optimization algorithm and genetic algorithm. The four ring complex transmittance phase plate is made according to the optimization design and the numerical simulation results. The experimental results show that the phase plate is excited by the addition of the phase plate. After the three-dimensional shaping of the beam, the transverse and axial dimensions of the processing point are obviously smaller. The compression ratio of the spot is basically consistent with the theoretical calculation. Three kinds of optical beam shaping technology are introduced, which are through the slit aperture, adding the column lens group and increasing the prefocus lens to improve the asymmetrical shape of the spot spot. The working principle and the realization method are also introduced. A detailed analysis of.4. based on the light intensity distribution function and the free radical concentration theory is used to establish the mathematical model of the coverage rate of the solidification unit of the femtosecond laser micromachining. The influence of the coverage rate on the surface quality and the processing efficiency of the microdevices is analyzed. The surface quality characteristic parameters and scanning of the microdevices are obtained by using the exposure equivalence principle. The results show that when the scanning step is far less than the size of the curing unit, it has little effect on the surface quality of the line, and the smoothness of the line surface is rapidly reduced and the surface quality is badly changed when the scanning step is gradually increased. A three-dimensional scanning method with continuous variable spacing is proposed, and the calculation expression of the scanning step at different slopes is derived. A comparison experiment is carried out with the machining of the spherical structure as an example. The results show that the continuous step distance scanning method can effectively improve the surface quality of the microdevices with the continuous step distance scanning method.
【学位授予单位】：上海大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TG665

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