KDP晶体激光无损镜面加工机理及关键技术研究

项目名称： KDP晶体激光无损镜面加工机理及关键技术研究

项目编号： No.51475182

项目类型： 面上项目

立项/批准年度： 2015

项目学科： 机械、仪表工业

项目作者： 段军

作者单位： 华中科技大学

项目金额： 85万元

中文摘要： KDP晶体坯件的切割和超精密抛光加工一直是困扰我国完成ICF装置的关键问题之一。本项目首次提出KDP晶体激光无损镜面加工，将超快激光的冷加工效应和常规激光的热加工效应有机相结合，诱导微区应力线断裂原子或分子键，实现一次完成晶体分离和超精加工的一种创新技术。利用超快激光在KDP晶体近表层诱导相变、预制亚微米改性线和常规激光体吸收加热效应，在改性区形成纳米裂纹。通过研究裂缝和裂缝尖端的光传输、吸收特性和动态温度、应力场分布模型，探讨微区拉应力形成机理和应力断裂化学键理论以及微纳米裂纹扩展原理，得出一套完整的微区瞬间热应力断裂化学键理论。研发相应的激光压束整形光学系统，在切缝尖端形成特定的光场和温度场分布，诱导微纳裂纹的扩展，掌握其扩展方向控制的关键技术。对激光无损加工KDP晶体过程进行数值模拟，计算最优加工技术参数，同时进行实验优化研究，获得一套完整的KDP晶体无损镜面加工理论技术。

中文关键词： 激光加工；KDP晶体；无损镜面；机理；关键技术

英文摘要： Both cutting of KDP crystal blanks and ultra-precision polishing process of KDP crystal have been one of the key problems which plagued the completion ICF device in our country. The project of laser nondestructive mirror processing for KDP crystal is first proposed an innovative technology, which combines the cold effect of ultrafast laser processing with the hot effect of common laser processing to induce a micro stress line breakage atomic or molecular bonds so that both separation and super finishing of KDP crystal can be completed at the same time. The use of high peak power ultrafast laser pulses produces an nonlinear absorption effects with the occurrence of two-photon ionization or multiphoton ionization or impact ionization to prefabricate sub-micron laser induced phase transition line inside KDP crystal phase near surface.Then,a traditional main laser beam with higher transmittance, suitable energy and polarization direction is modified by a special optical system to obtain a suitable geometric dimension beam, which is adopted to scan the laser modified sub-micron line. Due to the absorption of the laser modified region is increased and the unmodified region remains relatively low, the difference in laser body absorption and thermal effects between the modified and unmodified region will produce a greater temperature gradient to form a specific internal stress and optical field distribution region.Since the modified region of atomic and molecular bond breaking or weakening, the thermal stress generated by the laser will break the bond along the atoms or molecules to form a nanometric crack. Further,a low power laser beam power at the front of the main laser beam alongthe laser modified line preheats the region to be processed in order to control and guide nano slit expansion trend. Meanwhile, the main laser beam produces a uniform heating along the thickness direction of slit side wall to separate and superfinish KDP crystal quickly due to heat expansion effect and atomic or molecular bond breakage. Some researches on the crack tip transmission, absorption characteristics,dynamic temperature and stress distribution model will be done to investigate the formation mechanism of micro tensile stress and stress rupture chemical bond theory as well as principles of micro-and nano crack, draw a complete micro-instant heat stress breaking chemical bond theory, master micro-and nano crack propagation direction control key technologies, research and develop corresponding laser beam shaping optical system to form a quasi-parallel laser line of focus characteristics. The researches of simulating laser nondestructive mirror finishing the best technical parameters and experiment optimization will be also carried out to achieve a new technology theory of effective laser nondestructive mirror processing to complete instant KDP crystal superfinishing nondestructive mirror separation processing.

英文关键词： Laser processing;KDP crystal;Nondestructive mirror surface;Mechanism;Key technologies