多焦点激光诱导分离脆性透射材料机理及关键技术的研究

Large size crystal optical transmission materials, such as optical crystal, silicon rod, sapphire, quartz and glass, are difficult to cut materials. An innovation technology that multi focus laser induces a separation of transmission brittle materials is first proposed in this project. Based on the transmission material thickness and the crack growth mechanism, a multi focus derived optical system will be designed to make a focused laser beam form multi focus in material thickness direction. In this way, the temperature distribution uniformity along the material thickness direction can be improved, and the crack extension direction can be controlled to achieve safe high quality separation thick brittle transmission material. The KDP crystal is taken as an example in this project. The focused laser propagation and absorption characteristics as well as optical field distribution within and outside of the material in the multi focus derived optical system is study by mathematical simulation. The mathematical models of dynamic temperature field and thermal stress generated in the crystal are established to analyze the action of thermal stress and crack growth mechanism under conditions of multi focus and study systematically crack propagation mechanism and control technology. The design of the multi focus optical system is optimized by both cutting simulation analysis and experimental results. A new multi focus laser brittle transmission material cutting theory will be developed to solve the dilemma of the low product rate for large size optical crystal finished and the big waste for cutting brittle transmission material, and provide an effective way for non-destructive, highly efficient, rapid and high quality cutting separation of thick brittle transmitting material.

大尺寸晶体光学透射材料：如光学晶体、硅棒、蓝宝石、石英和玻璃等均属于难以切割材料。本项目首次提出多焦点激光诱导分离脆性透射材料的创新技术，根据透射材料厚度和裂纹生长机理设计出多焦点衍生光学系统，使聚焦激光束在材料厚度方向形成多个焦点，改善材料沿厚度方向温度分布均匀性，达到控制裂纹扩展方向，实现安全高质量分离厚脆性透射材料。本项目以KDP晶体为例，对聚焦激光在多焦点衍生光学系统中的材料传输吸收特性和材料内外的光场分布进行数学模拟研究；建立晶体中产生的动态温度场和热应力模型；分析多焦点作用下的热应力分布和裂纹生长机理；并对诱导裂纹扩展机制和控制技术进行系统的研究。结合切割模拟分析和实验结果对多焦点光学系统的设计进行优化，研发出一套全新的多焦点激光脆性透射材料切割理论，解决大尺寸光学晶体成品率低和脆性透射材料切割浪费大的困境，为厚脆性透射材料的无损、高效、快速高质量切割分离提供一条有效的途径。

大尺寸脆性透射材料，如光学晶体、玻璃、夹层玻璃等均属于难以切割的材料。其中KDP光学晶体是激光惯性约束核聚变装置所需的关键光学器件，但晶体胚件切割和超精密抛光加工的成功率和效率一直是阻碍我国“神光计划”项目的关键问题之一。而具备高透过率或反射率的玻璃常作为我国进口设备中高端超快激光器的谐振腔反射镜或高精密光学元件而备受关注以及夹层玻璃作为安全材料在航空航天、军事、建筑等方面具备广泛的应用，也存在切割分离效率低和质量差的问题而受限。因而本项目提出了具有自主知识产权的多焦点激光诱导分离脆性透射材料的创新技术，根据材料性质和裂纹生长机理研制出衍生多焦点激光光学系统和可调式多焦点激光光学系统，使聚焦激光束在材料厚度方向上形成多个焦点，进而改善材料沿厚度方向温度场和应力场分布的均匀性。通过研究多焦点激光在材料内部的光传输、吸收特性和动态温度、应力场分布模型，探讨了裂纹尖端微区热拉应力形成机理以及裂纹扩展原理，研发了相应的激光压束整形光学系统，掌握了裂纹尖端诱导裂纹扩展方向控制的关键技术，并对其过程进行数值模拟和实验优化研究，从而获得一套完整的多焦点激光诱导分离脆性透射材料加工理论技术。利用该理论技术实现了50mm厚KDP晶体抛光级无损快速切割分离，分离厚度至少为现有激光晶体分离的4倍，相应的分离速度可达200μm/s，约为传统机械分离技术的20余倍，分离表面粗糙度可达10.857nm，分离平整度达3.5389μm；实现了20mm厚钠钙玻璃的高质量切割分离，切割厚度为传统激光切割方法的2-4倍，切割表面粗糙度为1.6nm，达到镜面标准，切割速度为1mm/s。该项目共获得中国发明专利5项，实用新型专利7项，发表论文13篇（其中顶级SCI期刊5篇，SCI论文5篇，中文核心期刊3篇），并荣获一项国际荣誉，已超额完成本项目预期任务指标，由本团队在国内外首次提出的多焦点激光诱导分离脆性透射材料加工机理及关键技术具备极强的实际应用价值，对脆性透射材料的切割加工具有重要指导意义。