基于纳飞秒双脉冲激光的蓝宝石蚀除研究

Investigation on sapphire ablation by femtosecond-nanosecond dual beam laser

蓝宝石作为一种典型的宽带隙半导体材料具有良好的理化特性,在机械电子、航空航天、微电子等领域具有广阔的应用前景.本文提出采用纳飞秒双束激光进行蓝宝石加工的方法,利用飞秒脉冲峰值功率高的特性,通过多光子电离与碰撞电离,激发蓝宝石表面自由电子从而提高了蓝宝石对纳秒激光的吸收率,同时利用纳秒激光能量相对较大,技术成熟的优势,实现对蓝宝石材料的高质高效加工.为了揭示纳飞秒双束激光与蓝宝石材料的能量耦合机制,采用Fokker-Plank方程、Drude模型、双温模型对飞秒激光诱发的自由电子的演化过程及自由电子与入射激光之间的相互作用进行研究,并通过有限元仿真模拟了纳飞秒双激光与蓝宝石材料相互作用的能量耦合过程与蚀除过程,分析了纳飞秒双脉冲激光作用下,不同脉冲延时下等离子浓度的时空演化规律及其对入射激光吸收系数及反射率等表面光学特性的影响规律,揭示了纳飞秒双激光高效高质加工蓝宝石材料的机理.该研究对实现蓝宝石等宽带隙半导体等脆硬材料的高质高效加工具有重要意义.

Sapphire as a typical wide bandgap semiconductor material,has good physical and chemical properties and is widely used in mechanical electronics,aerospace,microelectronics and other fields.In order to improve ablation efficiency and at the same time ensure the processing quality,the ns-fs dual beam laser ablation method is proposed to process sapphire,which utilizes the high peak power of femtosecond pulses to excite free electrons through multiphoton ionization and collision ionization and the relatively larger fluence of nanosecond laser to improve the processing efficiency.In order to reveal the energy coupling mechanism between ns-fs dual beam laser and sapphire material,Fokker-Plank equation,Drude model and two-temperature model were used to study the evolution process of free electrons induced by femtosecond laser and the interaction between free electrons and incident laser.The energy coupling process and ablation process were simulated by finite element method,and the space-time evolution law of electron densities and its influence on surface optical properties such as absorption coefficient and reflectivity under different pulse delays were studied to reveal the mechanism of high-efficiency and high-quality processing of sapphire by ns-fs dual beam laser.This research is of great significance to the high-efficiency and high-quality processing of brittle and hard materials.