飞秒激光构造铌酸锂表面平整微纳结构及其重掺杂机理研究

Currently for femtosecond laser-processed structures, especially induced periodic surface structures on Lithium Niobate crystal, are showing great application prospects in on-chip photonic-integrated and photoelectric (thermal) devices, and so on. However, there are still some challenges when using femtosecond laser to prepare periodic surface structures on Lithium Niobate crystal surface, and surface explosion is the most serious problem. In this project, by regulating the crystal surface carrier concentration and lattice relaxation process, we make use of femtosecond pulse laser irradiation to fabricate non-equilibrium heavy doped Lithium Niobate with micro-nano periodic surface structures. Methods such as pump-probe detection, transient emission spectroscopy and calculation of key parameter concerning laser-plasma interactions and phase transitions are employed to reveal the physical mechanisms of the nonlinear dynamic process of femtosecond laser interacting with Lithium Niobate crystal surface and the evolution of micro-nano structures on the surface. Established dynamic and thermodynamic model will not only illustrate the internal relations and interactions between doped elements, fabrication conditions, annealing methods and microscopic structural information of the material, but also help to demonstrate the internal mechanism of femtosecond laser induced heavy doping under extreme non-equilibrium conditions. Efforts will be made to explore the manipulating and the optimization of the macroscopic properties of heavy doped Lithium Niobate by femtosecond laser, which would provide both experimental support and theoretical evidence for the research of next generation micro-nano optoelectronic devices based on Lithium Niobate.

表面平整周期结构的铌酸锂晶体在单片光子集成与光电（热）器件等领域具有非常大的应用前景。针对当前飞秒激光加工透明晶体存在表面爆裂等技术难题，本项目提出在飞秒脉冲激光辐照铌酸锂晶体过程中，通过调控晶体表面载流子浓度和晶格驰豫过程，制备出具有平整周期性结构、且非平衡重掺杂的铌酸锂晶体材料。拟采用各种瞬态探测技术结合激光等离子体及相变过程中的关键参数，研究飞秒激光与铌酸锂晶体表面作用的非线性过程以及铌酸锂表面微纳结构演化的微观机理，建立超快脉冲激光构造微纳结构铌酸锂晶体的力学模型。建立掺杂元素、制备条件和退火方式与原子、电子等材料微观结构信息的内在关联和相互影响的规律，揭示极端非平衡条件下飞秒激光重掺杂的物理机制。力求从材料本质出发探索飞秒激光构造微纳结构重掺杂铌酸锂晶体的调控技术及其性能优化条件，为研制新型微纳结构的铌酸锂光电器件提供实验支持与理论依据。

以飞秒激光为代表的超快激光利用其作用速度超快、作用强度超强的特点，在材料增材、减材、改性领域有着广泛的应用。铌酸锂晶体作为一种关键的光电材料在许多领域都发挥着不可替代的作用。但受限于铌酸锂宽禁带、透明、硬脆的特点，其加工和改性问题都值得深入研究。.本工作旨在研究飞秒激光与铌酸锂晶体相互作用的理论、实验及相关应用。理论研究方面，本工作系统性地构建了飞秒激光与宽禁带透明材料相互作用的超快热力学模型、提出了全新的飞秒激光诱导深亚波长条纹形成机理。实验上，本工作首次实现了飞秒激光诱导铌酸锂表面大面积深亚波长条纹的加工、飞秒激光辐照重掺杂铌酸锂无裂纹微孔的加工。实际应用领域，本工作创新性地使用了基底加热辅助、表面镀膜辅助、脉冲整形辅助等多种手段调控飞秒激光与铌酸锂晶体的相互作用，提升了加工效率，优化了加工质量。.在项目的资助下，主要研究内容完成和深化如下：.A、飞秒激光构造铌酸锂、掺铁铌酸锂表面微纳结构及其物理机理研究。建立了一套基于双温模型改进的飞秒激光与铌酸锂相互作用的瞬态热力学模型，为后续工作给出了理论依据；搭建了一套飞秒激光变温加工系统，并依据理论进行了铌酸锂及掺铁铌酸锂晶体表面微纳结构的加工和调控，得到了大面积的表面周期性微纳结构；针对飞秒激光诱导表面深亚波长条纹的形成机理进行了研究，提出了全新的深亚波长条纹形成机理。.B、飞秒激光对铌酸锂的高精度加工及其机理分析。在实现了高温下无裂纹铌酸锂的加工的基础上，根据瞬态热力学模型等理论，系统分析了高温抑制飞秒激光加工铌酸锂缺陷形成的物理机理。.C、飞秒激光加工宽禁带透明材料的应用研究。针对实际应用，在高温辅助下飞秒激光可以实现铌酸锂的高效加工；在金属膜辅助下飞秒激光实现高效加工宽禁带透明材料；通过脉冲整形技术优化飞秒激光的色散，可以实现铌酸锂晶体重掺杂无缺陷加工。