深紫外准分子激光辐照固体透明介质激发光致损伤的物理机制及应用研究

The ability to fabricate micro and nano-structures is crucial for the development of new materials and multifunctional micro-systems and devices. By focusing laser pulses inside the bulk of transparent materials high intensities can be achieved, which initiate nonlinear processes leading to important modifications of the structure of the materials. The induced permanent structural changes in the samples, such as the selective change of the refractive index, can be used for the fabrication of photonic structures and three-dimensional integrated optical devices inside optical materials.The fabrication and performance of photonic devices in transparent medium depend on laser-induced damage mechanism and controll of modulation depth. Howerever, mechanism and application of laser-induced damages in transparent solids focusing by deep ultravoilet (DUV) excimer lasers characterized with high photonic energy are reported less.In order to develop a photonic devices fabracation method in transparent solids induced by excimer lasers, understand the mechanisms of the laser-induced damages irradiated by DUV lasers pulses, and invesgate contrlling methods of laser-induced damages modulation depth,the project is proposed. Furthermore, based on filamentation branching in transparent mediums by astigmatically focused laser pulses, fabracate and characterize Y-type waveguides in transparent solids.

微纳结构光学器件的加工能力对新材料和多功能微系统与微器件制造至关重要。通过强激光脉冲作用于固体透明介质，利用非线性光学作用在材料内部调制材料结构能够实现这一目标。样品中产生的永久性结构改变，例如选择性折射率变，能够用于在光学材料内部制造光子结构和三维集成光学器件。基于透明介质的光子器件的制备和性能很大程度上取决于光致损伤的机制与其调制深度的控制。目前，基于拥有较高光子能量的纳秒级深紫外准分子激光激发固体透明介质的光致损伤及其应用仍有待研究。本项目旨在发展一种基于准分子激光聚焦固体透明介质激发光致损伤的方法制备光子器件，分析深紫外激光激发固体介质光致损伤的物理机制，解决光致损伤调制深度的控制途径等关键技术问题。在此基础上，结合像散聚焦透明介质产生光丝分叉的原理，在透明固体材料内部制备Y型波导，对其进行原理验证和初步表征。

系统研究了深紫外激光聚焦熔融石英产生的光丝及其激发的光致损伤，对损伤通道的结构和形貌进行了显微成像和表征。显微结果表明激光脉冲能量高于介质自聚焦阈值后可激发光丝现象，光丝与介质的热效应激发了光丝轨迹相关的损伤通道。.研究发现通过调节脉冲能量和辐照脉冲数量、聚焦物镜的焦距和工作距离等途径可实现对光丝和损伤的控制，解决了光致损伤调制深度的控制途径等关键技术问题。结果表明高脉冲能量的激光光束所激发的光丝和损伤通道更长，直径更大；损伤通道的长度随着聚焦脉冲数量的增加而增加，光学损伤在聚焦脉冲辐照的初期沿着光轴逆向生长迅速，并随着脉冲数量的增加区域饱和，损伤最终长度与脉冲能量密切相关；聚焦物镜的焦距更长，相应的损伤通道的直径更长；焦点由材料内部移到材料入射面之前，材料内部的光丝和损伤长度基本稳定，而焦点在材料表面和外部时激发的光丝和损伤锐减。.结合吸收光谱和激光感生荧光光谱，分析纳秒级深紫外激光聚焦熔融石英激发光致损伤的物理机制。损伤区域的LIF峰强度明显比原始材料的荧光峰信号强，说明损伤区域由光丝过程激发了光致缺陷，较强的荧光峰信号是光致缺陷激发的光学吸收的结果，结果表明介质内的光丝激发了材料内部永久性的光学损伤。.最后，初步探讨了熔融石英光致损伤的修复技术途径，实验发现在损伤通道的尾部，持续辐照损伤生长饱和的通道尾部，发现热效应产生的再熔融过程对损伤区域的材料均匀性有明显改善，为进一步研究损伤的修复技术提供了思路。