Online process diagnostics of ultrafast laser modifications and energy transport mechanisms in the volume of dielectrics and semiconductors

我们建议开发一种独特的在线工艺表征和优化设备，用于观察和分析透明和不透明介质和半导体内部的微观，超快激光诱导现象。提出的非破坏性方法将能够研究热积累，热和非热熔化，以及由此产生的质量传输和加工材料的形态变化。该表征设备将结合独特的定量检测瞬态折射率变化和诱导温度分布的能力，并具有亚皮秒的时间分辨率。实验获得的超快过程动力学知识将为激光与物质相互作用和随后的能量传递过程（如熔化和再凝固动力学）的基本描述提供重要数据。所提出的实验方法是利用超短脉冲白光连续发射和多线中红外辐射作为照明源，对加工材料进行光泵浦探针宽带干涉显微镜观察。这项研究将解决超快激光与物质相互作用过程的基本问题，以及随后在材料内部的能量转移，以及为许多其他具有非常广泛影响的技术问题提供解决方案。本论文的知识价值来自于对介质和半导体的超快激光辐照过程的理解。精确控制能量沉积到材料中的能力将能够研究亚稳聚集状态和近阈值激光材料加工的不同制度，热诱导应力和缺陷的研究，以及热积累效应。与之前在该领域的工作相比，基于可见光到中红外光谱探测范围内获得的实验数据，将首次实时测量光学相位变化和相关的热物理参数。这些关键的进步将使我们能够解决现有的和新的激光辅助制造技术的技术方面，例如光学玻璃中的波导写入，相似和不同材料的熔焊，以及电介质和半导体的批量选择性蚀刻。在线过程控制的工程挑战也将被解决。为了实现这些目标，将利用实时计算分析和基于反馈的过程优化技术。由于利用现有方法制造集成光子、电子和微流体器件严重依赖于重复性低的物理和化学过程，因此所提出的在线过程诊断和控制技术的广泛影响将是显著的。因此，对电介质和半导体的批量激光加工的过程理解和控制的增益将彻底改变当今光子学，电子学，传感和生命科学等微制造技术的广泛领域。特别是，医学芯片实验室应用的发展，如植入式诊断和治疗微型设备，将对我们的社会和医疗保健系统产生重大影响。与此提案相关的教育计划将涉及学生的参与，包括来自代表性不足的群体的学生，在光学，激光工程和材料科学的各个方面，并将研究成果纳入研究生和本科高年级课程。将开发相关的视觉学习和网络工具，以整合研究和教育活动。

We propose to develop a unique online process characterization and optimization facility for the observation and analysis of microscopic, ultrafast laser-induced phenomena deep inside transparent and opaque dielectrics and semiconductors. The proposed non-destructive approach will enable the study of heat accumulation, thermal and non-thermal melting, and resulting mass transport and morphology changes of the processed materials. This characterization facility will combine the unique ability to quantitatively detect transient refractive index changes and induced temperature distributions with sub-picosecond temporal resolution. The knowledge obtained experimentally of the ultrafast process dynamics will provide important data for the fundamental description of the laser-matter interaction and the subsequent energy transfer processes e.g. melting and resolidification dynamics. The proposed experimental approach is based on optical pump-probe broadband interference microscopy of the processed material utilizing ultra-short pulsed white-light continuum emission and multiline mid-IR radiation as illumination sources. This research will address fundamental aspects of ultrafast laser-matter interaction processes and the subsequent energy transfer within the material, as well as providing solutions to many other technological problems with a very broad impact. The intellectual merit follows from the process understanding during in-volume irradiation of dielectrics and semiconductors with ultrafast laser radiation. The ability to precisely control the energy deposition into the material will enable the study of metastable aggregation states and different regimes of the near threshold laser-materials processing, the study of thermally induced stresses and defects, as well as heat accumulation effects. Compared to previous work in the field, for the first time the optical phase change and associated thermo-physical parameters will be measured in real time, based on experimental data obtained in a spectral detection range from visible to mid-IR. These crucial advancements will allow us to address technological aspects of existing and novel laser-assisted fabrication techniques e.g. for waveguide writing in optical glasses, fusion welding of similar and dissimilar materials, and in-volume selective etching of dielectrics and semiconductors. The engineering challenges of the online process control will be addressed as well. In pursuit of these goals, real-time computational analysis and feedback-based process optimization techniques will be utilized. The broader impact of the proposed online process diagnostics and control technique will be significant since fabrication of integrated photonic, electronic and microfluidic devices with existing approaches relies heavily on physical and chemical processes having low reproducibilty. As a consequence the gain in process understanding and control for in-volume laser processing of dielectrics and semiconductors will revolutionize wide sectors of today’s micro-manufacturing technology in photonics, electronics, sensing and life sciences. In particular, the development of medical lab-on-chip applications e.g. implantable diagnostic and therapeutic micro-devices will significantly impact our society and healthcare system. The educational program associated with this proposal will involve student participation, including students from underrepresented groups, in various aspects of optics, laser engineering and materials science, and incorporation of the research results into graduate and upper-undergraduate courses. Pertinent visual-learning and web-based tools will be developed to integrate the research and education activities.