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使研究热积累，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成为可能。这种表征设备将结合独特的能力，以亚皮秒的时间分辨率定量检测瞬时折射率变化和诱导的温度分布。实验上获得的超快过程动力学知识将为激光-物质相互作用和随后的能量传递过程(如熔化和再结晶动力学)的基本描述提供重要数据。该实验方法以超短脉冲白光连续辐射和多线中红外辐射为照明源，基于光学泵浦-探测宽带干涉显微镜对被加工材料进行实验研究。这项研究将解决超快激光-物质相互作用过程的基本方面以及随后材料内的能量转移，并为许多具有非常广泛影响的其他技术问题提供解决方案。智能的优点来自于对超快激光辐射电介质和半导体的体积辐照过程的理解。精确控制能量沉积到材料中的能力将有助于研究亚稳态聚集态和近阈值激光材料加工的不同区域，研究热致应力和缺陷，以及热积累效应。与以前的现场工作相比，将首次根据在可见光到中红外光谱探测范围内获得的实验数据，实时测量光学相变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，例如在光学玻璃中写入波导、相似和不同材料的熔化焊接以及介质和半导体的体积选择性蚀刻。还将解决在线过程控制的工程挑战。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。拟议的在线工艺诊断和控制技术的更广泛影响将是显著的，因为利用现有方法制造集成的光子、电子和微流控器件在很大程度上依赖于重复性较低的物理和化学工艺。因此，对电介质和半导体的批量激光加工的工艺理解和控制方面的进展将彻底改变当今光电子、电子、传感和生命科学中的微制造技术的广泛领域。特别是，芯片上医学实验室应用的发展，例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。与这项提议相关的教育计划将涉及学生参与，包括来自代表人数不足的群体的学生，学习光学、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高等本科课程。将开发相关的视觉学习和基于网络的工具，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.