RII Track-4:NSF: Investigation of Stress Induced Birefringence and Refractive Index Changes in Glass for Fabricating Novel Optics

超快激光微加工技术能够可靠地改变材料特性，并在玻璃等材料中创造亚微米尺度的特征，具有高通量、高精度和低成本，可以用来促进各种光学器件的制造，包括波导、波片、体积光栅和量子光学。此外，它还可以生产用于天文反射镜、空间通信和虚拟现实设备的光学元件。超快激光微加工技术的许多应用依赖于实现折射率和/或双折射的可靠变化，以及向基底引入受控的应力状态。然而，由于激光照射既可以引发应力积累，也可以引发折射率的改变，两者之间的关系尚未得到很好的探索，导致不同程度双折射的潜在机制尚未完全了解，这限制了该技术在各种材料中的应用。在这个项目中，我们计划通过进行广泛的参数研究来研究不同超快激光加工条件下薄玻璃基板的应力诱导双折射和折射率变化来解决这一知识差距。从该项目中获得的知识将有助于提高激光写入光学元件的质量和提高衍射元件的效率。这项研究基础设施改善轨道4 EPSCoR研究人员项目将为新墨西哥大学的一名助理教授提供奖学金，并为一名研究生提供培训。该项目建议与亚利桑那大学（UA）的Brandon Chalifoux博士合作，他将提供最先进的飞秒激光材料加工系统（Trumpf TruMicro 2030）以及几个关键的计量工具。项目团队将利用该激光器在玻璃基板上定义明确的区域上书写，测量双折射、应力和折射率变化，并研究各种激光照射和聚焦参数，包括脉冲能量、脉冲持续时间、脉冲密度、偏振、光束整形和数值孔径。本项目的三个具体目标是：(1)利用配备微分干涉对比、相位成像和偏振相机的光学显微镜，开发测量双折射和折射率变化的程序；(2)利用超快激光加工参数组合，建立参数空间，在熔融石英和N-BK7玻璃中产生不同程度的双折射和折射率变化；(3)建立有限元模型，模拟激光加工区域的应力场和局部电场，并与实验测量结果进行比较。这项奖学金将对左恒博士的研究生涯轨迹产生变革性的影响。左恒博士是新墨西哥大学机械工程专业的一名早期教师，该大学是一所为少数族裔和西班牙裔服务的机构。它还将推进新墨西哥大学本科生和研究生的激光制造教育，提供实践研究培训机会，扩大代表性不足群体的研究参与，从而加强新墨西哥大学在先进制造领域的竞争力。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The capability of the ultrafast laser micromachining technique to reliably alter material properties and create sub-micron-scale features in materials, such as glass, with high throughput, high precision, and low cost, can be harnessed to facilitate the fabrication of various optics, including waveguides, waveplates, volume gratings, and quantum optics. Additionally, it enables the production of optical components that can be used in astronomy mirrors, space communication, and virtual reality devices. Many applications of the ultrafast laser micromachining technique depend on achieving a reliable change in refractive index and/or birefringence, as well as introducing controlled stress states to the substrates. However, since laser irradiation can trigger both the accumulation of stress and modification of refractive index, the relationship between them has not been well explored, and the underlying mechanism leading to different levels of birefringence is not fully understood, which limits the application of such techniques in various materials. In this project, we plan to address this knowledge gap by conducting an extensive parameter study to investigate stress-induced birefringence and refractive index changes in thin glass substrates subjected to different ultrafast laser processing conditions. The knowledge obtained from this project will contribute to improving the quality of laser-written optical components and enhancing the efficiency of diffractive elements.This Research Infrastructure Improvement Track-4 EPSCoR Research Fellows project will provide a fellowship to an Assistant professor and training for a graduate student at the University of New Mexico. This project proposes collaboration with Dr. Brandon Chalifoux at the University of Arizona (UA), who will provide access to a state-of-the-art femtosecond laser material processing system (Trumpf TruMicro 2030) as well as several key metrology tools. The project team will utilize this laser to write over a well-defined region on the glass substrate, measure birefringence, stress, and refractive index changes, and investigate various laser irradiation and focusing parameters, including pulse energy, pulse duration, pulse density, polarization, beam shaping, and numerical aperture. The three specific objectives to be pursued in this project are: (1) developing the procedure for measuring birefringence and refractive index change using an optical microscope equipped with differential interference contrast, phase imaging, and a polarization camera; (2) establishing a parameter space to create different levels of birefringence and refractive index changes in fused silica and N-BK7 glass using a combination of ultrafast laser processing parameters; and (3) developing a finite element model to simulate the stress field and local electric field in the laser-processed regions and comparing it with experimental measurements. This fellowship will have a transformative impact on the trajectory of the research career of the PI, Dr. Heng Zuo, an early-career faculty member in Mechanical Engineering at the University of New Mexico, a minority-serving institutionI and Hispanic-Serving Institution. It will also advance laser manufacturing education for undergraduate and graduate students at UNM, providing hands-on research training opportunities and broadening research participation among underrepresented groups, thereby strengthening UNM's competitiveness in the field of advanced manufacturing.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.