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以高产量、高精度和低成本可靠地改变材料特性并在材料（诸如玻璃）中产生亚微米级特征的能力可以被利用来促进各种光学器件（包括波导、波片、体光栅和量子光学器件）的制造。此外，它还可以生产可用于天文镜、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，以及向衬底引入受控的应力状态。然而，由于激光照射可以触发应力的积累和折射率的修改，它们之间的关系还没有得到很好的探索，导致不同水平的双折射的潜在机制还没有完全理解，这限制了这种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解决这一知识缺口，以研究在不同的超快激光加工条件下薄玻璃基板中应力诱导的双折射和折射率变化。从这个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。这个研究基础设施改进轨道-4 EPSCoR研究员项目将为新墨西哥州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。该项目提议与亚利桑那大学（UA）的布兰登·查里富博士合作，后者将提供最先进的飞秒激光材料加工系统（Trumpf TruMicro 2030）以及几种关键的计量工具。该项目团队将利用该激光器在玻璃基板上的一个明确定义的区域上进行写入，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。本计画的三个具体目标为：（1）发展利用光学显微镜量测双折射及折射率变化的方法，此光学显微镜配备有微分干涉差、相位成像及偏光摄影机;（2）建立参数空间，以在熔融石英和N-BK 7玻璃中的应力场和局部电场;以及（3）开发有限元模型以模拟激光处理区域中的应力场和局部电场，并将其与实验测量进行比较。该奖学金将对PI的研究生涯轨迹产生变革性影响，Heng Zuo博士是新墨西哥州大学机械工程的早期职业教师，该大学是一所少数民族服务机构和西班牙裔服务机构。它还将推进UNM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，扩大代表性不足的群体的研究参与，从而加强UNM在先进制造领域的竞争力。该奖项反映了NSF的法定使命，并通过使用基金会的智力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.