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

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.