Laser ablation for thin mirrors
Dr. Heng Zuo, UMN
Title: Femtosecond laser micromachining for stress-based figure correction of thin mirrors
Speaker: Dr. Heng E. Zuo, Assistant Professor, University of New Mexico
Host: Antoine Wojdyla
Date and time: Friday, June 2, 2023 – 11am
Abstract: The fabrication of many high-resolution thin-shell mirrors for future space telescopes remains challenging, especially for revolutionary mission concepts like NASA’s Lynx X-ray Surveyor. It is generally harder to fabricate thin mirrors to the exact shape than thicker ones, and the coatings deposited onto mirror surfaces to increase the reflectivity typically have high intrinsic stress which deforms the mirrors further. Since the rapid development of femtosecond laser technologies over the last few decades have triggered wide applications in materials processing, we have developed a novel mirror figure correction and stress compensation method using a femtosecond laser micromachining technique for stress-based surface shaping of thin-shell x-ray optics. We employ a femtosecond laser to selectively remove regions of a stressed film that is grown onto the back surface of the mirror, to modify the stress states of the mirror.
In this talk, I will present experimental results to create both isotropic and anisotropic stress states on thin flat silicon mirrors with thermal oxide (SiO2) films using femtosecond lasers. We have shown that equibiaxial stress can be generated through uniformly micromachined holes, while non-equibiaxial stress arises from the ablation of equally spaced troughs. I will also present results from strength tests to show how this process minimally affects the strength of mirrors. These developments are beneficial to the high throughput correction of thin-shell mirrors for future space-based X-ray telescopes.
About the speaker: Dr. Zuo’s research interest lies at the junction of optics, mechanics, micro-/nano-engineering, computational modeling, and astronomy, with a focus on furthering the development and applications of high-performance space optical engineering systems. She is focused on designing and developing methods for fabricating and correcting space optical components, in combination with the implementation of advanced micromachining technologies such as femtosecond laser micromachining, assisted with finite element analysis and material testing. Her past research includes advancing technologies to aid in fabricating thin-shell high-resolution X-ray space telescope mirrors in the sub-half arcsecond HPD domain, including mirror figuring and correction technology, coating stress compensation techniques, and metrology development.
Dr. Zuo is joining the faculty of The University of New Mexico in August 2022. Before that, she was affiliated with MIT Kavli Institute for Astrophysics and Space Research, Research Laboratory of Electronics at MIT, MIT Microsystems Technology Laboratories, and MIT Materials Research Science and Engineering Centers. She has also been members of multiple professional societies including SPIE, OSA, APS, ASPE, AIAA, and SWE.