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USACM Large-Scale TTA Early-Career Colloquium (virtual)
Wednesday, October 04, 2023, 1:00 PM - 2:00 PM CDT
Category: Events

USACM Large-Scale TTA Early-Career Colloquium (virtual)

Understanding stress-based figure correction for ultrafast laser thin mirrors

Heng E. Zuo
University of New Mexico



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 Observatory. 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. On the other hand, rapid developments of ultrafast laser technologies in the past three decades have enabled high-accuracy high-throughput material processing and structuring with micrometer resolution. In this talk, I will discuss our efforts in figure correction and stress compensation of thin-shell mirrors by implementing ultrafast laser micromachining with stress-based figuring technique. We employ a 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. By using simple optical setups with a scanning X-Y stage, we have shown that both equibiaxial and general biaxial stress fields can be generated with laser micromachined features on thin flat silicon mirrors with silicon oxide films. We also built a finite element model to simulate the laser-induced stresses and resulting shape changes of thin mirrors due to the periodic patterning of a stressed film on silicon substrates using ultrafast laser ablation. We simulated the stress relief process in the thin-film/substrate system, and the numerical predictions compare reasonably well with curvature measurements for several different geometrical combinations of depth, width and spacing of the patterned troughs, achieving > 82% quantitative agreement with the experiments. I will also present strength testing analysis to show how this process minimally affects the strength of mirrors treated with ultrafast laser micromachining. These developments are beneficial to the high-throughput figure correction of thin-shell mirrors for space-based telescopes and other types of thin substrates used in the semiconductor industry.


Dr. Zuo is an Assistant Professor in the Department of Mechanical Engineering at the University of New Mexico since 2022. She received her PhD in Aeronautics and Astronautics from MIT in 2021, followed by a postdoc position at the MIT Kavli Institute for Astrophysics and Space Research. Before that, she obtained a M.S. in Aeronautics and Astronautics from MIT in 2017, and a B.S. in Engineering Mechanics from Tsinghua University in 2014. Her general research interest lies at the intersection of mechanical/aerospace/optical/material engineering, ultrafast laser micro/nanomachining, advanced manufacturing, computational modeling, and astronomy. 

Sponsored by USACM Technical Thrust Area on Large Scale Structural Systems and Optimal Design.
Contact for information about the seminar: [email protected].