Active Optics Correction for the Thick Primary Mirror of the Lijiang 2.4 m Telescope Using Free-Vibration Modes
Year: 2025
Type: preprint
Abstract: Modern large telescopes rely on active optics for optimal image quality, but this technology is challenging to apply to thick mirror systems due to their high rigidity. The 2.4-m telescope at Lijiang Observatory has experienced significant image quality degradation, with the stellar full width at half maximum (FWHM) increasing from approximately 1 to over 2 arcseconds despite similar seeing conditions. This decline is attributed to high-order aberrations, including astigmatism, trefoil, and tetrafoil, which are uncorrectable by conventional focus adjustments. This study investigates, for the first time in China to our knowledge, the application of free-vibration-mode-based active correction—previously successful on thin-mirror telescopes—to a thick-mirror system. Using an 18-point active support system, we employed finite element modeling to evaluate the correction capabilities for various aberration modes. The simulations demonstrate high correction efficiency for astigmatism (>95%), along with significant correction for trefoil (84.47%) and tetrafoil (74.50%). However, the actuator forces required to correct trefoil, tetrafoil, and spherical aberration (31.33% efficiency) exceed practical limits. Therefore, the 18-point system is primarily effective for astigmatism correction. These results validate that free-vibration mode-based active optics offer a practical and effective solution for mitigating astigmatism in existing thick-mirror telescopes, thereby improving their observational performance.
Authors: peiliang que, baoli lun, liang xu, Yufeng Fan
Language: English
Subfield: Atomic and Molecular Physics, and Optics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
OpenAlex ID: W4413490602