Opto-thermal analysis of a lightweighted mirror for solar telescope

TL;DR

This study uses 3D finite element analysis to investigate the thermal and mechanical behavior of lightweighted solar telescope mirrors, highlighting how temperature variations affect optical quality across different materials.

Contribution

It develops a realistic heat transfer model and evaluates thermo-elastic distortions and optical errors for three common mirror substrates using combined thermal, mechanical, and optical simulations.

Findings

Temperature distribution is non-uniform and affects mirror shape.

Thermo-elastic distortions contribute to optical figure errors.

Material choice influences thermal and optical performance.

Abstract

In this paper, an opto-thermal analysis of a moderately heated lightweighted solar telescope mirror is carried out using 3D finite element analysis (FEA). A physically realistic heat transfer model is developed to account for the radiative heating and energy exchange of the mirror with surroundings. The numerical simulations show the non-uniform temperature distribution and associated thermo-elastic distortions of the mirror blank clearly mimicking the underlying discrete geometry of the lightweighted substrate. The computed mechanical deformation data is analyzed with surface polynomials and the optical quality of the mirror is evaluated with the help of a ray-tracing software. The thermal print-through distortions are further shown to contribute to optical figure changes and mid-spatial frequency errors of the mirror surface. A comparative study presented for three commonly used substrate materials, namely, Zerodur, Pyrex and Silicon Carbide (SiC) is relevant to vast area of large optics requirements in ground and space applications.