# Deformation of Optics for Photon Monte Carlo Simulations

## TL;DR

This paper presents a comprehensive simulation approach for optical deformations in telescopes due to thermal and mechanical stresses, enhancing photon Monte Carlo simulations for astronomical imaging.

## Contribution

It introduces a coupled elasticity and thermal effects simulation method integrated into photon Monte Carlo optics modeling, validated and applied to real telescope data.

## Key findings

- Thermal effects cause second order PSF defocusing.
- Gravitational sag leads to structured PSF distortions.
- Thermal gradients produce elliptical PSF patterns.

## Abstract

We develop a comprehensive approach to simulate the deformation of mirrors and lenses due to thermal and mechanical stresses that couples efficiently to photon-based optics simulations. This expands upon previous work where we demonstrated a comprehensive ab initio approach to simulate astronomical images using a photon Monte Carlo method. We apply elasticity theory and estimate thermal effects by adapting a three-dimensional numerical method. We also consider the effect of active optics control systems and active cooling systems in further correcting distortions in the optics. We validate the approach by showing convergence to analytic estimates, and then apply the methodology to the WIYN 3.5m telescope primary mirror. We demonstrate that changes in the soak temperature result in second order point spread function (PSF) defocusing, the gravitational sag and positioning errors result in highly structured PSF distortions, and large-scale thermal gradients result in an elliptical PSF distortion patterns. All three aspects of the environment are larger than the intrinsic optical aberrations of the design, and further exploration with a variety of telescopes should lead to detailed PSF size and shape, astrometric distortion, and field variation predictions. The simulation capabilities developed in this work is publicly available with the Photon Simulation (PhoSim) package.