Simulations of stray light from the surface scattering of the Solar Corona Imager primary mirror

TL;DR

This paper models and analyzes stray light caused by surface scattering of the primary mirror in the Solar Corona Imager, proposing methods to suppress it and recommending the K-correlation model for simulation.

Contribution

It introduces three scattering models in Zemax to evaluate stray light and provides optimized parameters for suppression, highlighting manufacturing limitations.

Findings

Stray light decreases with field of view in both channels.

Stray light in Ly-alpha is lower than coronal emission, but higher in white-light.

K-correlation model is recommended for surface scattering simulation.

Abstract

The Solar Corona Imager is an internally occulted coronagraph on board the ASO-S mission, which has the advantage of imaging the inner corona in H I {Lyman-\textalpha} (Ly-alpha) and white-light (WL) wavebands. However, scattering of solar disk light by the primary mirror (M1) becomes the main source of stray light. To study the methods of stray light suppression, three scattering models are used to model M1 scattering in Zemax OpticStudio. The ratio of coronal emission to predicted stray light decrease along field of view in both channels. The stray light in Ly-alpha channel is generally lower than coronal emission, but the stray light in WL channel tends to be one order of magnitude higher than coronal signal at 2.5 Rsun. Optimized parameter combinations that suppress the stray light to required level are obtained, which put some limitations on the M1 manufacture. Besides, K-correlation model is recommended to simulate surface scattering.