StrayLux: an efficient tool for stray-light modelling in optical instruments

Stray-light components are an unavoidable part of the signal detected by most optical instrument; they can originate from different sources and optical design solutions can help reducing some of them. Diffuse stray-light results from the same scene observed by the instrument, and can deteriorate the radiometric performances especially in the presence of highlycontrasted scenes, as it often occurs in earth observation applications. When strict radiometric requirements are applied, as in the case of more recent mission studies, an assessment of stray-light levels can be relevant already in the early phases of an instrument development, to compare the performances of different concepts. For this task commercial stray-light tools using Monte-Carlo simulations can be extremely time consuming. Here we present the software StrayLux, a tool to calculate the diffuse stray-light component of optical instruments. This software uses a semi-analytical approach to approximate stray-light contribution of the optical components of an instrument, resulting in shorter calculation times than Monte-Carlo simulations. The tool is completely written in Python, is provided with a graphical interface, and can interact with Zemax to extract the relevant parameters of an optical design. The latest version of the software is currently made available to ESA industrial partners as a possible benchmark tool for stray-light estimation, within the instrument pre-development activities for future missions.