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 highly-contrasted 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.