The stray-light entrance pupil concept and how it can be used to facilitate stray-light characterization

We introduce the concept of stray-light entrance pupil (SL-EP), which can be seen as the analogous regarding stray-light of the entrance pupil in optical design. It takes the shape of the rays footprint which by entering the system undergo stray-light effects before ultimately reaching the detector, modulated by the relative area importance. This paper discusses the properties of the SL-EP and the way it can be computed. The SL-EP can be used to improve stray-light simulations, as it allows to improve significantly the simulation accuracy while limiting the ray-tracing time. For that, sources can be defined based on the SL-EP and non-uniform ray densities can even be used to reach even higher performances. Time reduction factor up to more than 20 times can be demonstrated on the design of the 3MI earth observation instrument. Furthermore, the SL-EP concept can be used to facilitate experimental characterization of spatial point source transmittance maps.