Optical modeling for better on-orbit stray light background subtraction in the Roman Space Telescope Wide Field Instrument

The stray-light that a telescope receives from a contaminating source is described by the Normalized Detector Irradiance (NDI) function. NDI defines how much stray-light background will be seen at any point in the detector space from any (or every) source in the sky. NDI depends on the angular distance (R), position (roll, ϕ) angle of the source with respect of the detector axes and for especially wide field instruments like WFI, can vary widely as a function of position at the focal plane. Convolving the NDI with the position and flux of nearby stars directly provides a stray-light background correction. We present the optical model and ray trace results being used to generate a high-resolution NDI maps for the Nancy Grace Roman Wide Field Instrument, and describe the dominant scattering features associated with the structure seen in the NDI maps. These optical models are the core of ROSALIA (ROman Sky Analyst for Low surface brightness Imaging & Astronomy)