A far Ultra-Violet Polarimeter by reflection for Pollux on board LUVOIR

The ultra-violet (UV) high-resolution spectropolarimeter Pollux is being studied in Europe under CNES leadership for the LUVOIR space mission. LUVOIR is a projected 15-m telescope equipped with a suite of instruments proposed to NASA. Pollux will perform spectropolarimetric measurements from 90 to 400 nm with a resolution of 120000. The spectrograph will be divided in three channels, each with its own polarimeter: far UV (FUV, 90-124.5 nm), mid UV (MUV, 118.5-195 nm), and near UV (NUV, 190-390 nm). We present here our FUV prototype and our investigation to optimize this polarimeter (angle, materials, coating...).