Characterization of pinholes on polyimide-based filters for NewAthena

To protect its sensors and ensure optimal working conditions, the NewAthena space mission will employ optical blocking filters; any defect on these filters, such as the presence of pinholes, could undermine the mission performances. One of the possible technologies for these filters consists in polyimide pellicles coated with a thin aluminum coating. This work presents the characterization of pinholes for some Al-coated polyimide pellicles using digital optical microscopy and image analysis algorithms, to compare the presence of pinholes with the transmittance performances of the filters in the medium infrared, ultimately showing how this approach can be used to evaluate the impact of pinholes on filters performances and the effect that different thicknesses of metal coatings can have on the pinhole formation.