Visible light transmittance of micro-pore optic plates for the wide-field x-ray telescope on the Einstein probe

Micro-pore optics (MPO) has been employed in space x-ray telescopes for large field-of-view observations. For x-ray focal plane detectors with visible photon sensing capability, the optical blocking filter (OBF) on MPO devices is critical for preventing signal contamination by those photons. In this work, we designed a piece of equipment to measure the light transmission with high accuracy. The transmittance test results of the MPO plates meet the design requirements of less than 5×10^-4. Based on the multilayer homogeneous film matrix method, we estimated possible combinations of film thicknesses (with alumina) that show a good agreement with the OBF design.