Theoretical and measured encircled energy and wide-angle scatter of SUMER demonstration telescope mirror in FUV

摘要

Abstract: The theoretical encircled energy and wide angle scatter of the SUMER Demonstration Telescope (SDT) mirror was analyzed at the wavelength of 123.6 nm. The modeling was accomplished with two software packages: (1) Metrology Data Processor (METDAT) and (2) Optical Surface Analysis Code (OSAC). The modeling is based on measured mirror surface figure error data and roughness characteristics covering all important spatial frequencies affecting the imaging in the Far Ultraviolet (FUV) wavelength region. The performance of the SDT mirror including the encircled energy and wide angle scatter was also directly measured at 123.6 nm. We found an excellent agreement between the measured and theoretical encircled energy up to about 3 arcseconds from the peak and wide angle scatter up to about 20 arcminutes from the peak at 123.6 nm. The 80 percent encircled energy diameter of the SDT mirror is about 2.6 arcseconds and the amount of scattered light drops to about 5.0 $MUL 10$+$MIN@10$/ of peak irradiance 20 arcminutes from the peak. The performance of the mirror in the FUV is degraded by the mid-frequency errors.!13