Imaging performance of telescope mirrors for far-ultraviolet astronomy

We describe image testing, surface metrology, and modeling of telescope mir rors (0.5 m in diameter, f/4.3) for the Far Ultraviolet Spectroscopic Explo rer (FUSE) satellite. Laboratory image testing of wavelengths in the visibl e, vacuum, and midultraviolet validated a theoretical analysis by use of th e Optical Surface Analysis Code (OSAC). Our modeling is based on surface me trology, including measurements of figure, midfrequency error, and microrou ghness. This combination of metrology, out-of-band performance testing, and modeling verified that the mirrors would meet mission requirements. We use OSAC to predict the FUSE telescope's far-ultraviolet (90-120-nm) point-spr ead function and assess its effect on instrument efficiency. The mirrors ha ve a 90% encircled energy diameter of 1.5 arc sec at lambda = 100 nm. Inclu ding the effects of spacecraft pointing error, the mirrors have a predicted average slit transmission at lambda = 100 nm of approximately 87% and 96% for the 1.25- and Q-arc sec-wide spectrograph slits, respectively, where th e required transmissions are 50% and 95%. (C) 2000 Optical Society of Ameri ca OCIS codes: 110.6770, 120.4800, 220.4840, 260.7210, 120.3940, 110.2960.