Telescope Stray Light – Fundamental Optical Plumbing & Early Experience with SOFIA

Effective stray light control is a key requirement for wide dynamic range performance of scientific optical systems, particularly in the infrared. Unwanted radiation can deteriorate detection measurement by contributing high background flux/noise as well as stochastic (such as telescope pointing dependent) variations that degrade instrument calibration performance. Designs for stray light control solutions cover a wide range of technologies and approaches: baffles and structures, specialized low and high emissivity coatings and coatings maintenance. The talk will discuss a number of stray light control aspects employed for two 2.5 m class telescopes: SDSS and SOFIA. Thus far, the experience from several hundred SOFIA missions have revealed that the completed telescope and environmental conditions are well matched to provide good stray light performance for many years of science missions; far fewer mirror re-coatings are now anticipated. At low flux levels, platform aircraft engine glow has presented a challenge for some observations; this will be discussed was well as solutions which have been developed, some successfully implemented.