Catadioptric illumination system for metrology

摘要

A catadioptric optical system (1200) operates in a wide spectral range. In an embodiment, the catadioptric optical system (1200) includes a first reflective surface (57) positioned and configured to reflect radiation; a second reflective surface (58) positioned and configured to reflect radiation reflected from the first reflective surface as a collimated beam, the second reflective surface having an aperture to allow transmission of radiation through the second reflective surface; and a channel structure (1380) extending from the aperture toward the first reflective surface and having an outlet (1330), between the first reflective surface and the second reflective surface, to supply radiation to the first reflective surface.