An ultraviolet (UV) catadioptric imaging system, with broad spectrum correction
of primary and residual, longitudinal and lateral, chromatic aberrations for wavelengths
extending into the deep UV (as short as about 0.16 m), comprises a focusing
lens group with multiple lens elements that provide high levels of correction of
both image aberrations and chromatic variation of aberrations over a selected wavelength
band, a field lens group formed from lens elements with at least two different
refractive materials, such as silica and a fluoride glass, and a catadioptric group
including a concave reflective surface providing most of the focusing power of
the system and a thick lens providing primary color correction in combination with
the focusing lens group. The field lens group is located near the intermediate
image provided by the focusing lens group and functions to correct the residual
chromatic aberrations. The system is characterized by a high numerical aperture
(typ. greater than 0.7) and a large flat field (with a size on the order of 0.5
mm). The broad band color correction allows a wide range of possible UV imaging
applications at multiple wavelengths.