Abstract

The family of Three Mirror Anastigmats, (TMA’s), has been around for many years. Various design forms have surfaced over the years spanning focal, afocal, relayed and direct imaging telescopes. Two common design forms are shown in Figure 1. For missile optics, (optics in a tube), it is important to use a reimaging design with a buried cold stop near the detector for stray light suppression. Many times this is done with a Cassegrain type front end and a refractive relay group to relay the intermediate image to the detector. TMA’s offer the following optical advantages over the refractive relay configuration. TMA’s allow the correction of three basic aberrations, (spherical, coma and astigmatism), hence, a larger field of view. The sum of the mirror powers can be zero, yielding a flat field and hence a larger field of view on a flat focal plane array, (FPA). The TMA can be relayed, (also termed reimaged), and thus provide good stray light suppression for out-of-field radiation. Relaying a Cassegrain with a refractive assembly compromises the spectral coverage, introduces thermal defocus issues, has the wrong field curvature, is less radiation hard, and lowers transmission relative to a TMA. The TMA proposed here is achromatic and can be used over any spectral band. If made of one material, it may be passively athermal.

© 1998 Optical Society of America