COATING-INDUCED WAVE-FRONT ABERRATIONS - ON-AXIS ASTIGMATISM AND CHROMATIC ABERRATION IN ALL-REFLECTING SYSTEMS

The coatings used on telescope mirrors and other optical interfaces ca n have a marked effect on an optical system's image quality. We descri be the wave-front aberrations, particularly the defocus and on-axis as tigmatism, that are induced by the s- and p-phase shifts of coatings. These coating-induced wave-front aberrations are very small, particula rly near the design wavelengths of the coatings, but they can under ce rtain circumstances overshadow the geometric wave-front aberrations of the system. The wave-front aberrations that are induced by reflection -enhanced coatings on an f/1.5 Cassegrain telescope are numerically ev aluated as an example. A theory of coating-induced on-axis astigmatism and chromatic aberration is presented, and a simple algorithm that us es polarization ray tracing to calculate coating-induced defocus and a stigmatism coefficients in radially symmetric systems is provided.