Thermal aberration of an off-axis mirror caused by temperature dropoff over its thickness

This paper presents a technique for calculating the thermal aberrations of off-axis mirrors used in earth-based telescopes where these aberrations are created by temperature dropoffs over the thickness of the mirror because part of the incident radiation is absorbed by the working surface. It is shown that there are general laws governing the formation of thermal aberrations in axial and off-axis optical systems. Under conditions of heat exchange, mirrors included in an earth-based telescope with a mounting design and an ambient medium that produce a temperature dropoff over the thickness of the mirror, the thermal aberration of the position of the focus for an off-axis mirror is identical to the thermal aberration that occurs under the same heat-exchange conditions in an axial mirror. The calculational technique developed here allows the requirements on allowable values of the absorbed radiation power to be made more precise and makes it possible to study how the thermal aberrations are affected by the defining parameters and to analyze possible ways to reduce the thermal aberrations. (C) 2017 Optical Society of America