Compensation for general asymmetric static loads for a complete optical system of freeform mirrors.

Abstract

Optical systems consisting of freeform metal mirrors are state of the art in optical engineering. The freeform shapes allow for more compact designs and offer more degrees of freedom for aberration correction. The metal components allow for the relocation of the effort from the integration to the fabrication stage. Metal mirrors for spaceborne optical systems experience several loads during orbital commissioning or operation. The present paper focuses on describing general static loads within the optical design to close the iteration loop between optical and mechanical design using this knowledge to investigate how to compensate for load-induced surface shape errors within the optical design. First, this analysis is performed for a two-mirror system with an asymmetric force load step. Second, the compensation for this load is discussed by performing another optical design step or a direct mechanical compensation step at mechanical design level. Since thermal loads usually introduce expansion effects, a third point of the paper is the discussion of thermal loads with some general results, to embed them into the shown formalism. The paper concludes by showing residual optical errors of the compensated optical system and comparing them with the nominal design.