Freeform TMA without planar symmetry for compact catoptric imaging system

Abstract

In this article, the impact of the suppression of planar symmetry in three mirror reflective designs is studied through the example of a reference TMA optimized to be diffraction limited in the near infrared (NIR) spectrum. This reference TMA has a symmetry over the YZ plane, and a bounded volume of one cubic decimeter (volume of 1U cubesat) with the parabasal ray being normal to one side of the cube. A second TMA is then derived from this reference with no planar symmetry. This second TMA is still diffraction limited in the NIR spectrum while having a 11% longer focal length for the same maximal volume. A study of manufacturing complexity of the surfaces show no added complexity of the surface other than the removal of any symmetry. Parameters such as freeform sag and orthoradial slopes are compared suggesting that surfaces of the asymmetric system are simpler to manufacture.

Keywords

• Freeform
• Optical Design
• Three mirror imager
• Cubesat