Dimensional metrology of optics and production datums for a three-mirror freeform telescope

Freeform optics introduce new degrees of freedom that allow designers to decrease a telescope’s volume and/or enhance its imaging performance. Because freeform elements must be positioned accurately in six degrees of freedom, and must be fabricated using novel processes, optomechanical design for freeform systems presents new production challenges compared to traditional optical systems. New metrology techniques and platforms must be developed to evaluate form errors and misalignments in these freeform optics, including misalignments between datum sets used during different production processes. This work begins an investigation into the alignment fidelity and form accuracy in the diamondmachined freeform optics of a reflective triplet telescope and investigates the degree to which these errors affect the system’s image quality. The imaging performance of this telescope is evaluated by testing both its modulation transfer function and wavefront error, and connections are drawn to the preliminary results of the mirrors’ form metrology. A chromatic confocal surface profiler is used to measure the telescope’s three freeform mirrors, including the optical prescription as well as assembly and fabrication datums.