Metrology for Freeform Optics (MFO)

Science requirements for optical instrumentation are requiring larger fields of view and faster f-numbers to complete their objectives.   Additionally, opportunities for CubeSat and SmallSat missions are growing as they are seen as a low-cost alternative to perform science for NASA.  These demands for fast, wide-field, and small-sized instrument payloads are challenging for traditional optical design forms due to the severe packaging constraints.  Optical surfaces with “freeform” shapes, however, enable additional degrees of freedom to help reduce volume and even eliminate surfaces from the more traditional design options.  Recent GFSC IRADs have investigated the capability of industry to manufacture these surfaces, but, as a final, capstone to this progress, funding is needed to improve the in-house metrology efforts to verify the components, and to develop new and better methods for assembly and alignment of this sensitive optical systems.  This work culminates the series of other GSFC IRAD work in the design and fabrication of freeform optics.  Furthermore, this effort is fully in line with improving GSFC’s capability for testing of other, more traditional aspheric surfaces to reduce costs and keep GSFC at the state of the art and competitive.

The objective of this proposed work is to mature the technology to reduce risk in implementing freeforms into optical systems and to improve metrology for aspheres in general.  This effort will focus on “metrology” of optical surfaces with freeform prescriptions. 

In this work, we will characterize existing optical components using CMM metrology and interferometry for both traditional and freeform optics.  We will explore and characterize sources of systematic and random error in the two metrology methods.  We will calibrate alignment fiducials using the CMM and then align a simple optical system with the fiducial-based approach, afterward verifying performance with interferometry.  A detailed comparison of methods and thorough characterization of uncertainties from these methods has hitherto not been performed to the nm-level needed for visible and UV missions.

This will improve GSFC’s capability to perform acceptance testing when vendors supply the Government with freeform optics.  This acceptance testing will consist of surface error checks using the CMM and fiducial calibration checks.  This will establish GSFC’s capability to align freeform optical systems using this fiducial-based approach.  This work will identify and document new technologies and pursue collaborations with industry through the New Opportunities Office, as appropriate.