Freeform optics have emerged as a new tool for optical designers and integrators. Manufacturing innovations are gradually increasing availability of precision freeform optics. As optics manufacturers strive to improve quality and decrease cost, some focus is placed on improvements in the challenging metrology requirements for freeforms. One relevant technique to be discussed here is the use of deflectometry to measure mid-spatial frequency error in-process or in-situ during the manufacturing of freeform parts. Deflectometry can measure the mid-spatial frequency error on freeform parts orders of magnitude faster than traditional tactile metrology tools at similar or better accuracy.

Freeform optics have become an important tool for the optical designer. These non-symmetrical optical surfaces have allowed unique solutions for complex optical designs. Optical manufacturers have continually improved the capabilities and precision of freeform optics to fill the need for these new optical designs. As new freeform manufacturing processes are developed so must the metrology to measure these optics. As with any complex process there is no single metrology tool for freeform optics. Some of the metrology tools for freeforms are the same as those used in traditional symmetrical optics; interferometry and profilometry. However, the uniqueness of freeforms presents more metrology challenges for manufacturing. One such challenge is the measurement of mid-spatial frequency (MSF) errors. The sub-aperture polishing process used to make freeform optics inherently induces artifacts onto the optical surface...

Read the Full Paper

This paper is posted on the SPIE Digital Library, clicking the button will direct you there.