What's it about?
The evolution from spherical, to aspheric, to freeform optics is quickly progressing towards more complex freeform surfaces. Freeform surfaces typically have little to no symmetry making the alignment of the surfaces difficult. The alignment of such freeform surfaces relative to the other features on the optic has been little considered. A typical alignment specification like wedge (edge thickness difference) is not well defined for freeform optics, nor is the wedge measurement. We show that by using fiducials during the manufacturing of freeform surfaces, the alignment and locating of the freeform surface can be specified and measured.
There is a large range of optical systems where freeforms are advantageous. Freeform optical systems can reduce the number of required components, thereby reducing weight, and dramatically improve system performance (reduced spot size) by reducing aberrations that cannot be corrected with rotationally symmetric optics. Howard and Wolbach1 showed the potential system improvement for a three-mirror telescope when freeforms (Zernikes) are added. The authors clearly indicate that free-forms are highly desirable. “It is clear …that freeform surfaces such as Zernike profiles have enormous potential for improving optical systems.”