The ASI is powered by QED’s powerful Subaperture Stitching Interferometry, and measures the surface of an optic by first evaluating smaller subsections, or subapertures, of the surfaces and then stitching together the results into a cohesive full-aperture map. Because the ASI considers only a smaller portion of the lens at a time, the fringes from mild aspheric departures can be resolved. However, with more severe aspheric departures, the fringe density of each subaperture is still too great.
The Variable Optical Null solves this problem; it is an advanced opto-mechanical subsystem that generates a wavefront that closely matches the surface of each aspheric subaperture being measured. This technique produces an interferogram with reduced fringe density compared to those produced using a normal spherical wavefront. In this way, significantly more aspheric departure within each subaperture can be tolerated, and larger and therefore fewer subaperture measurements are required. This process happens quickly – it typically takes between 15-30 seconds for each subaperture. A complex surface that required 20 subapertures could be measured in less than 10 minutes. It is also an automatic process; the ASI automatically selects and measures each subaperture without requiring user intervention. Once the subapertures are measured, the surface profile of the asphere is reconstructed using advanced stitching algorithms.
The outcome: fast, full-aperture, high-resolution measurements of aspheric surfaces.