Deterministic processing is critical to modern precision optics finishing. Put simply, determinism is the ability to predict an outcome before carrying out an activity. With the availability of computer numerically controlled (CNC) equipment & sophisticated software algorithms, it is now possible to grind & polish optics from a variety of materials to surface shape accuracies of 20 nm peak-to-valley (p-v), with surface roughness values (measured on white light interferometers over 250 µm×350 µm areas) to sub-nm root-mean-square (rms) levels. In the grinding phase the capability exists to estimate removal rates, surface roughness, & the depth of subsurface damage (SSD) for a previously unprocessed material, knowing its Young's modulus, hardness, & fracture toughness. An understanding of how chemistry aids in the abrasive-driven removal of material from the surface during polishing is also critical. Recent polishing process research reveals the importance of chemistry, specifically slurry pH, for preventing particle agglomeration in order to achieve smooth surface finishes with conventional pad or pitch laps. New sub-aperture polishing processes like magnetorheological finishing (MRF) can smooth & shape flat, spherical, aspheric & free-form surfaces within a few process iterations. Difficult to finish optical materials like soft polymer polymethyl methacrylate, microstructured polycrystalline zinc sulfide, & water soluble single-crystal potassium dihydrogen phosphate (KDP) can be finished with MRF. The key is the systematic alteration of MR fluid chemistry & mechanics (i.e. the abrasive) to match the unique physical properties of each workpiece.
