At present, computer-controlled new optical polishing technology can use a wider range of substrate materials while enhancing the ability to polish free shapes.
The two main new base materials are aluminum and silicon carbide. Both materials offer advantages over traditional substrate materials such as glass and fused silica, especially in terms of increasing stiffness. In the past, the use of aluminum as a mirror substrate required the addition of a thick layer of nickel or other high reflective coatings. Now, with the new multi-step manufacturing technology, optical polishing can even be performed on low-cost aluminum alloys.
When Coherent used this technology, the substrate was first heat treated and then the single point diamond turning technology (SPDT) was used to machine the desired shape. However, the SPDT produces a groove texture on the parts that must be ground. To do this, the roughness is plotted using an interferometer or microscope, and then the "deterministic polishing" programming of the robotic system is performed using the acquired data.
The resulting high precision optical components surface shape using deterministic polishing techniques was λ/100 (633 nm), while the (root mean square) surface roughness was only a few angstroms.
Deterministic polishing techniques can also be used to machine non-spherical/cylindrical, so-called "free-form" optical components, whose optical complexity is much more complex than traditional symmetrical aspherical shapes. The use of free-form optics provides designers with powerful tools to reduce the number of system components and improve optical performance, reducing system weight, size and cost, and increasing resolution and field of view.
Advances in manufacturing technology have brought about dramatic changes in the market for aerospace optics. In the past, most custom aerospace optics were a single product. For example, a single optical component produced for special instruments such as the Hubble Space Telescope. But now, the global commercial aerospace industry (often referred to as the "new space") is increasingly using payloads, which are a distributed system of small satellites and therefore require multiple optical components. A copy. At the same time, a single large instrument is increasingly using a segmented primary BK7 glass optical mirror, and a single large optical component in the primary mirror is replaced by many small components. Deterministic polishing techniques are important in the development of these trends because they enable mass production of aspherical and free-form optical components with high repeatability and relatively low cost.
In summary, the market for aerospace optics has changed rapidly after relying on the same types of conventional optics for decades, due to the new manufacturing methods under computer control that led to the use of new materials and advanced polishing techniques.