Because the shape is formed by molecular forces rather than mechanical cutting, the resulting surfaces have a smoothness (roughness) of less than 1 nanometer, comparable to or better than the most expensive traditionally polished optics.
Instead of using physical molds or tools, researchers leverage the natural physics of liquids, specifically: Fabrication of complex optical elements from liquids
By submerging a polymer "liquid lens" into a second, density-matched liquid, the effects of gravity are neutralized. This allows surface tension to naturally shape the liquid into a perfectly smooth, mathematically precise curve. Because the shape is formed by molecular forces
A key feature of this fabrication method—often referred to as —is its ability to create high-quality optical components without mechanical processing (like grinding or polishing). Fabrication of complex optical elements from liquids