I understand fresnel lenses are manufactured using CNC machines. I was wondering, if it would be possible to use sound to vibrate liquid silicon and then fast cool it into the standard form of a fresnel lens? This occurred to me when I noticed that ripples on a pond resemble the lenses in question, and that certain frequencies can cause liquids to vibrate. So, hypothetically, could it be done, and if so, would it be faster than machining?
Probably not. A fresnel lens isn't just a rippled surface, it has discontinuities, or straight edges. The area of these edges mostly causes loss of incident power. The optics designer wants a good ratio of its (aspheric) area of use to its unused area at edges.
Sound and other vibrations could create sine wave-like ripples on the surface of a liquid, but never the discontinuous shapes required to make a fresnel lens. Interesting idea, though.