What is the rule-of-a-thumb ratio of lens' thickness to wavelength at which they can be designed using ray optics approximation? (The thickness is more relevant to gradient index lens, homogeneous lenses can be made arbitralily thin provided that you have a high enough refractive index material) Since lenses often have nontrivial shape, for simplicity sake let's consider a flat plate gradient index (otherwise it wouldn't be a lens) lens as shown on the picture. How many wavelengths thick at least should it be for the light to apparently take the path predicted by path integral?
closed as unclear what you're asking by sammy gerbil, Daniel Griscom, David White, rob♦ Jul 20 '18 at 20:56
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