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I want to delay visible light (~450nm-600nm) by 10ns. One way would just be to have it travel about 10ft since the speed of light is about 1ft/ns. Could I reduce that length by sending it through some high index of refraction material? Dispersion is a bit of a concern in that case I guess. Any recommendations for what that material should be?

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This may not be a complete solution, but you can use mirrors! It's not hard to design a mirror-based optical system which will have the property you are looking for. This reminds me of an interesting Project-Euler question.

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Or a less fancy but more practical way would be to use two simple planar mirrors, carefully aligned.

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  • $\begingroup$ I agree with using mirrors. A more practical system is to use just two ordinary planar mirrors, that are parallel (or almost-parallel) to each other. The light can bounce back and forth 10 times no problem, and it's easy to align and set up. $\endgroup$ – Steve Byrnes Jul 4 '13 at 19:11
  • $\begingroup$ @SteveB Indeed, I should add that to my answer! $\endgroup$ – Ali Jul 4 '13 at 19:13
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I don't know if the following would suit you, but you can run light through a coiled optical fiber.

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  • $\begingroup$ @Jim: This is not obvious to me. Care to explain? $\endgroup$ – akhmeteli Jul 5 '13 at 1:01
  • $\begingroup$ This is in fact exactly analogous to the way nuclear and particle physics signals are delayed for in some cases and was exactly the answer that occurred to be for signals that are point-like in origin (i.e. not images) or will tolerate being pixelated at the input head of a bundle of fibers. The speed of light in typical fibers is around $2/3\,c$. $\endgroup$ – dmckee --- ex-moderator kitten Jul 5 '13 at 3:25
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Wikipedia's list of refractive indices doesn't list any above 4, and I doubt you want to pass your light through 2.5 feet of something. You're probably better off just having the light bounce back and forth between some mirrors or passing it through a coiled optical fiber (like Ali and akhmeteli suggested.

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