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I just want to know like in case of a prism what should the relation between angle of prism and its refractive index so the light ray continues to perform TIR in all its side and never gets out of it.

MUKUL
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1 Answers1

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Here's a theoretical possibility, though I don't think you could ever make it work in practice. Suppose your "prism" was doped with a fluorescent dye that would emit some wavelength, λ, when excited by a shorter wavelength of light. And, suppose that the prism and the dye were absolutely transparent at that wavelength.*

In that case, the excitation light could enter the prism where it would be absorbed by the dye molecules, and then those molecules would emit light of wavelength λ in all directions. Depending on the shape of the prism, some of those rays potentially would follow paths for which there was no exit from the prism. Every encounter with the surface would reflect the ray back into the body of the prism.

But, suppose you had trapped light inside the prism, and it really was bouncing around in there forever. How would you know? Maybe you could watch for a flash of light when you eventually break the thing. Otherwise,...?

* Of course, that's the impractical bit. You'll never find materials that are absolutely transparent. (See PM 2Ring's comments, above.)

Solomon Slow
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