We know light rays incident on a surface face three types of events.

  1. proportion of it is absorbed
  2. some of it is reflected &
  3. remaining part of it gets refracted.

In case of Total Internal Reflection, we know, not only does normal reflection occur (2), but also its refractive part (2) get reflected.

What happens to the (1) part? Is it also reflected or just get absorbed by the surface? If part (1) is absorbed like all other cases, why do we call it 'total'?

  • $\begingroup$ Surfaces are thin, do not really absorb any substantial amount. $\endgroup$ – Pieter Apr 11 '18 at 22:03

The word "total" in "total internal reflection" is used in the following sense: all of the light that could possibly propagate away from this surface is reflected, and none is refracted. The absorbed portion is still absorbed, as usual, but since it doesn't propagate away from the surface, it's still consistent with our usage of "total" above.

As a side note, though total internal reflection means that no light will refract through the surface, that doesn't mean that there is no electromagnetic field on the other side of the surface. In reality, beyond the surface, there exist exponentially-decaying evanescent waves which do not propagate or carry energy away from the surface, but can still be detected and used to, for example, trap small molecules: https://en.wikipedia.org/wiki/Evanescent_field


The term total is somewhat misleading. Beyond the critical angle the transmitted field is evanescent. However, if the reflecting material is thin enough the evanescent field can couple to propagating modes. This is just like tunneling in quantum mechanics. The skin depth associated with the evanescent field depends on the imaginary part of the dielectric constant and the frequency.


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