Does a wave experiencing a total internal reflection penetrate the medium in any way?

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In a classical electrodynamics picture there is an exponentially dampened wave penetrating the medium with the smaller index of refraction. See e.g. http://en.wikipedia.org/wiki/Total_internal_reflection. This wave can indeed be detected. The easiest way to see this is by bringing a third optical surface close to the interface. There will be non-zero transmission across the gap even at distances >0. The two interfaces just have to be close enough (on the order of a few wavelengths).

The Feynman lectures explain it beautifully: http://www.feynmanlectures.caltech.edu/II_33.html#Ch33-S6

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neverneve
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neverneve

Updated on October 08, 2020

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  • neverneve
    neverneve about 3 years

    Let me explain my concern usingn this picture: total internal reflection

    At the point of total internal reflection does a fraction of the wave get into medium 2? I would imagine it should happen because of the uncertainty principle or maybe quantum tunneling, but these are just wild guesses. In other words, if the wave was light, medium 1 water and medium 2 air, if we put a light detecting device just above the point of totalinternal reflection in the picture, would it occasionaly detect a photon? And if yes, does it happen because of quantum mechanics, or maybe it can be explained using the classical model of light taught in high schools?

    • CuriousOne
      CuriousOne about 9 years
      In a classical electrodynamics picture there is an exponentially dampened wave penetrating the medium with the smaller index of refraction. See e.g. en.wikipedia.org/wiki/Total_internal_reflection. This wave can indeed be detected. The easiest way to see this is by bringing a third optical surface close to the interface. There will be non-zero transmission across the gap even at distances >0. The two interfaces just have to be close enough (on the order of a few wavelengths).
    • Admin
      Admin about 9 years
      @CuriousOne: How about making that into an answer?
    • dmckee --- ex-moderator kitten
      dmckee --- ex-moderator kitten about 9 years
      Useful search phase "The frustration of total internal reflection".
  • Arvind Shankar
    Arvind Shankar about 9 years
    BTW, this is also closely analogous to quantum-mechanical tunneling.
  • Jon Custer
    Jon Custer about 9 years
    This is usually called an evanescent wave. I recall it being a standard E&M lab, using (low power) microwaves and paraffin blocks/prisms for TIR and coupling to the detector. Once set up, no power flows in the evanescent wave, so no worries on energy conservation.
  • neverneve
    neverneve about 9 years
    Does this phenomenon occur for all waves (e.g. a sound wave) or only electromagnetic waves?
  • CuriousOne
    CuriousOne about 9 years
    @neverneve: Total internal reflection can occur for sound waves, as well, and it is of importance for submarine warfare and seems to play a role in the way whales navigate the oceans (the reflecting layer is a thermocline, i.e. a zone of rapid temperature change). A similar phenomenon occurs in the atmosphere, which has been used in the past to acoustically detect nuclear explosions (before a satellite network was built). I have to assume the evanescent wave is also universal and should happen with longitudinal waves just as well as with transversal ones.