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I Is there refraction upon frustrated total internal reflection

  1. Nov 2, 2018 #1
    In frustrated total internal reflection, is there refraction corresponding to the refractive index difference between the first and third medium or does the light continue in straight line as it is usually depicted in graphic representations of the frustrated total internal reflection?
  2. jcsd
  3. Nov 3, 2018 #2


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    I believe the answer to your question is no. Refraction occurs because of the change in phase-time-distance relations when the wave passes across the interface between mediums. In total internal reflection the relationship between phase, time and distance remains the same and thus the reflected wave must be a symmetric reflection of the incident wave.
  4. Nov 3, 2018 #3
    You meant the transmitted wave at the end, right? For clarity, I was asking if the ray transmitted through the gap is "bent" (refracted) in relation to the ray in the first medium if there's a difference in refractive index between the two higher index media
    Last edited: Nov 3, 2018
  5. Nov 3, 2018 #4


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    I see. I missed the "frustrated" component. Between the mediums of the same index of refraction there will be no net angular refraction. Again this is necessary due to continuity of the phase-time-position relationships of the waves. You may have a lateral offset of the waves (offset parallel to wave front) due to the shift in phase as the light traverses the intermediate gap but the direction can't change.

    Short of actually bending space-time, i.e. considering gravitational effects, the only way the beam could change direction between regions of equivalent index of refraction with whatever intermediate medium you might imagine provided it's uniformly coplanar (no prisms) would be for there to be a frequency shift.
  6. Nov 4, 2018 #5


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    If extending the FTIR situation to prisms is valid, this might be informative.
    (about 40% down the page from: http://blog.teachersource.com/2011/11/26/two-prisms-four-demos/)

    Isaac Newton also wondered if the colors of the spectrum could be recombined to again make white light. To do this he used a second prism arranged as shown. He proved that this was possible. What’s interesting is that the light beams exiting the second prism are not on the same line, but they are PARALLEL. And, because the slit is not infinitely narrow, these beams are not infinitely narrow and therefore can mix to create white light.




  7. Nov 11, 2018 at 4:27 PM #6


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    So far as I understand it, evanescent waves do not convey information and so do not have a defined speed of propagation. Therefore, I expect zero time delay across the gap between the two prisms. The following paper talks about this:-
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