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Is there light tunneling taking place in optically transparent mediums like glass? wherein light travels a larger path in these mediums without interacting with atoms and without any change in velocity, frequency, wavelength or momentum? but just getting affected by the field of atom and following the least resistant path through the medium?

Krups
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  • related question http://physics.stackexchange.com/questions/30325/why-isnt-light-scattered-through-transparency/30330#30330 – anna v Jun 22 '12 at 05:59

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There is no analog of tunneling in transmission through a transparent medium, that's the light analog of the particle phenomenon of entering a region of potential energy.

The direct analog of light tunneling is transmission through a narrow gap between two materials, where you would have total internal reflection on one side of the gap if the other material wasn't there. This was understood in Maxwell theory without quantum mechanics in the 19th century. Even though you have total internal reflection, there is still an evanescent wave outside which allows the light to continue if a new medium which does not require total internal reflection at this angle is just brought within a few wavelengths of the total-internal-reflection point. The photon is going across a region which is forbidden in the geometric optics (classical) limit.

Ron Maimon
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I'm not sure what you mean by light tunneling through an optically transparent medium without interacting. When light propagates through a medium, it does interact with the medium. You can think of a transparent medium to be composed of a lot of tiny dipoles which are driven to oscillate due to the electric field of the light. This sets up a net polarization in the medium which then affects the electric field, changing the velocity of propagation through the medium (or the refractive index).

Light does tunnel through barriers. Imagine a prism such that light enters it and then gets internally reflected through one of the surfaces. Bring another prism, with one of its surface parallel to the internally reflected surface, close to the original prism, such that there is a very thin air-gap between the two surfaces. If the air gap were zero, then its as if there was no interface, and you would observe no internal reflection. If however, the air gap was non-zero but really small (on the order of the wavelength of the light), then some of the evanescent wave would get into the second prism and start propagating in it.

Spot
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  • If light is interacting with atoms of the medium, for example if we consider only single atom and photon, then there are infinite possibilities in which light may be emitted in other direction (scattering) but light travels in a particular direction, pointed by the momentum, if momentum has to be conserved, so as to keep the initial direction, then it can only be bent by the field of atom and not absorbed and remitted, thus photon travelling a longer distance in a denser medium as proved by QED. Similar like electrons through a conductor and superconductor – Krups May 23 '12 at 10:24
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    If you want to think of light propagation in a medium in terms of photon scattering, then you cannot consider just a single atom. Indeed, if a single photon scatters off an atom, then there are infinite possibilities for the scattering. However, a medium has essentially an infinite number of such scatterers and you have to add up the probability amplitudes of all these scattering events. Doing so you find that most of the scattering is in the forward direction. Also, the Kramers-Kronig relations imply that if a medium "bends" light, it has to absorb some if it as well. – Spot May 23 '12 at 14:50