2
$\begingroup$

When light goes from a more dense medium to a less dense medium, it bends away from the normal, as in the image

pic

When light goes from a less dense medium to a more dense medium it bends towards the normal, as in the pic

pic

But is it possible that light turns all the way around the normal? I think it should be possible as it doesn't violate fermat's principle, or does it? (see the image that follows)

pic

NOTE(1): I have specified the interface in pic 3 so as to show that this is not a case of total internal reflection
NOTE(2): please explain in regards to fermat's principle, as you would to a person just been introduced to ray optics

$\endgroup$
2

2 Answers 2

2
$\begingroup$

For positive refractive indices, it will violate the conservation of momentum (which is used to derive Snell's law).

Also it would violate Fermats principle as there would be a more direct path (eg any normal incidence connecting two opposite points on the path).

$\endgroup$
5
  • $\begingroup$ +1 I was just going to mention the conservation law that leads to Snell's law. $\endgroup$
    – user196418
    Commented May 24, 2019 at 12:03
  • $\begingroup$ Not sure how metamaterials get around this. Potentially they are only negative in the one axis. $\endgroup$ Commented May 24, 2019 at 12:08
  • $\begingroup$ Would you please explain in detail? $\endgroup$ Commented May 24, 2019 at 14:59
  • $\begingroup$ arxiv.org/pdf/physics/0502054.pdf $\endgroup$ Commented May 24, 2019 at 22:35
  • $\begingroup$ Or see wikipedia for Snell's law $\endgroup$ Commented May 24, 2019 at 22:36
0
$\begingroup$

No, this is not possible. Light basically takes the path that requires the least number of wavelengths to get from one point to another (this is a special case of the principle of least action. The wavelength changes according to the material the ray of light is traversing, but it is always a positive number. In the case you suggest, there are always trajectories for which the wavelength count will be smaller than for the one you propose; for example, taking a straight line joining the two ends of the trajectory you propose would give a lower wavelength count, although it would likely not be optimal.

$\endgroup$
2
  • 1
    $\begingroup$ It is for negative refractive index materials physics.stackexchange.com/questions/330915/…. $\endgroup$
    – jinawee
    Commented May 24, 2019 at 11:45
  • $\begingroup$ Omg, that's interesting. Thanks a lot for letting me know that those exist. $\endgroup$
    – Zatrapilla
    Commented May 24, 2019 at 16:48

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.