Le Forgeron <jgr### [at] freefr> wrote:
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> The refraction is the propagation of the EM wave inside the material.
> The positive IOR (IOR>0) might be used to keep the information that the
> EM wave is moving from zone A made of material to zone B made of air (or
> whatever). Same for the opposite, moving from B to A.
> That's refraction. So far so good.
> Now, if I try to imagine your negatif IOR (really, IOR < 0 ? not just
> IOR < 1 ?) as an interface which when encountered by the EM wave send
> the EM wave back in the zone it is coming from, it is not what I would
> call refraction (usually it's called reflection).
> There is of course the classical "total reflection angle" due to
> refraction, but that's only a side effect.
>
> Please note also that even an IOR < 1 would be quite puzzling: it would
> means that light would travel faster than in the void when inside this
> material (faster than c). it would be an interesting universe.
> (especially if the information can be made to travel with the
> corresponding EM wave)... Nahhh, just dreaming.
> There is also a possible usage for the sign of the IOR, which could be
> an oversimplification of the phase change/polarisation of a signal.
> Assuming a clockwise rotation of E toward M, going thru one "negatif
> ior" material could end up with an opposite rotation (anticlockwise).
>
> Now, maybe your "metamaterial" is just a mirror with subsurface
> scattering/refraction ? A kind of variable angle of reflection ?
>
> [end of questionning]

The refractive index n is defined as n^2=permittivity*permeability, so n=+/-
sqrt(permittivity*permeability) (in reality, it's even more complicated).
Hence the negative sign in some cases.
Let's consider an interface between two "normal" materials. An incident beam
coming from material 1 which has a smaller n than material 2 is refracted
towards the surface normal in material 2 according to Snell's law
sin(theta1)/sin(theta2)=n2/n1. The refracted beam propagates "on the other
side"  of the surface normal than the incident beam.
Now, if you replace material 2 by a "metamaterial" with n2<0, the refracted
beam propagates "on the same side" of the surface normal as the incident
beam. That's what would be weird to look at!
Another strange thing in a metamaterial is that the group velocity of a wave
is antiparallel to its propagation direction, the wave vector k is
antiparallel to the Poynting vector S. S determines the overall energy flow
as well as the propagation direction, so that's consistent with the
conservation of energy, thanks Tom York!

If you don't believe me, google "metamaterials", there is lot's of stuff.

So, back to my problem, has anybody any idea of where the IOR is implemented
in POV-ray? Or what can I do to be able to have a negative sign for the
IOR?

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