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Forum: Processes Involving Optical Photons
Re: Question Faster Than Light Photons? (Joel Long)
Re: More Re: Faster Than Light Photons? (Joel Long)
Re: More Re: Faster Than Light Photons? (Joel Long)
Date: 13 Jul, 2012
From: Gumplinger Peter <Gumplinger Peter>

Hi Joel,

Sorry, I meant to answer your post when you first posted it but 'it fell under the radar'.

You found the reason why you are getting 'faster than light photons'. You are specifying a dielectric with an index of refraction <1. Optical photons will not travel inside aluminum; not very far into the volume anyway, before they are either absorbed or reflected. You may assign a REAL and IMAGINARY index of reflection to your Al surface (see the LXe example) which are then used to calculate the reflectivity of the surface.

But this is not allowed:

  G4double refractiveIndexAlMy[numEntriesAlMy] = {0.8734,0.7278,0.6079,0.52135,0.39877};
propTableAluminizedMylar->AddProperty("RINDEX",energiesAlMy,refractiveIndexAlMy,numEntriesAlMy);

> My understanding was that the group velocity *could* be greater than the
> speed of light,

That's news to me...

> and I am reasonably confident in my source for the
> refractive indices of Aluminum.

Your source is probably specifying the real and imaginary part of the metal's index of refraction. If you use that as explained in LXe example, you'll get G4 to calculate the reflectivity of this surface (dielectric_metal)

> 
> Does "group velocity" mean something different in Geant4 than I think it
> does?

No, its meaning in G4 is the same as those in text books.

> Should I simply force my refractive indices to 1 if they are
> actually less than 1?

Do you think it is physical to track optical photons in a metal?

Peter

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1 Feedback: Re: Faster Than Light Photons?   (Joel Long - 16 Jul, 2012)
(_ Feedback: Re: Faster Than Light Photons?   (Gumplinger Peter - 16 Jul, 2012)
(_ Idea: Re: Faster Than Light Photons?   (Erik Dietz-Laursonn - 14 Sep, 2012)
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