kunkmiester wrote:What's the difference between momentum and velocity(?) here?That is that evanescent wave photons can, in some circumstances have superluminal momentum.

Of course you know that momentum in general is given by p = m*v, so p is velocity multiplied by a mass. Here we are looking at a mathematical result in an area of optics very unfamiliar to most. This mathematical result is couched in terms of momentum, not mass, not velocity but the product of mass and velocity. My education and experience is insufficient to allow me to assume knowledge of evanescent photon mass in order to extract information about velocity and similarly insufficient to assume knowledge about velocity to extrct information about mass.

http://en.wikipedia.org/wiki/Photon Wikipedia discusses photon momentum at some length. Momentum is given by p = hf/c where h is Planck's constant, f is frequency and c, the speed of light. But evanescent waves are expotentially decaying waves with (to my knowledge) no real frequency so I can't use this classic result to extract information about evanescent wave photon mass. Maybe someone else knows where this line of reasoning leads, not me.

And maybe there is an answer within the details of the mathematical derivation. One could look there.