Should phase velocity use the real or modulus of complex refractive index?

[Niles]

Hi

When we have a complex index of refraction, the real part determines the phase-change of the incoming wave and the complex part attenuates the wave. When we e.g. want to find the phase velocity using v = c/n, when should we use the real part of n or the modulus of n?


Niles.

 

[DrDu]

Hence a monochromatic wave would be $$\exp(i\omega(nx/c-t) =\exp(-\omega \Im(n)x/c)\exp(i\omega\Re(n)x/c-t)$$.So points of constant phase are determined by Re(n)x/c-t=const which move with the speed c/Re(n).

 

[Niles]

I see, thanks!