Hi all, I've recently learned some details about refractive indices in different media that I never knew about before. Up until now, I was aware that the speed light travels in a certain medium is dependent on the wavelength of light used. However I wasn't aware that for different kinds of materials, the dependence on wavelength can be higher or lower. For example: (this is what brought up the curiosity in me) when switching from 532 nm light to 1064 nm light, the refractive index of water changes from 1.335 to 1.324. However in a metal, gold for instance, switching from 532 nm to 1064 nm changes the refractive index of gold from 0.467 to 0.285. So it seems that the speed light travels in gold has a much larger dependency on wavelength than water does. I wanted to understand where this comes up, so I figured that calculating the speed of light for a certain medium would go back to the equation c=[εoμo]-1/2. However this time, instead of permittivity and permeability in a vacuum, we would have permittivity and permeability in gold (or whatever material you are curious about). I tried looking around the internet to find how you would calculate these new constants, but I can't figure it out. If anybody could enlighten me that would be cool! Thanks.