# Two different mediums can have equal index of refraction?

In other words: given a certain medium, is light's phase velocity unique?

• If we consider the complex refractive index vs. the frequency then probably the whole function $n(\omega)$ contains a lot information about the medium, with the absorption lines at the resonances etc; maybe gives enough information to uniquely identify the medium. – Maxim Umansky Oct 19 '14 at 16:05