Optical medium
In optics, an optical medium is material through which light and other electromagnetic waves propagate.The permittivity and permeability of the medium define how electromagnetic waves propagate in it.The optical medium has an intrinsic impedance, given by whereIn a region with no electrical conductivity, the expression simplifies to: For example, in free space the intrinsic impedance is called the characteristic impedance of vacuum, denoted Z0, and Waves propagate through a medium with velocityThe propagation velocity of electromagnetic waves in free space, an idealized standard reference state (like absolute zero for temperature), is conventionally denoted by c0:[1] For a general introduction, see Serway[2] For a discussion of synthetic media, see Joannopoulus.