In optics, an optical medium is material through which light and other electromagnetic waves propagate. It is a form of transmission medium. The permittivity and permeability of the medium define how electromagnetic waves propagate in it.
The optical medium has an intrinsic impedance, given by
where [math]\displaystyle{ E_x }[/math] and [math]\displaystyle{ H_y }[/math] are the electric field and magnetic field, respectively. In 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 velocity [math]\displaystyle{ c_w = \nu \lambda }[/math], where [math]\displaystyle{ \nu }[/math] is the frequency and [math]\displaystyle{ \lambda }[/math] is the wavelength of the electromagnetic waves. This equation also may be put in the form
where [math]\displaystyle{ \omega }[/math] is the angular frequency of the wave and [math]\displaystyle{ k }[/math] is the wavenumber of the wave. In electrical engineering, the symbol [math]\displaystyle{ \beta }[/math], called the phase constant, is often used instead of [math]\displaystyle{ k }[/math].
The 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.[3]
Original source: https://en.wikipedia.org/wiki/Optical medium.
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