medium (optics)

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.

Properties

The optical medium has an '' intrinsic impedance'', given by
::$\eta =$
where $E_x$ and $H_y$ are the electric field and magnetic field, respectively.
In a region with no electrical conductivity, the expression simplifies to:

::$\eta = \sqrt\ .$

For example, in free space the intrinsic impedance is called the characteristic impedance of vacuum, denoted ''Z''₀, and

::$Z_0 = \sqrt\ .$

Waves propagate through a medium with velocity $c_w = \nu \lambda$, where $\nu$ is the frequency and $\lambda$ is the wavelength of the electromagnetic waves. This equation also may be put in the form
:$c_w = \ ,$
where $\omega$ is the angular frequency of the wave and $k$ is the wavenumber of the wave. In electrical engineering, the symbol $\beta$, called the '' phase constant'', is often used instead of $k$.

The propagation velocity of electromagnetic waves in free space, an idealized standard reference state (like absolute zero for temperature), is conventionally denoted by ''c''₀:With ISO 31-5, NIST and the BIPM have adopted the notation ''c''₀.
:$c_0 = \ ,$
:where $\varepsilon_0$ is the electric constant and $~ \mu_0 \$ is the magnetic constant.

For a general introduction, see Serway

For a discussion of synthetic media, see Joannopoulus.

See also

* ÄŒerenkov radiation
*Electromagnetic spectrum
*Electromagnetic radiation
*Optics
* SI units
* Free space
* Metamaterial
* Photonic crystal
*Photonic crystal fiber

Notes and references

{{DEFAULTSORT:Medium
Optics
Electric and magnetic fields in matter