An **optical medium** is material through which 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 medium has an *intrinsic impedance*, given by

- $\eta ={E_{x} \over H_{y}}$

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:

- $\eta ={\sqrt {\mu \over \varepsilon }}\ .$

For example, in free space the intrinsic impedance is called the characteristic impedance of vacuum, denoted *Z*_{0}, and

- $Z_{0}={\sqrt {\mu _{0} \over \varepsilon _{0}}}\ .$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:
- $\eta ={\sqrt {\mu \over \varepsilon }}\ .$

For example, in free

For example, in free space the intrinsic impedance is called the characteristic impedance of vacuum, denoted *Z*_{0}, and

- ${\displaysty$
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

- $c_{w}={\omega \over k}\ ,$

where $\ome$

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}:^{[1]}

- $c}_{0}=\frac{1}{\sqrt{{\mathrm{\epsilon <The\; propagation\; velocity\; of\; electromagnetic\; waves\; infree\; space,\; an\; idealized\; standard\; reference\; state\; (likeabsolute\; zerofor\; temperature),\; is\; conventionally\; denoted\; byc0:[1]For\; a\; general\; introduction,\; see\; Serway[2]For\; a\; discussion\; of\; synthetic\; media,\; see\; Joannopoulus.[3]Types\; of\; optical\; mediums(adsbygoogle\; =\; window.adsbygoogle\; ||\; []).push(\{\});Site\; MapHow\; To\; Use\; theinfolist.comThe\; "Did\; you\; know"\; GameHow\; To\; Research\; a\; Report,\; Essay\; or\; TopicHOMEContent\; is\; CopyleftWebsite\; design,\; code,\; and\; AI\; is\; Copyrighted\; (c)\; 2014-2017\; by\; Stephen\; PayneConsider\; donating\; to\; Wikimedia}}_{}}$