Optical 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.

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Properties The optical medium has an intrinsic impedance, given by

:$\backslash eta\; =\; \{E\_x\; \backslash over\; H\_y\}$

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:

:$\backslash eta\; =\; \backslash sqrt\{\backslash mu\; \backslash over\; \backslash varepsilon\}\backslash \; .$

For example, in free space the intrinsic impedance is called the characteristic impedance of vacuum, denoted Z₀, and

:$Z\_0\; =\; \backslash sqrt\{\backslash mu\_0\; \backslash over\; \backslash varepsilon\_0\}\backslash \; .$

Waves propagate through a medium with velocity $c\_w\; =\; \backslash nu\; \backslash lambda$, where $\backslash nu$ is the frequency and $\backslash lambda$ is the wavelength of the electromagnetic waves. This equation also may be put in the form

$c\_w\; =\; \{\backslash omega\; \backslash over\; k\}\backslash \; ,$

where $\backslash omega$ is the angular frequency of the wave and $k$ is the wavenumber of the wave. In electrical engineering, the symbol $\backslash beta$, 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 c₀:With ISO 31-5, NIST and the BIPM have adopted the notation c₀.

$c\_0\; =\; \{1\; \backslash over\; \backslash sqrt\{\backslash varepsilon\_0\; \backslash mu\_0\}\}\backslash \; ,$

where $\backslash varepsilon\_0$ is the electric constant and $~\; \backslash mu\_0\; \backslash$ is the magnetic constant.

For a general introduction, see Serway

For a discussion of synthetic media, see Joannopoulus.

(2025). 9780691124568, Princeton University Press. . ISBN 9780691124568

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See also

• Čerenkov radiation
• Electromagnetic spectrum
• Electromagnetic radiation
• Optics
• SI units
• Free space
• Metamaterial
• Photonic crystal
• Photonic crystal fiber

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Notes and references

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