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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 Z₀, and

$Z_0 = \sqrt{\mu_0 \over \varepsilon_0}\ .$

Waves propagate through a medium with velocity $c w = νλ$ , where $ν$ is the frequency and $λ$ is the wavelength of the electromagnetic waves. This equation also may be put in the form

$c_w = {\omega \over k}\ ,$

where $ω$ is the angular frequency of the wave and $k$ is the wavenumber of the wave. In electrical engineering, the symbol $β$ , 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:^[1]

$c_0 = {1 \over \sqrt{\varepsilon_0 \mu_0}}\ ,$

where $\varepsilon_0$ is the electric constant and $~ \mu_0 \$ is the magnetic constant.

For a general introduction, see Serway^[2] For a discussion of man-made media, see Joannopoulus.^[3]

[edit] Notes and references

^ With ISO 31-5, NIST and the BIPM have adopted the notation c₀.
^ Raymond Serway & Jewett J (2003). Physics for scientists and engineers (6^th Edition ed.). Belmont CA: Thomson-Brooks/Cole. ISBN 0-534-40842-7. http://worldcat.org/isbn/0-534-40842-7.
^ John D Joannopouluos, Johnson SG, Winn JN & Meade RD (2008). Photonic crystals : molding the flow of light (2^nd Edition ed.). Princeton NJ: Princeton University Press. ISBN 978-0-691-12456-8. http://ab-initio.mit.edu/book/.

[edit] See also

[0] With ISO 31-5, NIST and the BIPM have adopted the notation c₀.

[Serway-1] Raymond Serway & Jewett J (2003). Physics for scientists and engineers (6^th Edition ed.). Belmont CA: Thomson-Brooks/Cole. ISBN 0-534-40842-7. http://worldcat.org/isbn/0-534-40842-7.

[Joannopoulos-2] John D Joannopouluos, Johnson SG, Winn JN & Meade RD (2008). Photonic crystals : molding the flow of light (2^nd Edition ed.). Princeton NJ: Princeton University Press. ISBN 978-0-691-12456-8. http://ab-initio.mit.edu/book/.

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