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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

• See also

• Notes and references

The optical medium has an intrinsic impedance, given by

η η = E x H y {\displaystyle \eta ={E_{x} \over H_{y}}}

where E x {\displaystyle E_{x}} and H y {\displaystyle H_{y}} are the electric field and magnetic field, respectively. In a region with no electrical conductivity, the expression simplifies to:

η η = μ μ ε ε . {\displaystyle \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 = μ μ 0 ε ε 0 . {\displaystyle Z_{0}={\sqrt {\mu _{0} \over \varepsilon _{0}}}\ .}

Waves propagate through a medium with velocity c w = ν ν λ λ {\displaystyle c_{w}=\nu \lambda } , where ν ν {\displaystyle \nu } is the frequency and λ λ {\displaystyle \lambda } is the wavelength of the electromagnetic waves. This equation also may be put in the form

c w = ω ω k , {\displaystyle c_{w}={\omega \over k}\ ,}

where ω ω {\displaystyle \omega } is the angular frequency of the wave and k {\displaystyle k} is the wavenumber of the wave. In electrical engineering, the symbol β β {\displaystyle \beta } , called the phase constant, is often used instead of k {\displaystyle 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:cite-ref-1[1]

c 0 = 1 ε ε 0 μ μ 0 , {\displaystyle c_{0}={1 \over {\sqrt {\varepsilon _{0}\mu _{0}}}}\ ,}

where ε ε 0 {\displaystyle \varepsilon _{0}} is the electric constant and μ μ 0 {\displaystyle ~\mu _{0}\ } is the magnetic constant.

For a general introduction, see Serwaycite-ref-serway-2-0[2] For a discussion of synthetic media, see Joannopoulus.cite-ref-joannopoulos-3-0[3]

• Čerenkov radiation

• Electromagnetic spectrum

• Electromagnetic radiation

• Optics

• SI units

• Free space

• Metamaterial

• Photonic crystal

• Photonic crystal fiber

cite-note-11. ↑ With ISO 31-5, NIST and the BIPM have adopted the notation c0.

cite-note-serway-22. ↑ citerefraymond-serwayjewett-j2003Raymond Serway & Jewett J (2003). Physics for scientists and engineers (6th ed.). Belmont CA: Thomson-Brooks/Cole. ISBN 0-534-40842-7.

cite-note-joannopoulos-33. ↑ citerefjohn-d-joannopouluosjohnson-sgwinn-jnmeade-rd2008John D Joannopouluos; Johnson SG; Winn JN; Meade RD (2008). Photonic crystals : molding the flow of light (2nd ed.). Princeton NJ: Princeton University Press. ISBN 978-0-691-12456-8.