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Properties

The optical medium has an intrinsic impedance, given by

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

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

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

where 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 {\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 c0:¹

c 0 = 1 ε 0 μ 0   , {\displaystyle c_{0}={1 \over {\sqrt {\varepsilon _{0}\mu _{0}}}}\ ,} where ε 0 {\displaystyle \varepsilon _{0}} is the electric constant and   μ 0   {\displaystyle ~\mu _{0}\ } is the magnetic constant.

For a general introduction, see Serway² For a discussion of synthetic media, see Joannopoulus.³

Types

1. Homogeneous medium vs. heterogeneous medium
2. Transparent medium vs. opaque body

• • Translucent medium

See also

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

Notes and references

References

1. With ISO 31-5, NIST and the BIPM have adopted the notation c0. /wiki/ISO_31-5 ↩

2. Raymond Serway & Jewett J (2003). Physics for scientists and engineers (6th ed.). Belmont CA: Thomson-Brooks/Cole. ISBN 0-534-40842-7. 0-534-40842-7 ↩

3. John 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. 978-0-691-12456-8 ↩