Optical medium explained

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

The optical medium has an intrinsic impedance, given by

η = {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:η = \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} = \nu λ , where \nu is the frequency and λ is the wavelength of the electromagnetic waves. This equation also may be put in the formc _{w} = {\omega \over k} , 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 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 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

1. With ISO 31-5, NIST and the BIPM have adopted the notation c₀.
2. Book: Raymond Serway . Jewett J . amp . Physics for scientists and engineers . 6th . 2003 . Thomson-Brooks/Cole . Belmont CA . 0-534-40842-7 . registration.
3. Book: John D Joannopouluos . Johnson SG . Winn JN . Meade RD . Photonic crystals : molding the flow of light. 2nd. 2008. Princeton University Press. Princeton NJ. 978-0-691-12456-8.