Physics:Optical medium
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
- [math]\displaystyle{ \eta = {E_x \over H_y} }[/math]
where [math]\displaystyle{ E_x }[/math] and [math]\displaystyle{ H_y }[/math] are the electric field and magnetic field, respectively. In a region with no electrical conductivity, the expression simplifies to:
- [math]\displaystyle{ \eta = \sqrt{\mu \over \varepsilon}\ . }[/math]
For example, in free space the intrinsic impedance is called the characteristic impedance of vacuum, denoted Z0, and
- [math]\displaystyle{ Z_0 = \sqrt{\mu_0 \over \varepsilon_0}\ . }[/math]
Waves propagate through a medium with velocity [math]\displaystyle{ c_w = \nu \lambda }[/math], where [math]\displaystyle{ \nu }[/math] is the frequency and [math]\displaystyle{ \lambda }[/math] is the wavelength of the electromagnetic waves. This equation also may be put in the form
- [math]\displaystyle{ c_w = {\omega \over k}\ , }[/math]
where [math]\displaystyle{ \omega }[/math] is the angular frequency of the wave and [math]\displaystyle{ k }[/math] is the wavenumber of the wave. In electrical engineering, the symbol [math]\displaystyle{ \beta }[/math], called the phase constant, is often used instead of [math]\displaystyle{ k }[/math].
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]
- [math]\displaystyle{ c_0 = {1 \over \sqrt{\varepsilon_0 \mu_0}}\ , }[/math]
- where [math]\displaystyle{ \varepsilon_0 }[/math] is the electric constant and [math]\displaystyle{ ~ \mu_0 \ }[/math] is the magnetic constant.
For a general introduction, see Serway[2] For a discussion of synthetic media, see Joannopoulus.[3]
Types
- Homogeneous medium vs. heterogeneous medium
- 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
- ↑ With ISO 31-5, NIST and the BIPM have adopted the notation c0.
- ↑ Raymond Serway; Jewett J (2003). Physics for scientists and engineers (6th ed.). Belmont CA: Thomson-Brooks/Cole. ISBN 0-534-40842-7. https://archive.org/details/physicssciengv2p00serw.
- ↑ 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. http://ab-initio.mit.edu/book/.
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