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

η=ExHydisplaystyle eta =E_x over H_y

where Exdisplaystyle E_x and Hydisplaystyle H_y are the electric field and magnetic field, respectively.
In a region with no electrical conductivity, the expression simplifies to:

η=με .displaystyle eta =sqrt mu over varepsilon .

For example, in free space the intrinsic impedance is called the characteristic impedance of vacuum, denoted Z₀, and

Z0=μ0ε0 .displaystyle Z_0=sqrt mu _0 over varepsilon _0 .

Waves propagate through a medium with velocity cw=νλdisplaystyle c_w=nu lambda , where νdisplaystyle nu is the frequency and λdisplaystyle lambda is the wavelength of the electromagnetic waves. This equation also may be put in the form

cw=ωk ,displaystyle c_w=omega over k ,

where ωdisplaystyle omega is the angular frequency of the wave and kdisplaystyle k is the wavenumber of the wave. In electrical engineering, the symbol βdisplaystyle beta , called the phase constant, is often used instead of kdisplaystyle 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]

c0=1ε0μ0 ,displaystyle c_0=1 over sqrt varepsilon _0mu _0 ,

where ε0displaystyle varepsilon _0 is the electric constant and  μ0 displaystyle ~mu _0 is the magnetic constant.

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

Types of optical mediums[edit]

1. 
   Homogeneous medium


2. Heterogeneous medium


3. 
   Transparent medium


4. 
   Translucent medium


5. 
   Opaque body

Notes and references[edit]

See also[edit]

• Čerenkov radiation


• Electromagnetic spectrum


• Electromagnetic radiation


• Optics


• SI units


• Free space


• Metamaterial


• Photonic crystal


• Photonic crystal fiber