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Medium (optics)
 
 
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An optical medium is material through which electromagnetic waves propagate. It is a form of transmission medium
Transmission medium

A transmission medium is a material substance which can wave propagation energy waves. For example, the transmission medium for sound received by the ears is usually air, but solids and liquids may also act as transmission media for sound....
. The permittivity
Permittivity

Permittivity is a physical quantity that describes how an electric field affects, and is affected by a dielectric medium, and is determined by the ability of a material to polarization in response to the field, and thereby reduce the total electric field inside the material....
 and permeability
Permeability (electromagnetism)

In electromagnetism, permeability is the degree of magnetization of a material that responds linearly to an applied magnetic field. Magnetic permeability is typically represented by the Greek letter Mu ....
 of the medium define how electromagnetic waves propagate in it. The medium has an intrinsic impedance, given by
where and are the electric field
Electric field

In physics, the space surrounding an electric charge or in the presence of a time-varying magnetic field has a property called an electric field ....
 and magnetic field
Magnetic field

A magnetism field is a vector field which can exert a magnetic force on moving electric charges and on magnetic dipoles . When placed in a magnetic field, magnetic dipoles tend to align their axes parallel to the magnetic field....
, respectively. In a region with no electrical conductivity
Electrical conductivity

Electrical conductivity or specific conductance is a measure of a material's ability to electrical conduction an electric current. When an electrical potential difference is placed across a conductor, its movable charges flow, giving rise to an electric current....
, the expression simplifies to:



For example, in free space
Free space

In classical physics, free space is a concept of electromagnetic theory, corresponding to a theoretically perfect vacuum, and sometimes referred to as the vacuum of free space....
 the intrinsic impedance is called the characteristic impedance of vacuum, denoted Z0, and



Waves propagate through a medium with velocity , where is the frequency
Frequency

Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency....
 and is the wavelength
Wavelength

In physics, wavelength is the distance between repeating units of a propagating wave of a given frequency. It is commonly designated by the Greek language letter lambda ....
 of the electromagnetic waves.






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An optical medium is material through which electromagnetic waves propagate. It is a form of transmission medium
Transmission medium

A transmission medium is a material substance which can wave propagation energy waves. For example, the transmission medium for sound received by the ears is usually air, but solids and liquids may also act as transmission media for sound....
. The permittivity
Permittivity

Permittivity is a physical quantity that describes how an electric field affects, and is affected by a dielectric medium, and is determined by the ability of a material to polarization in response to the field, and thereby reduce the total electric field inside the material....
 and permeability
Permeability (electromagnetism)

In electromagnetism, permeability is the degree of magnetization of a material that responds linearly to an applied magnetic field. Magnetic permeability is typically represented by the Greek letter Mu ....
 of the medium define how electromagnetic waves propagate in it. The medium has an intrinsic impedance, given by
where and are the electric field
Electric field

In physics, the space surrounding an electric charge or in the presence of a time-varying magnetic field has a property called an electric field ....
 and magnetic field
Magnetic field

A magnetism field is a vector field which can exert a magnetic force on moving electric charges and on magnetic dipoles . When placed in a magnetic field, magnetic dipoles tend to align their axes parallel to the magnetic field....
, respectively. In a region with no electrical conductivity
Electrical conductivity

Electrical conductivity or specific conductance is a measure of a material's ability to electrical conduction an electric current. When an electrical potential difference is placed across a conductor, its movable charges flow, giving rise to an electric current....
, the expression simplifies to:



For example, in free space
Free space

In classical physics, free space is a concept of electromagnetic theory, corresponding to a theoretically perfect vacuum, and sometimes referred to as the vacuum of free space....
 the intrinsic impedance is called the characteristic impedance of vacuum, denoted Z0, and



Waves propagate through a medium with velocity , where is the frequency
Frequency

Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency....
 and is the wavelength
Wavelength

In physics, wavelength is the distance between repeating units of a propagating wave of a given frequency. It is commonly designated by the Greek language letter lambda ....
 of the electromagnetic waves. This equation also may be put in the form where is the angular frequency
Angular frequency

In physics , angular frequency ? is a scalar measure of rotation rate. Angular frequency is the magnitude of the vector quantity angular velocity....
 of the wave and is the wavenumber
Wavenumber

Wavenumber in most physics sciences is a wave property inverse related to wavelength, having SI units of reciprocal metre . Wavenumber is the space analog of frequency, that is, it is the measurement of the number of repeating units of a propagating wave per unit of space....
 of the wave. In electrical engineering
Electrical engineering

Electrical engineering, sometimes referred to as electrical and electronic engineering, is a field of engineering that deals with the study and application of electricity, electronics and electromagnetism....
, the symbol , called the phase constant, is often used instead of .

The propagation velocity of electromagnetic waves in free space
Free space

In classical physics, free space is a concept of electromagnetic theory, corresponding to a theoretically perfect vacuum, and sometimes referred to as the vacuum of free space....
, an idealized standard reference state (like absolute zero
Absolute zero

Absolute zero is a temperature marked by a 0 entropy configuration. It is the coldest temperature theoretically possible, and cannot be reached, by artificial or natural means....
 for temperature), is conventionally denoted by c0:
where is the electric constant
Electric constant

Vacuum permittivity, referred to by international standards organizations as the electric constant, and denoted by the symbol e0, is a fundamental physical constant relating the mechanical quantities to the units for electrical charge, for example, in Coulomb's law....
 and is the magnetic constant.


For a general introduction, see Serway For a discussion of man-made media, see Joannopoulus.

See also

  • Electromagnetic spectrum
    Electromagnetic spectrum

    The electromagnetic spectrum is the range of all possible electromagnetic radiation frequencies. The "electromagnetic spectrum" of an object is the characteristic distribution of electromagnetic radiation from that particular object....
  • Electromagnetic radiation
    Electromagnetic radiation

    Electromagnetic radiation takes the form of wave propagation waves in a vacuum or in matter. EM radiation has an electric field and magnetic field component which oscillate in phase perpendicular to each other and to the direction of energy Wave propagation....
  • Optics
    Optics

    Optics is the study of the behavior and properties of light including its optical phenomena with matter and its imaging by optical instruments....
  • SI units
  • Free space
    Free space

    In classical physics, free space is a concept of electromagnetic theory, corresponding to a theoretically perfect vacuum, and sometimes referred to as the vacuum of free space....
  • Photonic crystal
    Photonic crystal

    Photonic crystals are periodic optical nanostructures that are designed to affect the motion of photons in a similar way that periodicity of a semiconductor crystal affects the motion of electrons....
  • Photonic crystal fiber
  • Cerenkov radiation