Spectral linewidth

The line width is the width of the frequency or wavelength interval or that is covered by a spectral line in the spectrum. The phenomenon was discovered in optical spectra, but also occurs in all spectra of any other types of radiation. In quantum physics (eg, unstable elementary particles), the line width is often expressed by the energy uncertainty or " decay width ", where the Planck constant, and is. Shown is generally the full width at half maximum, i.e. the interval on the profile of the line under consideration, in which the spectral intensity is higher than half the maximum value.

If the observed radiation from many independent sources, one distinguishes the homogeneous linewidth, which already has every single issuer of the inhomogeneous linewidth, which could be reduced by a more accurate selection among issuers. The causes of the homogeneous line width should be mentioned in addition to the basic energy uncertainty of all unstable systems external disturbances such clashes of issuers and Doppler shift due to their random motion.

Natural linewidth

According to quantum mechanics, a physical system if it has a sharply defined energy, in time do not change. Systems that spontaneously decompose or produce radiation, therefore have a basic energy uncertainty (see energy-time uncertainty relation ), their radiation, the corresponding natural linewidth. This is true in general, equally, for example, for elementary particles, radioactive or excited nuclei, excited atoms, molecules. The shape corresponds to a Cauchy distribution, which is also known as the resonance curve or Lorentzian line in physics. Is the decay constant ( transition probability per Zeiteineinheit ), then the service life, i.e., the mean residence time of the future system in the initial state, and its energy spread. The shape resembles this context, the heisenberg 's uncertainty relation and is therefore also known as energy-time uncertainty relation.

In elementary particle physics, this relationship for the experimental determination of extremely short lifetimes will be used. For example arises when Z0 boson from the decay width of the lifetime - the shortest one has yet been found. In optics, the natural line width is directly related to the coherence length.

One can model the natural linewidth using a Lorentz oscillator.

Line broadening

Certain effects, there is a line broadening. The main reasons for an observed line broadening can be the Doppler broadening and pressure broadening.