Stark effect

In atomic physics describes the Stark effect (after John Stark, who discovered it in 1913 ), the shift and splitting of atomic or molecular spectral lines in the static electric field. It is the analogue of the Zeeman effect in which segregating spectral lines in the presence of a magnetic field.

Regardless of the Stark effect also in 1913 by the Italian physicist Antonio Lo Surdo ( 1880-1949 ) was discovered. Earlier, unsuccessful attempts to prove the effect, had been taken by Woldemar Voigt in 1899.

Mechanisms

In the quantum mechanical view, the electric field leads to another term in the Hamiltonian (see fine structure ). If the field is sufficiently weak, so this term is in the form

Here, the electrical dipole moment and the electric field strength. One can determine the new energy eigenvalues ​​and states with the help of perturbation theory. The following energy shifts can arise:

Linear Stark effect

The linear Stark effect splits k- fold degenerate energy levels in an electric field, whereby

With parabolic quantum numbers and.

If that atom has a permanent dipole moment, and the energy of the dipole is proportional to the applied field strength:

In the literature, as the condition for the high shift often the degeneration of angular momentum shown in zero field. Since this always occurs together with the degeneracy, this is correct. However, the degeneracy is not directly related to the Stark shift.

Quadratic Stark effect

The square Stark effect causes a shift of the energy levels is proportional to the square of the field strength. It occurs in all atoms and can be explained classically clear: the electric field induced in the atom an electric dipole moment

With the electric polarizability.

This adds to the energy of the free atom following energy:

AC Stark effect

The AC Stark effect (English AC: alternating current = AC), also called dynamic Stark effect, refers to the energy shift due to alternating electric fields, such as light. At high light intensities, however, the application of perturbation theory is no longer allowed and the problem is standardly treated by using the dressed -atom model. In solids, particularly in semiconductors, multi-body interactions lead to some characteristics of the effect that can not be described with the dressed - atom model. Instead, here, the semiconductor Bloch equations may be used.

QCSE

The quantum confined strong effect ( QCSE, such as " limited / narrow-range Stark effect " ) is used in semiconductor physics. It describes the occurring in heterostructures (e.g. laser diodes) Stark effect due to local electric fields, which can be generated by, inter alia, polarization charges. These charges can be generated by the piezoelectric effect due to internal stresses in the combination of different semiconductor materials for example. Forming internal electrical fields through which the optical properties of the material are changed. In addition to a red shift of the emission wavelength part of a reduction in the efficiency of radiative transitions due to the smaller overlap integral by spatial separation of the electron and hole wave functions.

Applications

After the discovery was made the exact determination of the structure of atoms using the Stark effect. Today, the effect is used in the cryogenic single molecule spectroscopy and laser cooling. The latter due to the resulting from the AC Stark shift of dipole forces.