Voigt effect
The Voigt effect describes the magneto-optics, the birefringence in a transparent, gaseous medium at a constant magnetic field perpendicular to the propagation direction of the light. It is stronger than the similar effects as the Cotton -Mouton effect ( in molecules or liquids) and Majorana effect ( in kolloidialen solutions). Together, the three factors form the magnetic analogy to the Kerr effect.
The Voigt effect is named after the German physicist Woldemar Voigt, who described him in 1898 for the first time
The Voigt effect is in the literature often both as a magnetic linear birefringence ( engl. magnetic linear birefringence, MLB ) as well as a magnetic linear dichroism (MLD ) refers. It refers to the effect in part to the real part ( in MLB), and partly on the imaginary part ( in MLD ) of the variation of the complex refractive index.
Description
Light or an electromagnetic wave is a transverse wave of coupled electric and magnetic fields, the vibration planes are perpendicular to each other and to the propagation direction.
The Voigt effect occurs when this polarized electromagnetic wave propagating perpendicular to the magnetic field lines. A polarized electromagnetic wave can be described standing in the form of two orthogonal linearly polarized waves, one speaks of perpendicular and parallel polarized component; this reference is usually to the electric field vector E of the wave. The magnetic field causes the component of the electric field vector oscillates parallel to the magnetic field propagates with a different phase velocity than the vertically vibrating electric field vector. Due to the different phase velocities, the polarization state of the wave changes, it is generally an elliptically polarized wave from a linearly polarized wave.
This phenomenon can be described by the use of two refractive indices and is called birefringence. In the normal birefringence, this is effected by an anisotropic structure of the irradiated material. Otherwise the Voigt effect: This birefringence is caused by a magnetic field and the change of the refractive index n is proportional to the square of the magnetic flux density B:
For optically isotropic materials the following applies:
The change in polarization is also dependent on other variables:
- Phase shift of the wave ...
- Elementary charge ...
- Carrier concentration ...
- Wavelength ...
- Magnetic flux density ...
- Distance in the material ...
- Speed of light ...?
- ... (Complex) refractive index of the material at the respective wavelength without magnetic field
- Voigt ... effective mass ( has a strong crystallographic dependence)
Application
The Voigt effect is used in so-called Voigt filters, one kind of atomic line filter. It is a gas cell to a λ/2-Verzögerungsplatte by the Voigt effect.