The Voigt Effect, is one of a class of effects, resulting in what is called magnetic birefringence

Birefringence

Birefringence, or double refraction, is the decomposition of a ray of light into two rays when it passes through certain anisotropic materials, such as crystals of calcite or boron nitride. The effect was first described by the Danish scientist Rasmus Bartholin in 1669, who saw it in calcite...

, or magnetic double refraction. It is a magneto-optical phenomenon with a similar origin to the Faraday effect

Faraday effect

In physics, the Faraday effect or Faraday rotation is a Magneto-optical phenomenon, that is, an interaction between light and a magnetic field in a medium...

. In the Faraday effect, the polarization of light can be rotated when passed through a transparent medium to which an external magnetic field

Magnetic field

A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...

 is applied. The Voigt Effect is similar, but while the Faraday effect is linear in the applied field, this effect is quadratic. This quadratic scaling stems from an arrangement whereby the external magnetic field is applied at right angles to the direction of propagation. In this case, all the effects that are proportional to the magnetic field vanish. The Voigt effect was discovered in 1902 by Woldemar Voigt

Woldemar Voigt

Woldemar Voigt was a German physicist, who taught at the Georg August University of Göttingen. Voigt eventually went on to head the Mathematical Physics Department at Göttingen and was succeeded in 1914 by Peter Debye, who took charge of the theoretical department of the Physical Institute...

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The term Voigt effect is usually reserved for the observation of the aforementioned polarization shift when a vapor

Vapor

A vapor or vapour is a substance in the gas phase at a temperature lower than its critical point....

 plays the role of the transparent medium. When a liquid plays this role, the effect is much stronger (i.e. the proportionality to the square of the magnetic field is greater), and is known as the Cotton-Mouton effect

Cotton-Mouton effect

In physical optics, the Cotton–Mouton effect refers to the double refraction of light in a liquid in the presence of a constant transverse magnetic field. It is a similar but stronger effect than the Voigt effect...

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This effect is utilized in Voigt filters, a type of Atomic line filter

Atomic line filter

An atomic line filter is an advanced optical band-pass filter used in the physical sciences for filtering electromagnetic radiation with precision, accuracy, and minimal signal strength loss...

. In this circumstance, the Voigt Effect makes a vapor cell act as a half wave plate

Wave plate

A wave plate or retarder is an optical device that alters the polarization state of a light wave travelling through it.- Operation :A wave plate works by shifting the phase between two perpendicular polarization components of the light wave. A typical wave plate is simply a birefringent crystal...

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