Voigt effect

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The Voigt effect is one of a class of effects, resulting in what is called magnetic birefringence or magnetic double refraction. It is a magneto-optical phenomenon with a similar origin to the Faraday effect. In the Faraday effect, the polarization of light can be rotated when passed through a transparent medium to which an external magnetic field is applied. The Voigt effect is similar, but while the Faraday effect is linear in the applied field, the Voigt 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.

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

This effect is utilized in Voigt filters, a type of atomic line filter. In this circumstance, the Voigt effect makes a vapor cell act as a half-wave plate.

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