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Hanle effect

(zero-field level crossing)
(effect of magnetic field on the polarization of emitted photons)

The Hanle effect is an effect of a magnetic field on the electromagnetic radiation (EMR) emitted by atoms/molecules within that magnetic field. In contrast, Faraday rotation is an effect caused by a magnetic field on EMR passing through, i.e., following its emission. The Hanle effect is on the direction and intensity of linear polarization and is of use in determining the direction and strength of the field. However the effect caused by the field-strength flattens, i.e., above some strength threshold, there is little change in the effect, a regime termed the saturated Hanle effect, in which the effect is not a practical means of determining a precise field strength.

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