[1] For a constant magnetic field parallel to the path of the light, it can be calculated as[2] where
The highest Verdet constants in bulk media are found in terbium-doped dense flint glasses or in crystals of terbium gallium garnet (TGG).
These materials have excellent transparency properties and high damage thresholds for laser radiation.
Atomic vapours, however, can have Verdet constants which are orders of magnitude larger than TGG,[3] but only over a very narrow wavelength range.
Many Faraday rotators and isolators are adjustable by varying the degree to which the active TGG rod is inserted into the magnetic field of the device.