Terbium Gallium Garnet (TGG) is the right crystal material for Faraday devices (rotators and isolators).

The Faraday rotator is made up of a TGG rod contained in a specially designed magnet. The polarization of a light beam passing through the device is rotated about the propagation axis.The direction of rotation is only dependent on the direction of the magnetic field and not on the direction of propagation of the light beam.The optical isolator consists of a 45 degree rotator set between two suitably arranged polarizers which allow a light beam to pass through in one direction only. With a combination of excellent properties such as large verdet constant, low light loss, high thermal conductance and high light damage threshold,TGG is the most suitable material for Faraday devices. It is widely used for YAG lasers and Ti:sapphire tunable lasers, ring lasers,etc.