Terbium gallium garnet (TGG) is a kind of synthetic

garnet Garnets () are a group of silicate minerals that have been used since the Bronze Age as gemstones and abrasives. All species of garnets possess similar physical properties and crystal forms, but differ in chemical composition. The different s ...

, with the chemical composition . This is a

Faraday rotator A Faraday rotator is a polarization rotator based on the Faraday effect, a magneto-optic effect involving transmission of light through a material when a longitudinal static magnetic field is present. The state of polarization (such as the axis o ...

material with excellent transparency properties and is very resistant to laser damage. TGG can be used in

optical isolator An optical isolator, or optical diode, is an optical component which allows the transmission of light in only one direction. It is typically used to prevent unwanted feedback into an optical oscillator, such as a laser cavity. The operation ...

s for laser systems, in

optical circulator An optical circulator is a three- or four-port optical device designed such that light entering any port exits from the next. This means that if light enters port 1 it is emitted from port 2, but if some of the emitted light is reflected back to t ...

s for fiber optic systems, in

optical modulator An optical modulator is a device which is used to modulate a beam of light. The beam may be carried over free space, or propagated through an optical waveguide ( optical fibre). Depending on the parameter of a light beam which is manipulated, mod ...

s, and in current and

magnetic field sensors A magnetometer is a device that measures magnetic field or magnetic dipole moment. Different types of magnetometers measure the direction, strength, or relative change of a magnetic field at a particular location. A compass is one such device, on ...

. TGG has a high

Verdet constant The Verdet constant is an optical property named after the French physicist Émile Verdet. It describes the strength of the Faraday effect for a particular material. For a constant magnetic field parallel to the path of the light, it can be calcu ...

which results in the

Faraday effect The Faraday effect or Faraday rotation, sometimes referred to as the magneto-optic Faraday effect (MOFE), is a physical magneto-optical phenomenon. The Faraday effect causes a polarization rotation which is proportional to the projection of the m ...

. The Verdet constant increases substantially as the mineral approaches cryogenic temperatures. The highest Verdet constants are found in terbium doped dense

flint glass Flint glass is optical glass that has relatively high refractive index and low Abbe number (high dispersion). Flint glasses are arbitrarily defined as having an Abbe number of 50 to 55 or less. The currently known flint glasses have refractiv ...

es or in crystals of TGG. The Faraday effect is

chromatic Diatonic and chromatic are terms in music theory that are most often used to characterize scales, and are also applied to musical instruments, intervals, chords, notes, musical styles, and kinds of harmony. They are very often used as a pair, ...

(i.e. it depends on wavelength) and therefore the Verdet constant is quite a strong function of wavelength. At 632 nm, the Verdet constant for TGG is reported to be , whereas at 1064 nm it falls to . This behavior means that the devices manufactured with a certain degree of rotation at one wavelength, will produce much less rotation at longer wavelengths. Many

s and isolators are adjustable by varying the degree to which the amount of the Faraday rotator material is inserted into the magnetic field of the device. In this way, the device can be tuned for use with a range of lasers within the design range of the device.

References

Synthetic minerals Oxides Terbium compounds Gallium compounds Nonlinear optical materials {{Engineering-stub

See also

References