The Verdet constant is an

optical Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behaviour of visible, ultraviole ...

property named after the French physicist

Émile Verdet Marcel Émile Verdet (; 13 March 1824 – 3 June 1866) was a French physicist. He worked in magnetism and optics, editing the works of Augustin-Jean Fresnel. Verdet did much to champion the early theory of the conservation of energy in France th ...

. It describes the strength of 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 ...

for a particular material. For a constant magnetic field parallel to the path of the light, it can be calculated by: :

\theta=V B L

Where

\theta

is the angle between the starting and ending polarizations,

V

is the Verdet constant,

B

is the strength of the magnetic flux density, and

L

is the path length in the material. The Verdet constant of a material is

wavelength In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats. It is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, tro ...

dependent and for most materials is extremely small. It is strongest in substances containing

paramagnetic Paramagnetism is a form of magnetism whereby some materials are weakly attracted by an externally applied magnetic field, and form internal, induced magnetic fields in the direction of the applied magnetic field. In contrast with this behavior, d ...

ion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conven ...

s such as

terbium Terbium is a chemical element with the symbol Tb and atomic number 65. It is a silvery-white, rare earth metal that is malleable, and ductile. The ninth member of the lanthanide series, terbium is a fairly electropositive metal that reacts with wa ...

. The highest Verdet constants in bulk media are found in terbium doped dense flint glasses or in

crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macros ...

s of

terbium gallium garnet Terbium gallium garnet (TGG) is a kind of synthetic garnet, with the chemical composition . This is a Faraday rotator material with excellent transparency properties and is very resistant to laser damage. TGG can be used in optical isolators for l ...

(TGG). These materials have excellent transparency properties and high damage thresholds for

laser A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word "laser" is an acronym for "light amplification by stimulated emission of radiation". The fir ...

radiation. Atomic vapours, however, can have Verdet constants which are orders of magnitude larger than TGG, but only over a very narrow wavelength range. Alkali vapours can therefore be used as an

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 of ...

or as an extremely sensitive

magnetometer 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, o ...

. The Faraday effect is chromatic (i.e. it depends on wavelength) and therefore the Verdet constant is quite a strong function of wavelength. At 632.8 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

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 of ...

s and isolators are adjustable by varying the degree to which the active TGG rod is inserted into the

magnetic field A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to ...

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. Truly

broadband In telecommunications, broadband is wide bandwidth data transmission which transports multiple signals at a wide range of frequencies and Internet traffic types, that enables messages to be sent simultaneously, used in fast internet connections. ...

sources (such as

ultrashort-pulse laser An ultrashort pulse laser is a laser that emits ultrashort pulses of light, generally of the order of femtoseconds to one picosecond. They are also known as ultrafast lasers owing to the speed at which pulses "turn on" and "off"—not to be confus ...

s and the tunable vibronic lasers) will not see the same rotation across the whole wavelength band.

References

{{DEFAULTSORT:Verdet Constant Magneto-optic effects