Cotton mouton effect

The Cotton-Mouton effect is a magneto-optical effect. It describes the optical birefringence caused by a (strong) external magnetic field when the light propagates perpendicular to the direction of the magnetic field in normally optically isotropic materials; it is therefore also called magnetic birefringence .

A comparable electrical effect is the Kerr effect , in which the strength of the effect also depends on the square of the strength of the field, which is electrical in the Kerr effect.

history

The Cotton-Mouton effect was discovered in 1907 by Aimé Auguste Cotton and Henri Mouton in nitrobenzene and a short time later it was also demonstrated in other organic liquids (e.g. benzene and toluene ).

description

The prerequisite are magnetically polar molecules in the material - they have an electrical and magnetic anisotropy - which are forced into alignment by the magnetic field and thus change the transmission behavior of light (generally electromagnetic waves, including microwaves, etc.). The effect occurs mainly in liquids and is much stronger than the Voigt effect or Majorana effect . It can best be observed with polarized light whose plane of polarization is inclined by 45 ° in relation to the magnetic field. In this case the effect (the difference in phase velocity ) is maximized by the components of the light lying perpendicular or parallel to the magnetic field. The emerging light is elliptically polarized in this case.

${\displaystyle \Delta n=C\ \lambda \ H^{2}}$

It is the Cotton-Mouton constant which depends on the material, wavelength and temperature, and z. B. with nitrobenzene is 3.81 × 10 ⁻¹⁴  A ⁻² m (at room temperature and a wavelength of λ ₀  = 589.3 nm). However , only the contribution perpendicular to the direction of propagation of the light is included as the field strength . ${\displaystyle C}$ ${\displaystyle H}$

Depending on the angle of incidence of the light, the Cotton-Mouton effect also occurs together with the Faraday effect . It can be used for the optical measurement of the magnetic field strength (e.g. with special polarimeters ).

See also

• magneto-optic Kerr effect
• Cotton effect

literature

• M. Freiser: A survey of magnetooptic effects . In: Magnetics, IEEE Transactions on . tape 4 , no. 2 , 1968, p. 152-161 .
• C. Rizzo, A. Rizzo, DM Bishop: The Cotton-Mouton effect in gases: experiment and theory . In: Int. Rev. in Phys. Chem . tape 16 , 1997, pp. 81-111 .
• AD Buckingham, JA Pople: A Theory of Magnetic Double Refraction . In: Proceedings of the Physical Society. Section B . tape 69 , 1956, pp. 1133-1138 .
• Hasan-Nuri Blachnik: Investigation of the Cotton-Mouton effect in the isotropic phase of liquid-crystalline substances. Dissertation, University of Siegen, Department 8, 1999 ( online in the German National Library ).

Individual evidence

1. ↑ AA Cotton, H. Mouton: Nouvelle propriété optique (biréfringence magnétique) de certains liquides organiques non colloidaux . In: Comptes Rendus hebdomadaires of séances de l'Académie des Sciences Paris . No. 145 , 1907, pp. 229-231 .
2. ↑ AA Cotton, H. Mouton: Sur la biréfringence magnétique des liquides organiques . In: Comptes Rendus hebdomadaires of séances de l'Académie des Sciences Paris . No. 145 , 1907, pp. 870-872 .
3. ^ Herbert Daniel: Physics. Volume 3: Optics, Thermodynamics, Quanta . Gruyter, 2002, ISBN 978-3-11-016142-7 .