Aimé Cotton

Aimé Auguste Cotton

Aimé Auguste Cotton (born October 9, 1869 in Bourg-en-Bresse , † April 16, 1951 in Sèvres ) was a French physicist who is known for studying the interaction of light with chiral molecules. In the absorption bands of these molecules he discovered large values ​​of optical rotational dispersion (ORD), or the variation of the optical rotation as a function of wavelength ( Cotton-Mouton effect ), as well as circular birefringence or differences in absorption between right and left circularly polarized Light ( circular dichroism ).

life and work

Aimé Cotton was born on October 9, 1869 in Bourg-en-Bresse, Ain . His grandfather was director of the Ecole Normale (Teachers College) of Bourg, and his father, Eugène Cotton was a mathematics professor at the University of Bourg, where the physicist Andre-Marie Ampere began his career. His brother Émile Cotton was a mathematician and an academic.

Aimé Cotton attended a Lycée in Bourg-en-Bresse and then the mathematical special program at the Lycée "Blaise Pascal" in Clermont-Ferrand . He entered the École normal supérieure in 1889 , and when he graduated in 1893 he won the physical science award.

As a graduate student at the physics laboratory of the École normal supérieure, he then prepared his doctoral thesis in physics. In this work he studied the relationships of polarized light with optically active substances that contain chiral molecules. In the ( absorption spectroscopy ) absorption band of these substances, he found large variations of optical rotation as a function of wavelength, which are known today as optical rotation dispersion (ORD) or the Cotton effect . He also discovered the related phenomenon of circular dichroism, the unequal absorption of right and left circularly polarized light in a material. These two phenomena were later used to determine the stereochemistry of chiral molecules in organic chemistry and biochemistry .

He was appointed maître de conférences in the scientific faculty in Toulouse in 1895 and defended his doctoral thesis in 1896 before the scientific faculty of the University of Paris . His dissertation was entitled Research on the absorption and dispersion of light by substances capable of optical rotation ( French Recherches sur l'absorption et la dispersion de la lumière par les milieux doués du pouvoir rotatoire ). In 1900 he was appointed as a lecturer (junior professor, lecturer) as a temporary substitute for Jules Violle . In 1904 he became an instructor and in 1910 a lecturer at the science faculty of the University of Paris, from where he was posted to the École normal supérieure , and stayed until 1922.

During this time he researched the interaction of light and magnetism . He first worked with Pierre-Ernest Weiss on the Zeeman effect , the splitting of spectral lines in the presence of a magnetic field . For this work, he invented a Cotton balance to precisely measure the intensity of the magnetic field. (Another Cotton balance was previously invented by William Cotton .) With Weiss he studied the magnetic splitting of the blue lines of the zinc atom and in 1907 they were able to use the ratio between the electron charge to its mass (e / m) with greater precision than the method of Joseph John Thomson .

Cotton then became interested in the Faraday effect near absorption lines and showed magnetic circular dichroism . At the same time he was working with his former classmate Henri Mouton , a biologist at the Pasteur Institute , on magnetic birefringence in colloidal solutions of magnetic particles. In 1907 they discovered the Cotton-Mouton effect , an intense magnetically induced birefringence with an optical axis parallel to the magnetic field lines.

In 1913 he married Eugénie Feytis, also a physicist. They had three children. During the Second World War , he and Pierre Weiss developed the Cotton-Weiss system, with which one could detect enemy artillery.

In 1914 he was in charge of Georges Bruhat's dissertation on circular dichroism and optical rotational dispersion. In 1917 he helped to found the Institut d'optique théorique et appliquée (Institute for Theoretical and Practical Optics), today the École supérieure d'optique . In 1914 he proposed the construction of a large electromagnet that could generate strong magnetic fields. Work on the magnet finally began in 1924 at the Service des recherches et inventions in Bellevue, later the Laboratoire du magnétisme in Meudon-Bellevue , which was ultimately named Laboratoire Aimé Cotton in his honor . Magnetic fields up to 7 Tesla were generated.

In 1919 he became chairman of the Physics Committee of the Direction des Inventions intéressant la défense nationale (directorate for inventions that are important for national defense). In 1920 he was nominated as professor for the new chair in theoretical physics and astrophysics in the Faculty of Science at the University of Paris. In 1922 he followed Gabriel Lippmann to the chair for general physics and at the same time he became director of physical research at the faculty. In 1923 he was elected to the French Academy of Sciences and in 1938 he became its president. He retired in 1941 and was replaced by Jean Cabannes as professor and laboratory director, although he retained the management of the magneto-optical laboratory in Bellevue. Also in 1941 he was captured by the German occupiers and spent a month and a half in Fresnes prison . He was later awarded the Rosette de la résistance (Rosette of Resistance). He died on April 16, 1951.

His former magnetic field laboratory has been affiliated with the Paris-South University as Laboratoire Aimé Cotton since 1967 .

swell

1. ↑ HH Willard, LL Merritt, JA Dean and FA Settle: Instrumental Methods of Analysis. van Nostrand, 6th edition, 1981, p. 415
2. ↑ A. Cotton: Absorption inégale des rayons circulaires droit et gauche dans certains corps actifs . In: Comptes Rendus hebdomadaires des Séances de l'Académie des Sciences Paris . tape 120 , 1895, pp. 989-991 .
3. ^ A. Cotton: Dispersion rotatoire anomale des corps absorbants . In: Comptes Rendus hebdomadaires des Séances de l'Académie des Sciences Paris . tape 120 , 1895, pp. 1044-1046 .
4. ^ A. Cotton: Recherches sur l´absorption et la dispersion de la lumière par les milieux doués du pouvoir rotatoire. In: Ann. Chim. Phys. tape 8 , 1896, pp. 347-432 .
5. ^ History of the Laboratoire Aimé Cotton, French

Web links

• Bibliography by some physicists of the 20th century (in French), Center d'initiation à l'Enseignement Supérieur (CIES), Lyon