Aimé Cotton

Aimé Auguste Cotton (9 October 1869 – 16 April 1951) was a French physicist known for his studies of the interaction of light with chiral molecules. In the absorption bands of these molecules, he discovered large values of optical rotatory dispersion (ORD), or variation of optical rotation as a function of wavelength (Cotton effect), as well as circular dichroism or differences of absorption between left and right circularly polarized light.

Aimé Cotton was born in Bourg-en-Bresse, Ain on 9 October 1869. His grandfather was director of the École normale (teachers' college) of Bourg, and his father, Eugène Cotton, was a mathematics professor at the college of Bourg, the institution where physicist André-Marie Ampère began his career. His brother Émile Cotton was a mathematician and academician.

Aimé Cotton attended a lycée (high school) in Bourg and then the special mathematics program at the Lycée Blaise Pascal in Clermont-Ferrand. He entered the École normale supérieure in 1889, and won the physical sciences prize on graduating in 1893.

As a graduate student at the physics laboratory of the École normale supérieure, he then prepared his doctoral thesis in physical sciences. In this thesis he studied the interactions of polarized light with optically active substances containing chiral molecules. In absorption bands of these substances, he found large variations of optical rotation as a function of wavelength, now known as optical rotatory dispersion (ORD) or as the Cotton effect. He also discovered the related phenomenon of circular dichroism, or unequal absorption of left and right circularly polarized light. These two phenomena were later used to determine the stereochemistries of chiral molecules in organic chemistry and in biochemistry.

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