Léon Nicolas Brillouin (French:[leɔ̃nikɔlabʁijwɛ̃]; August 7, 1889 – October 4, 1969) was aFrenchphysicist. He made contributions toquantum mechanics,radio wave propagation in the atmosphere,solid-state physics, andinformation theory.
Brillouin was born inSèvres, near Paris, France. His father,Marcel Brillouin, grandfather,Éleuthère Mascart, and great-grandfather,Charles Briot, were physicists as well.
From 1908 to 1912, Brillouin studied physics at theÉcole Normale Supérieure, in Paris. From 1911 he studied under Jean Perrin until he left for theLudwig Maximilian University of Munich (LMU), in 1912. At LMU, he studied theoretical physics withArnold Sommerfeld. Just a few months before Brillouin's arrival at LMU,Max von Laue had conducted his experiment showingX-ray diffraction in a crystal lattice. In 1913, he went back to France to study at theUniversity of Paris and it was in this year thatNiels Bohr submitted his first paper on theBohr model of the hydrogen atom.[1] From 1914 until 1919, during World War I, he served in the military, developing thevalve amplifier with G. A. Beauvais.[2] At the conclusion of the war, he returned to the University of Paris to continue his studies withPaul Langevin, and was awarded hisDocteur ès science in 1920.[3] Brillouin's thesis jury was composed of Langevin,Marie Curie, andJean Perrin and his thesis topic was on thequantum theory of solids. In his thesis, he proposed an equation of state based on the atomic vibrations (phonons) that propagate through it. He also studied the propagation of monochromatic light waves and their interaction withacoustic waves, i.e., scattering of light with a frequency change, which became known asBrillouin scattering.[4][5]
After receipt of his doctorate, Brillouin became the scientific secretary of the reorganizedJournal de Physique et le Radium. In 1932, he became associate director of the physics laboratories at theCollège de France. In 1926,Gregor Wentzel,[6]Hendrik Kramers,[7] and Brillouin[8] independently developed what is known as theWentzel–Kramers–Brillouin approximation, also known as theWKB method,classical approach, andphase integral method.[9] In 1928, after theInstitut Henri Poincaré was established, he was appointed as professor to the Chair for Theoretical Physics. During his work on the propagation of electron waves in a crystal lattice, he introduced the concept ofBrillouin zones in 1930. Quantum mechanical perturbations techniques by Brillouin and byEugene Wigner resulted in what is known as the Brillouin–Wigner formula.[4][5][10]
Since Brillouin's study with Sommerfeld, he was interested and did pioneering work in the diffraction of electromagnetic radiation in a dispersive media.[11] As a specialist in radio wave propagation, Brillouin was appointed director general of the French state-run agency,Radiodiffusion Nationale about a month beforewar with Germany, August 1939. In May 1940, upon thecollapse of France, as part of the government, he retired toVichy. Six months later, he resigned and went to the United States.[4][5]
Until 1942, Brillouin was a visiting professor at theUniversity of Wisconsin–Madison, and then he was a professor atBrown University, inProvidence, Rhode Island, until 1943. For the next two years, he was a research scientist with theNational Defense Research Committee atColumbia University, working in the field ofradar. From 1947 to 1949, he was professor of applied mathematics atHarvard University. During the period 1952 to 1954, he was withIBM Corporation inPoughkeepsie,New York, as well as a staff member of theIBM Watson Laboratory at Columbia University. In 1954, he became an adjunct professor at Columbia University. From 1957, he was founding editor ofInformation and Control, and served as one of its three, later four editors until 1966.[12] He lived in New York City until he died in 1969.[4][5] His wife Marcelle died in 1986.
Brillouin was a founder of modernsolid state physics for which he discovered, among other things,Brillouin zones. He appliedinformation theory to physics and the design of computers and coined the concept ofnegentropy to demonstrate the similarity between entropy and information.[4][5]
Brillouin offered a solution to the problem ofMaxwell's demon. In his book,Relativity Reexamined, he called for a "painful and complete re-appraisal" ofrelativity theory which "is now absolutely necessary."
Léon Brillouin married Stéphanie "Stéfa" Prussak in 1912 in Paris, France.[13] Stéfa Prussak was born 17 December 1890 in Lodz, Poland and was a painter and avid collector of art.[14] They had one daughter, Isabelle "Bella" Brillouin, who later married Gilbert Boris. Stéfa died in Paris on March 17, 1966 after an illness. Léon Brillouin remarried a few years later to a friend of his first wife, Marcelle van Praag (born Marcelle Esther Lioni), and were together until his death on October 4, 1969[15][note 1]. His widow Marcelle (known as Madame Brillouin), and his daughter from his first marriage, Bella, managed his estate and gifted his archival papers and papers related to his father and grandfather to the AIP Niels Bohr Library & Archives in 1970.[15]
Media related toLéon Brillouin at Wikimedia Commons
