Jean Brossel (1918–2003)

news and views

Obituary Jean Brossel (1918–2003)

Jean Brossel passed away on 4 February population of magnetic sublevels inside 2003 in Périgueux, Dordogne, the city the ground state. of his birth. He was one of the founding In 1951, Kastler and Brossel founded a fathers of the modern French school of research group together at the Ecole quantum optics and co-founder, with Normale — what became the Laboratoire Alfred Kastler, of the Laboratoire Kastler Kastler Brossel (LKB). Their primary Brossel at the Ecole Normale Supérieure, objective was to demonstrate optical in Paris. pumping experimentally and to explore Brossel entered the Ecole Normale in the possibilities it created. Excellent 1938, completing his studies in 1945 (after students from the Ecole Normale soon a two-year interruption due to the Second joined the group (Bernard Cagnac, Jacques World War). Physics research in France Winter, Jacques Blamont and Jean-Pierre was devastated by the war, and lagged Barrat, among many others). This field behind the scientific developments in of research proved to be a treasure trove Britain and the United States. To catch of new physics. Optical pumping was up, Kastler advised Brossel to begin his demonstrated in 1952, and was followed research in the United Kingdom. Brossel by the observation of multiphoton took his advice and joined Samuel resonances, where several photons, instead Tolansky’s group in Manchester, in the of a single one, are absorbed by the atoms laboratory headed by Patrick Blackett. at the same time — Brossel provided a There he learned how to apply physical interpretation of the selection interferometry to the study of surfaces, rules for the polarization of the radio sceptical about application-driven research and to use Fabry–Perot interference frequency in terms of photon angular in universities. He argued that technical techniques for the measurement of momentum. Then, in work overseen by breakthroughs are the fruit of hyperfine structure in electronic fundamental research driven by pure transitions inside the atom. Throughout Physicist who opened scientific curiosity, and rarely of his life, Brossel acknowledged the value application-oriented programmes. A good of the expertise he acquired in Tolansky’s up new perspectives example is atomic clocks, which sprang laboratory. in quantum optics from fundamental studies in atomic LABORATOIRE KASTLER BROSSEL KASTLER LABORATOIRE On Brossel’s return from England, physics rather than from a drive to Kastler recommended that he go to the Brossel and Kastler, came coherent improve on mechanical or quartz clocks. United States to work for a PhD with radiation trapping and polarization Another example is optical pumping in Francis Bitter at the Massachusetts transfer, the general distinction between helium-3. First performed 20 years ago Institute of Technology. Bitter had just diagonal and off-diagonal elements of by King Walters and Laird Schearer in informed Kastler about exciting new ideas the density matrix (populations and the United States, optical pumping in this for Doppler-free spectroscopy (in which coherences) and the discovery of light isotope was refined at LKB, motivated by Doppler broadening of optical emission shifts. After Kastler received the Nobel the study of quantum effects in optically lines does not limit the resolution) that prize in 1966 for his work on optical pumped gases. Now optical pumping might extend radio-frequency studies of methods for studying resonances of the in helium-3 forms the basis of a tool for atomic resonances to excited states. Bitter’s atom, he often expressed his deep regret the medical imaging of lung cavities in idea turned out to be incorrect, but it that Brossel had not shared it with him. asthma patients. proved a fruitful starting point for Brossel Brossel encouraged young scientists to Jean Brossel was for many years the that later led to his invention of the pursue new directions of research in his head of the physics department at the method of ‘double resonance’: in this laboratory. This research included work Ecole Normale, to which he attracted Doppler-free method, the atoms are on atomic masers and magnetometers, brilliant and active colleagues. Teaching subjected to simultaneous irradiation parity-violation in atomic physics, cavity was always important to him, in with light and a radio-frequency field, electrodynamics and Doppler-free two- particular as a way of attacting the and resonant effects are detected by photon spectroscopy. Perhaps the best- best students to physics. But even at the measuring the polarization of the known application of optical pumping peak of his administrative responsibilities, fluorescent light emitted by the atoms is in atomic clocks, and the work done he never abandoned ‘hands-on’ work (equivalent to the angular momentum at LKB, in particular on light shifts, in the laboratory. For instance, he of the photons), instead of its frequency was crucial to their development. continued to prepare glass cells (the energy of the photon). Improvements in the optical pumping of containing atomic gases, sometimes While Brossel was finishing his thesis rubidium atoms led to the creation in 1969 with elaborate coatings to prevent wall with Bitter, Kastler followed a similar of a magnetometer that was sensitive to relaxation — an art in which no one could line of work in Paris and devised ‘optical magnetic fields at the level of 10ǁ9 gauss. match his skill. He will be remembered pumping’, by which atoms in their In 1997, Brossel’s colleague and former by his colleagues and former students lowest-energy (or ground) state acquire student Claude Cohen-Tannoudji shared with great admiration. Franck Laloë angular momentum through successive the Nobel prize for his work on ultra-cold Franck Laloë is in the Laboratoire Kastler Brossel, cycles of absorption of polarized optical atoms and laser cooling. Département de Physique de l’ENS, radiation, followed by spontaneous Although Brossel was interested in 24 rue Lhomond, 75005 Paris, France. emission. The final result is a selective the applications of his research, he was e-mail: [email protected]