Alfred Kastler
1902–1984, Guebwiller, Alsace, German Empire (now France), Bandol, France
French physicist who invented optical pumping, the use of light to control the internal states of atoms, founding modern optical methods in atomic physics.
After teaching in lycées and assisting Jean Bricard in Bordeaux, Kastler turned to optical spectroscopy, measuring Raman scattering and fluorescence. At the École Normale Supérieure in Paris from 1941 he built the Laboratoire de physique de l'ENS, where with Jean Brossel he realized double resonance and, in 1950, optical pumping — techniques that later underpinned atomic clocks and laser cooling.
Nobel-winning work
Kastler's 1966 Nobel Prize honored 'the discovery and development of optical methods for studying Hertzian resonances in atoms'. His optical pumping scheme used polarized resonance light to empty certain Zeeman sublevels and accumulate atoms in oriented or aligned states.
Monitoring the repopulation by radiofrequency transitions then revealed hyperfine structures and relaxation processes with unprecedented sensitivity. The method revolutionized atomic spectroscopy and became the ancestor of today's atomic clocks, magnetometers, and laser-cooling techniques.
Workplaces: École Normale Supérieure, Paris, University of Bordeaux
France