Norman F. Ramsey Jr.
1915–2011, Washington, D.C., USA, Wayland, Massachusetts, USA
American physicist awarded half of the 1989 Nobel Prize in Physics for the separated-oscillatory-fields method that underlies the cesium atomic clock.
Born in Washington, D.C., Ramsey studied at Cambridge and Columbia, earning his PhD in 1940 under Isidor Rabi in molecular-beam magnetic resonance. After wartime work on radar and the Manhattan Project, he joined Harvard in 1947 and spent his career there. In 1949–1950 he invented the separated-oscillatory-fields technique — interrogating atoms with two spatially separated microwave pulses instead of one long one — which multiplied the precision of atomic transitions and became the operating principle of today's cesium clocks defining the SI second. With Daniel Kleppner he also developed the hydrogen maser, and he was the founding head of physics at Brookhaven National Laboratory.
Nobel-winning work
Ramsey's Nobel work concerns precision spectroscopy. In his 1949–1950 'molecular beam resonance method with separated oscillating fields', an atomic beam passes through two short rf regions separated by a drift space; the interference of the two excitations produces fringes whose linewidth is set by the flight time between the regions rather than the time inside each one — an atom interferometer in time.
This trick sharpened resonance lines by orders of magnitude, enabling hyperfine-structure and shielding measurements and, above all, the cesium-beam atomic clocks (1967 SI second definition) and the hydrogen maser developed with Kleppner in 1960.
Workplaces: Harvard University, Los Alamos National Laboratory
United States