Alfred Kastler (1902-1984) was a French physicist known for his significant contributions to the field of laser physics and atomic spectroscopy. He was awarded the Nobel Prize in Physics in 1966 for his work on the optical methods for studying Hertzian resonances in atoms, which laid the groundwork for various laser technologies. Kastler's research focused on the interaction between light and matter, and he developed techniques for manipulating and analyzing atomic energy levels using light.
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Alfred Kastler developed optical pumping, using selective absorption and emission of light to redistribute populations among atomic Zeeman sublevels. Angular momentum selection rules make some transitions accessible and others forbidden, so repeated illumination can produce a strongly unequal population. A subsequent magnetic resonance changes that distribution and therefore the detected light. Optical preparation and optical readout connect a weak radio frequency excitation with a sensitive optical signal.[ref]
Optical methods for studying Hertzian resonances by Alfred Kastler. Nobel lecture: population redistribution, optical pumping and optical detection of resonance
A physicist.[ref]
https://www.lkb.fr/en/laboratory/presentation/history/alfred-kastler-2/. Independent professional profile
Portrait of Alfred Kastler
. Unknown photographer; scan from Problemy, April 1967, p. 221. Public domain per Commons PD-Poland: qualifying Polish publication without clear copyright notice before 23 May 1994; File also states U.S. non-restoration conditions. Source usage terms, via Wikimedia Commons. Source.