Super Radiant Narrowing in Fluorescence Radiation of Inverted Populations

The effect of resonance reabsorption of fluorescent radiation on the spectral distribution has been considered as early as 1913 by Laudenburg and Reivhe [1]. Schein [2] and Zemansky [3] recognized that the reabsorption causes a broadening of the light emitted by resonance lamps. In this note we report an experimental and theoretical study of the complementary effect, i.e., of resonance radiation originating in a system in which the population of the upper level of the resonance transition is made to exceed that of the lower one (inverted population system).