Rydberg state masers

The threshold condition for collective emission (superradiance) or maser action (gain in the medium exceeding the losses) is much lower for Rydberg atoms than it is for the same number density of atoms in low n states. To obtain an order of magnitude estimate for the point at which collective fects occur we estimate the amplitude of the electric dipole field E radiated by an atom at a distance corresponding to a neighbouring atom. That is, if we let L represent a linear dimension in the sample which contains N atoms,... 

With the use of a resonant cavity the threshold for collective emission is lower by the magnitude of the cavity finesse. Using a cavity finesse of a 100 or so Rydberg maser action on sodium has been observed. In this case the field ionisation signal was used to monitor the population as a function of time for the states 27S, 26P and 25P corresponding to transitions An = 1 at X = 1 470 mm and An = 2... 

Fig. 9.73 Schematic experimental setup for the one-atom maser with resonance cavity and state-selective detection of the Rydberg atoms [1294]...

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