This paper discusses various aspects of a solvable quantum model introduced
by Friedrichs and Lee in field theory. Its mathematical properties are pre
sented, and its role in the early discussion of renormalizability is review
ed. It is finally stressed that the model has been of great utility in quan
tum optics, and the renown Jaynes-Cummings model is identified as its speci
al case. As an illustration it is demonstrated how the Scully-Lamb quantum
theory of the laser can be derived from the mathematics of this model. (C)
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