1. W. E. Lamb, Jr., Phys. Rev. 134, 1429 (1964).
2. W. Å. Lamb, Jr., Theory of Optical Masers, in Lecture Notes on Quantum Optics and Electronics at the Summer School of Theoretical Physics at the University of Grenoble (Les Houches, 1964) Ed. by C. DeWitt, A. Blandin, and C. Cohen-Tannoudji (Gordon and Breach, New York, 1965), pp. 329–381.
3. W. R. Bennett, Jr., J. Appl. Opt. (Suppl.) 1, 24 (1962).
4. T. V. Radina, Opt. Spektrosk. 106(2), 337 (2009).