1. Luisell W. H.: Quantum Statistical Properties of Radiation. J. Wiley & Sons, New York, 1973.
2. Abragam A.: Principles of Nuclear Magnetism. Oxford University Press, London and New York, 1961.
3. Allen L., Eberly J. H.: Optical Resonance and Two Level Atoms. J. Wiley & Sons, New York, 1975.
4. Zubarev D. N.:in Results of Sciences, ser. Contemporary Problems of Mathematics15. VINITI, Moscow, 1980 (in Russian).
5. Hioe F. T., Yoo H.-I., Eberly J. H.:in Coupled Nonlinear Oscillators (eds. J. Chandra and A. C. Scott). North-Holland Publ. Co., Amsterdam, 1983.