1. W. H. Louisell, A. Yariv, and A. E. Siegman, Phys. Rev., 124, 1646 (1961).
2. W. H. Louisell, Coupled Mode and Parametric Electronics, Wiley, New York (1960).
3. R. J. Glauber, Phys. Rev., 131, 2766 (1963).
4. B. R. Mollow and R. J. Glauber, Phys. Rev., 160, 1076 (1967).
5. J. V. Schwinger, in: L. C. Biedenharn and H. Van Dam (Eds.), Quantum Theory of Angular Momentum, Academic Press, New York (1965), p. 229.