1. For review articles on this subject, see L. Mandel, in Progress in Optics, Vol. XIII, ed. by E. Wolf (North-Holland Publishing Co., Amsterdam, 1976) Ch. II; P. W. Milori, Phys. Reports 25, 1 (1976).
2. R. J. Glauber, Phys. Rev. Letters 10, 84 (1963).
3. L. J. Schiff, Quantum Mechanics ( McGraw-Hill Book Co., New York, 1949 ) p. 240.
4. See, for instance, H. Haken, Handbuch der Phpsik, Vol. XXV/2c ( Springer Verlag, Berlin, 1970 ).
5. E. T. Jaynes, in Coherence and Quantum Optics, ed. by L. Mandel and E. Wolf ( Plenum Press, New York, 1973 ) p. 35.