1. H. Haken, Synergetics, an Introduction, Springer-Verlag, Berlin 1977 and references quoted therein.
2. H. Haken, Laser Theory, Hanbuch der Physik XXV/2c, Springer-Verlag, Berlin 1970
3. M. Sargent III, M.O. Scully and W.E. Lamb, Laser Physics, Addison-Wesley, New York 1974
4. R. Graham and H. Haken, Z. Physik 237, 31 (1970)
5. M.O. Scully and V. Degiorgio, Phys.Rev. A 2, 1170 (1970)