1. Bakumenko, V. M. and Antipenko, A. P.: 1972,Radio Eng. Electronic Phys. 17, 262 (Russian original 1971).
2. Connes, P.: 1964,Quantum Electronics and Coherent Light, Varenna Summer School, p. 207 (Acad. Press).
3. Cummins, H. Z. and Swinney, H. L.: 1970,Progress in Optics, Vol. VIII, 135.
4. De Graauw, Th., Nieuwenhuyzen,. H., Van de Stadt, H., and Goebel, H.: 1975, to be publ. inOptics Communications.
5. Forrester, A. Th., Gudmundsen, A., and Johnson, P. O.: 1955,Phys. Rev. 99, 1691.