1. See, for example. Y.R.Shen: Prog. Quant. Elect.4, 1 (1975);
2. J.H.Marburger: Prog. Quant. Elect.4, 35 (1975).
3. O.Svelto: Prog. in OpticsXII, 1 (1974);
4. S.A. Akhmanov, R.V. Khokhlov, A.P. Sukhorukov: InLaser Handbook, ed. by F.T. Arrechi and E.O. Schulz-Dubois (North-Holland Publishing Co. Amsterdam 1972), p. 1151
5. V.N. Lugovoi, A.M. Prokhorov: Zh. Eksp. Teor. Fiz. Pis'ma7, 153 (1968) [Translation: JETP Lett.7, 117 (1968)];