1. V. I. Talanov, Paper presented at the Third All-Union Symp. on Nonlinear Optics, Erevan (1967).
2. A. P. Veduta and B. P. Kirsanov, Zh. Eksp. Teor. Fiz.,56, No. 4, 1175 (1969).
3. F. W. Perkins and E. I. Valeo, Phys. Rev. Lett.,32, No. 22, 1934 (1974).
4. R. W. Hellwarth, JOSA,67, No. 1, 1 (1977).
5. A. Yariv, IEEE,QE-14, No. 9, 650 (1978).