1. H. M. Gibbs, G. Khitrova, and N. Peyghambarian, Nonlinear Photonics (Springer, Berlin, 1990).
2. S. I. Wawilov and W. L. Lewschin, Z. Phys. 35, 932 (1926).
3. S. I. Vavilov, Microstructure of Light (Academy of Sciences of the USSR, Moscow, 1950), p. 70 [in Russian].
4. D. N. Klyshko, Physical Bases of Quantum Electronics (Nauka, Moscow, 1986) [in Russian].
5. S. H. Park, M. P. Casey, and J. Falk, J. Appl. Phys. 73, 8041 (1993).