1. D. M. Bloom, P. F. Liao, and N. P. Economou, Opt. Lett.,2, No. 3, 58 (1978).
2. M. V. Vasil'ev, V. G. Sidorovich, and N. S. Shlyapochnikova, Opt. Spektrosk.,54, No. 4, 663 (1983).
3. B. Ya. Zel'dovich, N. P. Pilinetskii, and V. V. Shkunov, Wavefront Reversal [in Russian], Nauka, Moscow (1985).
4. V. I. Bespalov and G. A. Pasmanik, Nonlinear Optics and Adaptive Laser Systems [in Russian], Nauka, Moscow (1985).
5. S. M. Rytov, Zh. Eksp. Teor. Fiz.,33, No. 1, 166 (1957).