1. M. M. Sushchik, V. M. Fortus, and G. I. Freidman, Izv. VUZ. Radiofiz.,13, No. 5, 631 (1970).
2. N. Bloembergen, Nonlinear Optics [Russian translation] Mir, Moscow (1966); S. A. Akhmanov and R. V. Khokhlov. Problems of Nonlinear Optics [in Russian], VINITI, Moscow (1964).
3. A. A. Andronov, A. A. Vitt, and S. É. Khaikin, Theory of Oscillations [in Russian], Fizmatgiz, Moscow (1969).