1. B. K. Sevast'yanov, Kh. S. Bagdasarov, L. B. Pasternak et al., Pis'ma Zh. Eksp. Teor. Fiz.,17, No. 2, 69?71 (1973).
2. M. M. Zakharko, Ya. M. Zakharko, and V. A. Sen'kin, Ukr. Fiz. Zh.,15, No. 10, 1970?1973 (1970).
3. I. N. Duglas, Phys. Status Solidi A,9, No. 2, 635?641 (1972).
4. V. M. Markushev, V. I. Tsaryuk, and V. F. Zolin, Opt. Spektrosk.,58, No. 3, 583?588 (1985).
5. G. Burns, E. A. Geiss, M. I. Jenkins, and M. I. Nathan, Phys. Rev. A,139, No. 5, 1687?1693 (1965).