1. A. M. Polubotko, Preprint No. 882 (Ioffe Physical Technical Institute, 1984).
2. A. M. Tsyganenko and A. A. Polubotko, Opt. Spektrosk. 59(4), 881 (1985) [Opt. Spectrosc. 59 (4), 530 (1985)].
3. A. M. Polubotko, Preprint No. 1151 (Ioffe Physical Technical Institute, 1987).
4. A. M. Polubotko, Phys. Lett. A 146, 81 (1990).
5. A. M. Polubotko, Phys. Lett. A 276, 197 (2000).