1. G. Guterlein, S. A. Kazantsev, A. V. Loginov, and I. I. Tupitsyn, Opt. Spektrosk. 90, 533 (2001) [Opt. Spectrosc. 90, 467 (2001)].
2. A. V. Loginov and I. I. Tupitsyn, Opt. Spektrosk. 91, 8 (2001) [Opt. Spectrosc. 91, 3 (2001)].
3. Go. Baśar, Gu. Baśar, and G.-H. Guthoehrlein, in Proceedings of 32nd Conference of the European Group for Atomic Spectroscopy, Ed. by Z. Rudzikas (Vilnius, 2000), p. 145.
4. S. Kröger and A. Bouzed, Eur. Phys. J. (2003) (in press).
5. G. Olsson and A. Rosen, Phys. Scr. 26, 168 (1982).