1. T. Baer and I. D. Abella, Phys. Rev. A 16, 2093 (1977).
2. I. Popov, I. Bikbov, I. Yevseyev, and V. Samartsev, Zh. Prikl. Spektrosk. 52, 794 (1990).
3. N. N. Rubtsova, V. N. Ishchenko, E. B. Khvorostov, et al., Phys. Rev. A 70, 023403 (2004).
4. I. S. Bikbov, I. I. Popov, V. V. Samartsev, and I. V. Yevseyev, Laser Phys. 5(3), 580 (1995).
5. A. V. Yevseyev, I. V. Yevseyev, and V. M. Ermachenko, Opt. Spektrosk. 50, 77 (1981) [Opt. Spectrosc. 50, 40 (1981)].