1. E. V. Savchenko, Yu. I. Rybalko and I. Ya. Fugol', Pisma Zh. Eksp. Teor. Fiz.,42, No. 5, 210 (1985).
2. E. V. Savchenko, Yu. I. Rybalko and I. Ya. Fugol', Fiz. Nizk. Temp.,14, No. 4, 399 (1988).
3. F. V. Kusmartsev and E. I. Rashba, Czech. J. Phys.,B32, 54 (1982).
4. N. Schwentner, O. Dossel and H. Nahme, Laser Techniques for Extreme Ultraviolet Spectroscopy. AIP Conf. Proc. 90, New York (1982).
5. E. Gullikson, Phys. Rev. B,37, No. 13, 7904 (1988).