1. Handbook of Physical Quantities, Ed. by I. S. Grigoriev and E. Z. Meilikhov (Énergoizdat, Moscow, 1991; CRC, Boca Raton, 1997).
2. K. Watanabe, in Advances in Geophysics, Ed. by H. E. Landsberg and J. van Mieghem (Academic, New York, 1958), Vol. 5, p. 153.
3. R. V. Babcock, I. Liberman, and W. D. Partlow, IEEE J. Quantum Electron. 12, 29 (1976).
4. V. M. Borisov, G. G. Gladush, and Yu. Yu. Stepanov, Kvantovaya Élektron. 4, 809 (1977).
5. I. I. Gromova and A. V. Yakovleva, Izv. Akad. Nauk SSSR, Ser. Fiz. 27, 1097 (1963).