1. V. A. Kizel and V. I. Burkov, Gyrotropy of the crystals, (Science, Moscow, 1980), p. 15 (in Russian).
2. I. A. Iliev, T. N. Dimov, D. M. Ribarov, and I. J. Lalov, Z. f. Physic (B) 93, p. 321 (1994).
3. D. M. Ribarov, I. A. Iliev, T. N. Dimov, and I. J. Lalov, Z. f. Physic (B) 94, p. 65 (1994).
4. I. A. Iliev, T. N. Dimov, D. M. Ribarov, and I. J. Lalov, Z. f. Physic (B) 95, p. 126 (1995).
5. A.H. Silbershtein, S.J. Kazitzina, and L.E. Solovev, Optics and Spectroscopy 41, p. 513 (1976), (in Russian).