1. H. Hirayama and W. Terashima, Proc. SPIE 9585, 958504 (2015).
2. A. R. Calawa, J. O. Dimmock, T. C. Harman, and I. Melngailis, Phys. Rev. Lett. 23, 7 (1969).
3. G. S. Baronov, D. K. Bronnikov, I. I. Zasavitskii, S. M. Karavaev, A. S. Razumov, and A. P. Shotov, in Proceedings of the 19th All-Union Workshop on Spectroscopy, Tomsk, Russia, 1983, Part IV, p. 25.
4. I. I. Zasavitskii, A. V. Matveenko, B. N. Matsonashvili, and V. T. Trofimov, Sov. Phys. Semicond. 20, 135 (1986).
5. I. I. Zasavitskii, Tr. FIAN 224, 3 (1993).