1. A. I. Akhiezer and I. A. Akhiezer, Electromagnetism and Electromagnetic Waves (Vysshaya Shkola, Moscow, 1985).
2. M. B. Vinogradova, O. V. Rudenko, and A. P. Sukhorukov, The Theory of Waves (Nauka, Moscow, 1979).
3. N. G. Basov, R. V. Ambartsumyan, et al., Dokl. Akad. Nauk SSSR 165, 58 (1965) [Sov. Phys. Dokl. 10, 1039 (1966)].
4. P. G. Kryukov and V. S. Letokhov, Usp. Fiz. Nauk 99, 169 (1969) [Sov. Phys. Usp. 12, 641 (1970)].
5. D. V. Vasil’ev, M. R. Vitol’, Yu. N. Gorshenkov, et al., Radio Engineering Circuits and Signals (Radio i Svyaz’, Moscow, 1982).