1. Hamal K., Kvapil J., Škoda V.: in Proc. CLEO 1987, Baltimore (USA), p. 60, 75.
2. Belousova I.M., Grenishin A.S., Kiselyov V.M., Kudimova M.A., Slominskii Yu.L., Tolmachyov A.I.: Kvantovaya elektron. (Moscow) 9 (1982) 2313.
3. Farcy J.A., Beaupere D., de Witte O.: C. R. Acad. Sci. France 284 (1977) 467.
4. Batashev S.P., Galpern M.G., Katulin V.A., Lebediev O.L., Lukyanets E.A., Mekhryakova N.G., Mizin V.M., Nosach V.Yu., Petrov A.L., Petukhov V.A.: Kvantovaya elektron. (Moscow) 6 (1979) 2652.