1. Yu. I. Ostrovskii, G. F. Parchevskii, and N. P. Penkin, Opt. ispektr.,1, 821, 1956.
2. E. Hinnov, H. Kohn. JOSA,47, 156, 1957.
3. B. V. L'vov, IFZh,2, 44, 1959; IFZh,2, 56, 1959.
4. B. L. Vallee and A. F. Bartholomay, Analyt. Chem.,28, 1753, 1956.
5. E. Badarau, M. Giurgea, Gh. Giurgea, and A. Trutia. Proc. Colloquium Spectroscopicum Internat., vol. I. London, Pergamon Press., 441, 1957.