1. Pekar,S.I.: Zh. Eksperim. i Teor. Fiz. 33, 1022 (1957); 34, 1176 (1958).
2. Hopfield,J.J., Thomas,D.G.: Phys. Rev. 132, 561 (1963).
3. Agarwal,G.S., Pattanayak,D.N., Wolf,E.: Phys. Rev. Letters 27, 1022 (1971); — Opt. Commun. 4, 255, 260 (1971).
4. Maradudin,A.A., Mills,D.L.: Taormina Research Conf. on the Structure of Matter, (1972).
5. Sein,J.J.: Ph. D. thesis, New York University (1969).