1. M. S. Lipsett and M. W. P. Strandberg, Appl. Opt., 1, 343 (1962).
2. L. D. Landau and E. M. Lifshits, Theory of Elasticity [in Russian], Nauka, Moscow (1965).
3. B. I. Stepanov (editor), Methods of Laser Design [in Russian], Vol. 1, Nauka i Tekhnika, Minsk (1966).
4. G. Nye, Physical Properties of Crystals [Russian translation], IL, Moscow (1960).