1. W. H. Steel:Progress in Optics, Vol. V, ed. by E. Wolf (North-Holland Publ. Co., Amsterdam, 1960) p. 145
2. M. Born, E. Wolf:Principles of Optics (Pergamon Press, Oxford, 1959) p. 490
3. A. Lohmann: Opt. Acta9, 1 (1962)
4. S. Nawata: Oyobutsuri33, 86 (1964), in Japanese
5. S. Nawata, T. Suzuki: Oyobutsuri33, 716 (1964), in Japanese