1. F. M. Johnson, J. A. Duardo: Laser Focus No. 11, 31 (1967)
2. W. L. Smith: Appl. Opt. 6, 1798 (1977)
3. R. Danelyus, A. Piskarskas, V. Sirutkaitis, A. Stabinis, Ya. Yasevichyute: Parametric Generators of Light and Pico-second Spectroscopy (Mokslas, Vilnius 1983) [In Russian]
4. F. Zernike: J. Opt. Soc. Am. 54, 1215 (1964)
5. G. C. Ghosh, G. C. Bhar: IEEE J. QE-18, 143 (1982)