... Rasing2 1 2 1 Department of Physics, Moscow State University, Moscow 119899, Russia Research Institute for Materials, University of Nijmegen, Toernooiveld 1, NL 6525 ED Nijmegen, The Netherlands (Received 27 March 1996) Optical second harmonic generation from Si(111)-SiO 2 interface shows a strong nonmonotonic dependence on the oxide thickness between 2 and 300 nm. ... Electronic address: aktsip@astra.phys.msu.su [1] H. B. G. Casimir and D. Polder, Phys. Rev. 73, 360 (1948). ... Phys. Usp. ...