Macroscopic Size Effects in Second Harmonic Generation from Si(111) Coated by Thin Oxide Films: The Role of Optical Casimir Nonlocality

Optical second harmonic generation from Si(111)-SiO2 interface shows a strong nonmonotonic dependence on the oxide thickness between 2 and 300 nm. The Brewster angle of incidence, p-in, p-out combination of polarizations and strong, uniform suppression of this effect by near-index matching fluid exclude trivial multiple reflections and microscopic interface effects. The observation can be interpreted to originate from the optical (Casimir) nonlocality stemming from the thickness-dependent electron-electron interaction via virtual photons of the quantized electromagnetic field. copyright 1996 The American Physical Society