MACROSCOPIC SIZE EFFECTS IN 2ND-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 1 and 3 00 nm. The Brewster angle of incidence, pin, p-out combination of pola rizations and strong, uniform suppression of this effect by near-index matching fluid exclude trivial multiple reflections and microscopic i nterface effects. The observation can be interpreted to originate from the optical (Casimir) nonlocality stemming from the thickness-depende nt electron-electron interaction via virtual photons of the quantized electromagnetic field.