Second‐harmonic spectroscopy of nano‐interfaces

Abstract

Optical second-harmonic is shown to be a noninvasive, interface-sensitive probe of silicon nanocrystals. The TEM 01 spatial mode of SHG radiation from a silicon nanocrystal composite indicates there is nonlocal dipolar (quadrupolar) polarization source which is proportional to the gradient of the incoming electric field. With two orthogonally polarized laser beams, we enhanced the SHG from nanocrystals by creating wavelength-scale, forward-radiating gradient in the second-harmonic polarization. The quantitative features of two-beam SHG were also studied with a fused silica slide. We demonstrate several techniques for isolating the nano-interface signal from the (bulk-quadrupolar) substrate signal in our samples.