Second harmonic generation from a collection of nanoparticles

In this paper we discuss the SH radiation produced by a composite film made up of nanosized spherical centrosymmetric homogeneous particles. Although each individual sphere is unable to radiate in the forward direction when illuminated by a plane wave, our results show that for a thin composite film illuminated by a focused gaussian linearly polarized beam the radiation pattern presents two narrow lobes displaced along the polarization direction by a small angle of the order of the diffraction-induced angular divergence of the linear far field. The SH radiation produced by a non-homogeneous film, on the other hand presents non-trivial patterns which depend on the fundamental frequency, the waist of the illuminating beam, the sharpness of the edge, the density profile and both the incoming and outgoing polarizations. We hope that these results can be extended to develop characterization techniques for composite films based on surface SHG or SFG. (C) 2003 WILEY-VCH Veflag GmbH & Co. KGaA, Weinheim.