Experimental study of optical second-harmonic scattering from spherical nanoparticles

Optical second-harmonic (SH) generation from the surface of spherical particles of radii much smaller than the optical wavelength has been investigated experimentally. Angle- and polarization-resolved measurements from dye-coated polystyrene spheres have been obtained for radii of 55 and 85 nm. The SH signals obey general axial- and polarization-selection rules. The polarization-resolved angular patterns agree with the electromagnetic theory of SH Rayleigh scattering that describes the process in terms of locally excited quadrupolar and nonlocally excited dipolar emission. The experimental results differ significantly from those predicted for a local dipole-allowed SH scattering process.