Surface-enhanced optical third-harmonic generation in Ag island films
  Surface-enhanced optical third-harmonic generation (THG) is observed in silver island films. The THG intensity from Ag nanoparticles is enhanced by more than two orders of magnitude with respect to the THG intensity from a smooth and homogeneous silver surface. This enhancement is attributed to local plasmon excitation and resonance of the local field at the third-harmonic wavelength. The diffuse and depolarized component of the enhanced THG is associated with the third-order hyper-Rayleigh scattering in a 2-D random array of silver nanoparticles. 
E.M. Kim, S.S. Elovikov, T.V. Murzina, A.A. Nikulin, O.A. Aktsipetrov,   M.A. Bader and G. Marowsky