OPTICAL 2ND-HARMONIC GENERATION OF METAL-ISLAND FILMS

In metal-island films consisting of nanometer particles on a transparent substrate irradiated light fields can be locally enhanced by electron-plasma resonances. Therefore, nonlinear optical processes should be enhanced dramatically. However, second-order nonlinear processes as second-harmonic generation occuring in the surface are strongly reduced by the centrosymmetric shape of the metal particles. It is found that this surface-specific contribution to second-harmonic generation is less enhanced, as is expected from the field enhancement. The ''bulk'' contribution, at smooth metal surfaces known to be much weaker than the contribution from the ''real surface'', is strongly enhanced by the plasma resonances without symmetry restrictions and becomes comparably important.