Second-harmonic generation fromC60thin films at 1.064 μm

We have performed in situ optical second-harmonic-generation measurements using 1.064-μm wavelength laser pulses on ${\mathrm{C}}_{60}$ during film growth. We present a complete theoretical description of second-harmonic generation from a thin-film system in terms of surface and bulk contributions as well as local and nonlocal contributions to the optical nonlinearities. The experimental results can be well described in terms of only nonlocal contributions to both surface and bulk nonlinear susceptibilities. We suggest that in our case the second-harmonic-generation process is resonantly enhanced by the ${\mathit{h}}_{\mathit{u}\mathrm{-}}$ ${\mathit{t}}_{1\mathit{u}}$ and ${\mathit{h}}_{\mathit{u}\mathrm{-}}$ ${\mathit{t}}_{1\mathit{g}}$ transitions in ${\mathrm{C}}_{60}$ and that electric-dipole and electric-quadrupole radiations in the output field are comparable in strength.