Comparison of finite-difference time-domain simulations and experiments on the optical properties of gold nanoparticle arrays on gold film

We present experimental and simulated results of far-field reflection spectroscopy and two-photon luminescence microscopy of arrays of gold nanoparticles on gold film. These arrays are intended as a simplified model system compared to random arrangements of gold particles on gold film, which show huge surface enhancements for, e. g., Raman scattering of adsorbed molecules, related to the enhanced optical near-fields. By a detailed comparison of the experimental results to the finite-difference time-domain simulations (without free fitting parameters), we can identify the modes responsible for the enhancement in intensity on the investigated substrates. The qualitative and quantitative validity of the theoretical approach is addressed and we discuss the origin of the observed differences between theory and experiment as well as possible routes to overcome them.