Second-harmonic microscopy of single micrometer-size particles on a substrate

We report experimental observations of second-harmonic generation (SHG) from single micrometer-size polystyrene, silica, and polymethylmethacrylate spheres on flat substrates by SHG microscopy. At low input light intensities the SH signals depend quadratically on the intensity of the excitation beam, but at larger input intensities some of the SH signals increase exponentially with increasing input intensity. This exponential enhancement depends on particle size and sphere composition. We describe the experiments, and parametrize the observations.