Near-field optical studies of local photomodification in nanostructured materials.

Fractal aggregates of silver nanoparticles are studied experimentally using atomic force microscopy and photon scanning tunnelling microscopy. Large changes in the near-field optical response of fractal aggregates are observed after the irradiation of samples with nanosecond laser pulses. The threshold energy density for photomodification using a 532 nm laser is measured to be 9 mJ cm(-2). It is shown that photomodification-induced changes in the local optical response can be two orders of magnitude larger than changes in far-field absorption.

Shearing interferometer based on second-harmonic generation and a novel technique of n(2) direct measurements.

We present a new wave-front sensitive interferometry technique (called dispersion shearing interferometry) for the measurement of both the sign and the magnitude of n(2). The interference pattern is produced by two laterally shifted second harmonics of the laser source. Only the fundamental wave passes through the nonlinear sample, which is placed before the interferometer. We demonstrate this technique on an aggregated colloidal silver solution using a YAG:Nd laser and KTiOPO(4) frequency doublers.