Study of local photomodification of nanomaterials using near-field optics

Thin films of randomly distributed silver nanoparticles are studied experimentally using photon scanning tunneling microscopy and theoretically using real-space renormalization group method. The studies reveal large variations of local optical intensity at sub-wavelength scales. In addition, irradiation of the film by nanosecond laser pulses is observed to yield substantial changes in the local optical response. The threshold for the photomodification is less than 10 mJ/cm 2 . It is believed that particles within some areas of nanometer scales are restructured during nanosecond laser irradiation. The geometric changes in turn result in modification of the local optical intensity.