Localization of optical excitations within subwavelength areas of a random metal-dielectric film is observed using near-field scanning optical microscopy. This effect is attributed to Anderson localization of surface plasmon modes in a semicontinuous metal film. The localized modes are seen as giant fluctuations of local electric fields spatially concentrated in “hot” spots, where the fields are much greater than the applied field. The local near-field spectra consisting of strong resonance peaks are detected and shown to depend markedly on the sample site probed. The observed spectral peaks correspond to localized modes of random metal-dielectric films.

• Received 28 January 1999

DOI:https://doi.org/10.1103/PhysRevLett.82.4520