Experimental observation of localized optical excitations in random metal-dielectric films

Localization of optical excitations within subwavelength areas of a random metal-dielectric film is observed using near-field scanning optical microsc opy. 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" spot s, where the fields are much greater than the applied held. The local near- field spectra consisting of strong resonance peaks are detected and shown t o depend markedly on the sample site probed. The observed spectral peaks co rrespond to localized modes of random metal-dielectric films. [S0031-9007(9 9)09244-3].