Random Metal-dielectric Films Research Articles

Performance of Random Metal-Dielectric Film on Optical Signal Transmissions

The transmission performances of a random metal-dielectric film composed of silver metal and spherical fused silica balls were experimentally investigated for intensity- and frequency-modulated optical signals. The film was formed on the facet of a laser diode, and intensity-modulated optical signals emitted from the laser diode were successfully transmitted through it. Frequency-modulation optical signals were successfully detected by using an optical heterodyne technique. These results indicate that this random metal-dielectric film is well suited for use as a waveguide for optical signal transmission.

Local field distribution in random metal–dielectric films; theory and experiment

The local field properties of metal–dielectric films are investigated in terms of the probability distribution function (PDF). For metal coverage p, close to the percolation threshold we obtain a wide, lognormal PDF which for low metal concentrations gradually transforms into a scaling, power-law distribution function. Strong enhancement of the local fields in a broad spectral range is verified by an exact numerical procedure. In experimental studies, metal–dielectric films were synthesized by a pulsed laser deposition technique, and their optical properties were investigated using near-field optical microscopy. The experimentally and numerically obtained probability functions are found to be in good agreement.

Plasmon localization and local field distribution in metal-dielectric films.

An exact and very efficient numerical method for calculating the effective conductivity and local-field distributions in random R-L-C networks is developed. Using this method, the local-field properties of random metal-dielectric films are investigated in a wide spectral range and for a variety of metal concentrations p. It is shown that for metal concentrations close to the percolation threshold (p=p(c)) and frequencies close to the resonance, the local-field intensity is characterized by a non-Gaussian, exponentially broad distribution. For low and high metal concentrations a scaling region is formed that is due to the increasing number of noninteracting dipoles. The local electric fields are studied in terms of characteristic length parameters. The roles of both localized and extended eigenmodes in Kirchhoff's Hamiltonian are investigated.

Near-field optical studies of semicontinuous metal films

Local field distributions in random metal-dielectric films near a percolation threshold are experimentally studied using scanning near-field optical microscopy (SNOM). The surface-plasmon oscillations in such percolation films are localized in small nanometer-scale areas, ``hot spots,'' where the local fields are much larger than the field of an incident electromagnetic wave. The spatial positions of the hot spots vary with the wavelength and polarization of the incident beam. Local near-field spectroscopy of the hot spots is performed using our SNOM. It is shown that the resonance quality-factor of hot spots increases from the visible to the infrared. Giant local optical activity associated with chiral plasmon modes has been obtained. The hot spot's large local fields may result in local, frequency and spatially selective photomodification of percolation films.

PERCOLATION AND FRACTAL COMPOSITES: OPTICAL STUDIES

Local field distributions are studied in random metal–dielectric films near percolation (percolation films) and fractal aggregates of colloidal particles. For both systems, it is shown that optical excitations are localized in small nanometer-scale areas, "hot spots," where the local fields are much larger than the field of an incident electromagnetic wave. The large local fields result in giant enhancement of various optical phenomena. The surface-enhanced white-light generation and second-harmonic generation have been obtained in percolation films. For fractal aggregates of silver particles, a giant effect of local optical activity has been observed. The effect is due to surface-plasmon excitations localized on chiral-active particle configurations in fractals.

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 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.