Optics InfoBase is the Optical Society's online library for flagship journals, partnered and copublished journals, and recent proceedings from OSA conferences.

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.

We present a detailed theoretical study of the dielectric and magnetic response of composites containing elongated conducting inclusions—sticks. These composites are widely used as engineering materials. They can be also considered as a model to describe many processes occurring in nature, e.g., dielectric enhancement in grain-saturated porous rocks. An approach is proposed that is based on the idea of a scale-dependent local dielectric constant. We develop an effective-medium approximation and derive an equation to calculate an effective dielectric constant of the composites in the quasistatic case and for the high frequency when there is a strong skin effect in the conducting sticks. Our theory predicts very large values of the effective dielectric constant in a wide range of the stick concentration. We find that the dielectric constant can exhibit various dispersive behaviors. It can have relaxation behavior, power-law scaling behavior, or resonance dependence on the frequency. The resonance dependence occurs when the skin effect is strong and wavelength is comparable to the stick length. Then the real part of the dielectric constant has negative values in some frequency ranges. The possibility of a wave localization is discussed in that case. We consider effective magnetic properties of the conducting stick composites. We propose that the composites with nonmagnetic components will have a giant paramagnetic response as a result of a collective interaction of the sticks with an external magnetic field. © 1996 The American Physical Society.

Optical properties of metal nanowires and nanowire composite materials are studied. An incident electromagnetic wave can effectively couple to the propagating surface plasmon polariton (SPP) modes in metal nanowires resulting in very large local fields. The excited SPP modes depend on the structure of nanowires and their orientation with respect to incident radiation. A nanowire percolation composite is shown to have a broadband spectrum of localized plasmon modes. We also show that a composite of nanowires arranged into parallel pairs can act as a left-handed material with the effective magnetic permeability and dielectric permittivity both negative in the visible and near-infrared spectral ranges.

Surface-enhanced optical nonlinearities are studied in a semicontinuous film consisting of metal granules randomly distributed on an insulating substrate. The local fields are very inhomogeneous in such films and consist of strongly localized sharp peaks. In peaks (“hot” spots), the local fields exceed the applied field by several orders of magnitudes resulting in giant enhancements of the optical nonlinearities. Because of such a pattern for the local field distributions, the nonlinear signals are mostly generated from small nanometer-size areas. The corresponding spatial distributions for the generated fields form, in turn, a set of very sharp peaks on a homogeneous, on average, semicontinuous film. It is shown that the spatial positions of the localized hot spots at the fundamental and generated frequencies are located, in general, in different parts of a film. The local enhancements in the hot spots exceed the average enhancement by several orders of magnitude. The predicted giant local enhancements open fascinating possibilities in nonlinear spectroscopy of single molecules on a semicontinuous metal film. A number of surface-enhanced optical nonlinearities are studied, namely, those that are responsible for the Kerr-effect, four-wave mixing, second-, and third-harmonic generation. The enhancement for nonlinear optical processes is shown to strongly increase toward the long-wavelength part of the spectrum. Spatial distributions of the local fields are calculated in our broad-scale numerical simulations. A scaling theory for the high-order field moments is developed. It predicts that the moments of the local fields are very large and independent of the frequency in a wide spectral range. The theory predicts anomalous field fluctuations and giant enhancements for the nonlinear optical processes, from the visible to the far-infrared spectral range.