We discuss the phenomenon of enhanced fluorescence in the proximity of metal nanostructures addressing the question of how much fluorescence signal can be obtained from fluorophores in such altered environments. We review its applicability for the methodologies used in the life science, such as immunoassays, flow cytometry and bioimaging. Experimental and theoretical scenarios employing various metal nanostructures - such as homogeneous enhancing substrates, fluorescence-enhancing microbeads, and metal core-dielectric shell nanocomposites - are described.

We report on the fabrication of sapphire samples containing platinum nanoparticles (Pt-NPs) and platinum ions (Pt-ions) and the investigation of their third-order nonlinear (NL) optical properties. The presence of Pt-NPs was confirmed by electronic microscopy and by the linear absorption spectrum that shows a localized surface plasmon band centered at 290 nm. A sample without NPs but containing Pt-ions was also studied. The absorptive and refractive contributions to the nonlinearity were studied using the z-scan technique with 100 fs pulses at 800nm. The experiments revealed a NL refractive index, +3.8×10^-13 < n₂ < +1.3×10^-12cm²/W and NL absorption coefficient (β < 9.3 cm/GW). The results show enhancement of about five orders of magnitude with respect to the NL refractive index of sapphire.

Exploiting a giant plasmonic field enhancement in an anisotropic array of gold nanorod clusters in a polyvinyl alcohol (PVA) film, we have experimentally studied its nonlinear absorptive and refractive response. Gold nanorod cluster-PVA nanocomposites were prepared, and the uniaxial alignment was obtained by mechanically stretching the films. Using the Z-scan method and excitation with 100 fs pulses at 800 nm, intensities up to 70 GW/cm2 at 20 Hz, saturation of both nonlinear absorption and nonlinear refraction were observed. The results are discussed in light of a plasmonic effect arising from the gold nanorod clusters aligned in the stretched polymeric matrix. A polarization dependent sign reversal of the nonlinear refraction was observed, which can find applications in nanoscale photonic devices. The results are supported by finite element analysis of local electric field distribution in the arrays of gold nanorod clusters.

We observe and analyze formation, decay, and subsequent regeneration of ring-shaped clusters of (2+1)dimensional spatial solitons (filaments) in a medium with cubic-quintic (focusing-defocusing) self-interaction and strong dissipative nonlinearity. The cluster of filaments, which remains stable over ≈17.5 Rayleigh lengths, is produced by the azimuthal modulational instability from a parent ring-shaped beam with embedded vorticity l = 1. In the course of still longer propagation, the stability of the soliton cluster is lost under the action of nonlinear losses. The annular cluster is then spontaneously regenerated due to power transfer from the reservoir provided by the unsplit part of the parent vortex ring. Thus, a secondary interval of the robust propagation of the regenerated cluster is identified. The experiments use a laser beam (at wavelength 800 nm), built of pulses with temporal duration 150 fs, at the repetition rate of 1 kHz, propagating in a cell filled by liquid carbon disulfide. Numerical calculations, based on a modified nonlinear Schrödinger equation which includes the cubic-quintic refractive terms and nonlinear losses, provide results in close agreement with the experimental findings.

We report the properties of plasmons in dense planar arrays of silver single and double nanostructures with various geometries fabricated by electron beam lithography (EBL) as a function of their size and spacing. We demonstrate a strong plasmon coupling mechanism due to near-field dipolar interactions between adjacent nanostructures, which produces a major red shift of the localized surface plasmon resonance (LSPR) in silver nanoparticles and leads to strong maximum electric field enhancements in a broad spectral range. The extinction spectra and maximum electric field enhancements are theoretically modeled by using the finite element method. Our modeling revealed that strong averaged electric field enhancements of up to 60 in visible range and up to 40 in mid-infrared result from hybridization of multipolar resonances in such dense nanostructures; these are important for applications in surface enhanced spectroscopies.