Ultrafast nonlinear plasmonics

Abstract

Metal nanostructures can enhance the optical signals by orders of magnitude due to surface plasmon resonance. This field enhancement of the plasmonic nanostructures has led to optical detection and light manipulation beyond the free space diffraction limit. However, the significant enhancement of optical signals of the nanostructures has not been fully understood. In order to examine field-enhanced phenomena, this dissertation studies a variety of plasmonic nanostructures using two nonlinear optical processes, multiphoton-absorption-induced luminescence (MAIL) and metal-enhanced multiphoton absorption polymerization (MEMAP).

Nonlinear absorption of near-infrared light can lead to luminescence of metal nanostructures. This luminescence can be observed at localized areas of the nanostructures because of localized surface plasmon resonance and the “lightning rod” nanoantenna effect. In the presence of a prepolymer resin, luminescence generated from the nanostructures can induce polymerization by exciting a photoinitiator. The strong correlation between MAIL and MEMAP is demonstrated by using different excitation wavelengths and different types of prepolymer resins.

While localized surface plasmon resonance plays a pivotal role in field-enhanced optical phenomena observed at local areas of gold nanoparticles, nanowires, and nanoplates, surface plasmon propagation is essential to understanding of the nonlinear optical properties in silver nanowires. As silver nanowires can support surface plasmon propagation for many microns, excitation of NIR light at one end of the nanowire can induce luminescence at the other end of the nanowire. This broadband luminescence can excite a photoinitiator, inducing polymerization. The luminescence-induced polymerization in remote positions can be used to assemble nanostructures.

Nonlinear luminescence and its correlation to polymerization are also studied using carbon nanostructures. While metal nanostructures exhibit plasmonic field enhancement, carbon nanotubes have strong Coulomb interactions between excited electrons and holes, which results in luminescent emission. Additionally, the high density of electron states of carbon nanotubes can increase the probability of the recombination of the excited electron and hole, which in turn induce luminescence. The luminescence emission and photopolymerization are studied using different kinds of carbon nanostructures.