|Ph.D Student||Berkovitch Nikolai|
|Subject||Localized Plasmons in the Near Infrared Regime|
|Department||Department of Electrical and Computer Engineering||Supervisor||PROF. Meir Orenstein|
|Full Thesis text|
The fundamental physical properties of the interaction between light and nanometer-size metal nanostructures are of great interest recently. It is well known, that near the plasmon resonance frequency, light strongly interacts with metal particles, even when the particles’ size is much smaller than the wavelength of the excitation field. Understanding the surface plasmon phenomena in metal nanostructures facilitates a variety of interesting and important tools in controlling light-matter interactions: guiding light in nano-scale, tailoring the transmission and absorption via proper design of the nanostructures-based metamaterials, sensing of single molecules, enhancing the fields on nano-scale with variety of nonlinear effects and much more. While most of the research on localized plasmon resonances is focused on excitation of plasmons in the visible part of the spectrum (the native plasmon resonance frequency of particles made of noble metals), many important applications in biology and communications require plasmon resonances in the Near Infrared part of spectrum.
The thesis deals with theoretical and experimental investigation of the conditions that are required in order to excite the localized plasmon resonance in metallic nanoparticles, and it presents rigorous methods to shift localized plasmon resonances from visible to the Near Infrared regime. We showed the dependence of the resonance on geometrical aspect ratio of the particles and emphasized the importance of concave geometry for large tunability of the plasmon resonance frequency. Then the coupling between adjacent nanoparticles and its dependence on polarization of the excitation field was investigated. Behavior of the nanoparticles in capacitive and conductive coupling regimes was shown, and for the conductive regime we found rules that determine the location of the resonance of a coupled structure and its tunability. For the capacitive coupling regime we have investigated the rules of combining several plasmonic nanoparticles within the unit cell of the plasmonic metamaterials and we have shown method of eliminating the dark modes in coupled structures; such method can be used for building broadband plasmonic metamaterials. We also have shown different applications of the localized plasmon resonance such as enhancement of two-photon and spontaneous emission from semiconductors, improvement in the performance of the organic solar cell, and embedding nano-antenna within Bragg grating structure. Finally, collocation of up to two different resonances in nanoparticles (e.g. dipole and quadrupole) at the same wavelength was shown theoretically using evolutionary algorithm.