Sources of plasmons: Probing the excitation and steering of plasmons from quantum emitters and nano-structured metal surfaces
- Doctoral Thesis
Rights / licenseIn Copyright - Non-Commercial Use Permitted
Surface plasmon polaritons (SPPs) are propagating electromagnetic surface waves at the interface between a metal and a dielectric. These surface waves can be confined to and manipulated at length scales smaller than the classical diffraction limit for light. Consequently, optical devices based on plasmons can be built with sizes smaller than their purely photonic counterparts, and the interaction between the strongly confined electromagnetic fields of SPPs and matter can enable new device designs that are more efficient and cost-effective. To build such plasmonic devices, SPPs need to be generated and steered. In this thesis, we contribute to the ongoing search and optimization of SPP sources that can be fabricated with minimal space requirements and integrated in miniaturized plasmonic devices. First, we develop nanoscopic probes to experimentally study how light-emitting nanoparticles in the close proximity of a metal surface can excite SPPs. The nanoprobes are doped with Eu3+ ions which feature optical transitions with electric-dipole and magnetic-dipole character. A measurement of the competition between these transitions for nanoprobes placed at a well-defined distance in front of a plasmonic reflector allows for probing of the local density of optical states associated with SPPs. Our measurements show that the local plasmonic environment around light-emitting nanoparticles can be used to enhance the SPP emission rate and to steer the plasmon-emission direction through self-interference of the emitted SPPs. Our findings highlight that both the symmetry of the dipole source and the orientation of the transition dipole moment affect the SPP emission. Second, we study plasmonic lasers based on distributed-feedback cavities made from Ag and colloidal semiconductor nanoplatelets as the gain material. Nanostructuring of the Ag surface with periodic protrusions leads to the formation of plasmonic stop gaps, which are responsible for the laser feedback. We find that the stop gaps sensitively depend on the exact design of the protrusions. Simple design rules to maximize the performance of plasmonic distributed-feedback lasers are obtained through a Fourier decomposition of the height profile of the plasmonic cavity. The experimentally observed lasing modes in our optimized second-order distributed-feedback lasers are in good agreement with established coupled-wave theory but suffer from diffractive photon leakage. In contrast, we observe pure SPP output in our plasmonic lasers with first-order feedback except for weak outscattering at localized defects. Third, we investigate plasmonic surfaces with height profiles given by a discrete sum of sinusoids, each with a well-defined amplitude, phase, and reciprocal lattice vector. Our group has recently developed a simple yet powerful approach that combines thermal scanning-probe lithography and templating to fabricate such Fourier surfaces with high spatial resolution. We develop a microscopy method to probe the diffraction occurring on miniaturized Fourier surfaces in momentum space. For structures consisting of a sinusoid and its phase-shifted harmonic, the experimentally measured diffraction can be rationalized as interference and competition between different diffraction pathways opened by the individual sinusoids. Further, we demonstrate with our microscopy technique that a plasmonic surface with a height profile consisting of three superimposed sinusoids with different spatial frequencies acts as a grating coupler that excites SPPs at three colors for light incident from the surface normal. In summary, this thesis investigates different types of SPP sources with experimental model systems that allow for understanding the processes involved in the SPP generation. We develop new approaches to experimentally probe these model systems and we extract intuitive design rules that can be applied to develop improved SPP sources. Show more
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ContributorsExaminer: Norris, David J.
Examiner: Barnes, William L.
Examiner: Quidant, Romain
Examiner: Rabouw, Freddy T.
SubjectOptical materials; Nanotechnology; Surface plasmon polaritons; Plasmonics; Nanooptics; Nanostructured materials; Nanocrystals; Europium; Nanoplatelets; Distributed-feedback lasers
Organisational unit03875 - Norris, David J. / Norris, David J.
339905 - Quantum-Dot Plasmonics and Spasers (EC)
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