Engineering spasers: models,designs, and applications
thesisposted on 27.02.2017 by Rupasinghe, Chanaka Suranjith
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The spaser nanolaser, which is the nanoplasmonic counterpart of the laser, enables the generation and amplification of coherent surface plasmons (SPs) by means of stimulated emission. Spaser opens up a new era of devices which overcome the speed barriers of electronics and miniaturizing barriers of optics. This research is mainly focused on engineering spaser devices, particulary the guidelines for design optimization, new designs with improved characteristics, and potential applications. First, a general quantum mechanical model is developed considering the degeneracy of localized SP modes supported by a resonator. Density matrix analysis of this system helps to derive an expression for SP generation rate and identify the tunable parameters for design optimization. The developed model is then applied to optimize a simple spaser design, in which a metal nanosphere is resonantly coupled to a quantum dot, by altering their material and geometrical parameters. Next, alternative spaser materials are considered. Although not commonly used in spaser designs, graphene possesses much better plasmonic properties compared to gold or silver and carbon nanotubes (CNTs) display excellent photoluminescence properties. Therefore, a new all-carbon spaser design is proposed where a square shaped graphene nanoflake (GNF) resonator powered by a CNT gain element offering the advantages of tunability, robustness, flexibility, and thermal stability. This design is also analyzed employing the general model to determine the different material and geometric parameters of GNF and CNT influencing the spaser operation. Based on these results, clear spaser design guidelines such as identifying the crucial tuning parameters, fabricating the resonator, choosing the appropriate gain medium and pumping mechanism, and relative placement of the components are also sought. Finally, some new applications of spaser nanolasers are proposed and a spaser powered cancer therapy is discussed in detail. In this setup, a large number of tiny nanolasers penetrate tumors to thermally ablate malignant cancer cells. Hence, this research as a whole contributes towards engineering the spaser and catalyzing the process of its practical use and commercialization.