Cascaded plasmon resonances for enhanced nonlinear optical response

The continued development of integrated photonic devices requires low-power, small volume all-optical modulators. The weak nonlinear optical response of conventional optical materials requires the use of high intensities and large interaction volumes in order to achieve significant light modulation, hindering the miniaturization of all-optical switches and the development of lightweight transmission optics with nonlinear optical response. These challenges may be addressed using plasmonic nanostructures due to their unique ability to confine and enhance electric fields in sub-wavelength volumes. The ultrafast nonlinear response of free electrons in such plasmonic structures and the fast thermal nonlinear optical response of metal nanoparticles, as well as the plasmon enhanced nonlinear Kerr-type response of the host material surrounding the nanostructures could allow ultrafast all-optical modulation with low modulation energy. In this thesis, we investigate the linear and nonlinear optical response of engineered effective media containing coupled metallic nanoparticles. The fundamental interactions in systems containing coupled nanoparticles with size, shape, and composition dissimilarity, are evaluated analytically and numerically, and it is demonstrated that under certain conditions the achieved field enhancement factors can exceed the single-particle result by orders of magnitude in a process called cascaded plasmon resonance. It is demonstrated that these conditions can be met in systems containing coupled nanospheres, and in systems containing non-spherical metal nanoparticles that are compatible with common top-down nanofabrication methods such as electron beam lithography and nano-imprint lithography. We show that metamaterials based on such cascaded plasmon resonance structures can produce enhanced nonlinear optical refraction and absorption compared to that of conventional plasmonic nanostructures. Finally, it is demonstrated that the thermal nonlinear optical response of metal nanoparticles can be enhanced in carefully engineered heterogeneous nanoparticle clusters, potentially enabling strong and fast thermal nonlinear optical response in system that can be produced in bulk through chemical synthesis

Capsule-Based Persian/Arabic Robust Handwritten Digit Recognition Using EM Routing

In this paper, the problem of handwritten digit recognition has been addressed. However, the underlying language is Persian/Arabic, and the system with which this task is a capsule network (CapsNet) has recently emerged as a more advanced architecture than its ancestor, namely CNN (Convolutional Neural Network). The training of the architecture is performed using the Hoda dataset, which has been provided for Persian/Arabic handwritten digits. The output of the system clearly outperforms the results achieved by its ancestors, as well as other previously presented recognition algorithms.Comment: 5 pages, 10 figures, 4th International Conference on Pattern Recognition and Image Analysis (IPRIA2019), IEE

Cascaded field enhancement in plasmon resonant dimer nanoantennas compatible with two-dimensional nanofabrication methods

Cascaded field enhancement is demonstrated in asymmetric plasmon resonant dimer nanoantennas consisting of shape-tuned ellipsoidal nanoparticles. The nanoparticles that make up the dimer have identical thickness, suggesting that the presented approach can be used to design cascaded dimer antennas compatible with standard two-dimensional top-down nanofabrication tools such as electron beam lithography and nano-imprint lithography. Cascaded excitation is achieved by modification of the in-plane particle aspect ratios in a way that keeps the resonance frequency of the individual particles fixed while significantly changing their polarizability. The achievable field enhancement is evaluated as a function of the particle volume ratio and spacing

Photothermal response enhancement in heterogeneous plasmon-resonant nanoparticle trimers

The optical response of heterogeneous plasmonic trimer structures composed of a silver nanoparticle dimer and a central gold nanoparticle is investigated analytically and numerically. The plasmon resonance of the silver dimer is controlled through near-field coupling, resulting in plasmon resonance frequency matching of the silver dimer and gold monomer. This coupling condition makes it possible to increase the energy dissipation per unit volume in the gold particle by over two orders of magnitude compared to a single-particle system. It is predicted that pulsed illumination of a trimer consisting of two 80-nm-diameter silver particles and a 10-nm-diameter central gold particle can raise the gold particle temperature by 100 K using a pump fluence as low as 20 nJ/mm(2) at a wavelength of 530 nm. This finding may have practical applications in photothermal therapy, fast thermal nonlinear optical modulation, and could enable new fundamental thermal studies at picosecond time scales

Sustainable energy technology, adoption, rebound, and resilience

While in the United States, centralized generation and distribution network are the basis of the current electric infrastructure, the recent surge in uptake of solar photovoltaic (PV) systems introduces a new avenue to decentralize this system. Furthermore, PV systems can substitute the grid electricity and increase the share of renewable energy sources. While by 2018, five states in the U.S. (California, Hawaii, Nevada Massachusetts, and Vermont) could reach 10% threshold for the share of solar sources in generating electricity, at the country level this share is still less than 3%; whereas in some other countries, such as Germany and Japan, it has already reached more than 6%. This dissertation examines the diffusion of PV systems from three perspectives, addressing three gaps in knowledge: an empirical study of the diffusion of PV systems in Georgia, a method to estimate renewable rebound effect, and a framework to quantify the resilience capacity of an electric infrastructure system with emergency electricity generators, including PV systems. Three studies present the primary contributions of this research. Study 1 examines the diffusion of PV systems in Georgia, identifies characteristics of adopters and patterns of adoption, and forecasts the future adoption of PV systems. Study 2 introduces a new approach to estimate the direct rebound effect, subsequent of a major adoption of PV systems. Study 3 presents a state-of-the-art framework that quantifies the resilience capacity of an electric infrastructure system with emergency electricity generators. The findings of the study 1 provides a benchmark for the future adoption of PV systems and highlights the impact of socio-economic and location-based factors in the diffusion of PV systems in Georgia. These findings can be used to shape a more effective policy, aiming to increase the share of PV systems, or evaluate the effectiveness of a policy. The finding of the study 2 opens a new avenue to compute the rebound effect and can support development of a policy to mitigate the renewable rebound effect in a targeted region. The finding of the study 3 can help system designers to customize the design of a resilient system based on its characteristics. The introduced framework can further be used to investigate improvement of the resilience capacity in an electric infrastructure system by increasing the penetration of PV systems, or other decentralized electricity generators in a region.Ph.D

Heterogeneous plasmonic trimers for enhanced nonlinear optical absorption

A dramatic enhancement of the thermally induced nonlinear optical response in compositionally heterogeneous plasmonic trimers is reported. It is demonstrated numerically that the nonlinear absorption performance of silver nanoparticle dimers under pulsed illumination can be enhanced by more than two orders of magnitude through the addition of only 0.1 vol. % of gold in the dimer gap. The nonlinear absorption performance of the resulting Ag-Au-Ag trimer exceeds the peak performance of isolated gold nanoparticles by a factor 40. This dramatic effect is enabled by cascaded plasmon resonance, resulting in extreme field concentration in the central nanoparticle of the trimer. The observed localized heat-generation, large optical response, and a predicted response time below 1 ns make these structures promising candidates for use in nonlinear optical limiting and optical switching