Investigation of the Propagation of Light in Spheroidal Core-Shell Nanoparticles with Passive and Active Dielectric Cores
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Date
2024-05
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Addis Ababa University
Abstract
Nonlinear optics (NLO) is the study of the interaction of intense laser light with matter. In the last few years, a great deal of progress has been made in our comprehension of nonlinear polarization mechanisms and how they relate to the structural properties of materials. In our work, we studied the effects of depolarization factor (L), metal fraction (p), permittivity of the host matrix (εh) and interfacial layer on the local field enhancement factor (LFEF), induced optical bistability (IOB), and bistability domain (BD) of spheroidal core-shell nanocomposites (NCs) embedded in passive or active dielectric cores. Solving Laplace’s
equation in the quasistatic limit, we obtained expressions of the electric potentials in the various regions of the NCs. Then, by introducing L and the Drude-Sommerfeld model into these expressions, we derived the equation of LFEF in the core of the NCs and studied their IOB as well as BD, theoretically and numerically. The results show that (i) firstly, whether L, p, and/or εh vary or kept constant, the LFEF of the spheroidal core-shell NCs possesses two sets of peaks with passive dielectric core, whereas there is one set of peaks with active dielectric core. In NCs with passive dielectric core, an increase in any of these parameters resulted in a more pronounced LFEF peaks in the first set of resonances. With both passive and active dielectric cores, increasing L increases the peaks of LFEF, whereas increasing p decreases the peaks of LFEF of the same material with active dielectric core. Moreover, the highest peak of LFEF is obtained by increasing L than p or εh indicating that changing the geometry of NCs has the highest effect on the LFEF. Equally increasing εh, intensities
of LFEF of the NCs decrease, when the dielectric core is passive and increase when the dielectric core is active. (ii) Secondly, the study reveals that when L decreases, the bistable region of IOB of the NCs increases. However, when p increases at constant L and εh, the bistable region gets wider. When εh increases, the IOB region is achieved at larger values of the incident field. Also, the IOB produced was narrower in the passive dielectric core than in the active one, showing that the type of core material also influences the IOB of the NCs. Moreover, when L changes, the region of BD also changes in both types of cores,
while changing p or εh in both types of cores causes the BD to vanish or emerge. (iii) Thirdly, a system consisting of metal/dielectric spheroidal NCs with interfacial layer (I), the LFEF increased successively in the given frequency range with a single peak with an increase in thickness. Consequently, the LFEF in the passive medium is red-shifted with no appreciable change in peak magnitude as the radius (r) increases, whereas the LFEF in the active host medium increases. We also studied the possibility of LFEF increasing in passive and active dielectric host matrices as p grows. In brief, the LFEF, IOB, and BD in each core are sensitive to changes in the values of L, p, and εh. Hence, varying these parameters leads to the possibility of tuning the domains of the LFEF, IOB, and BD, which can be employed in potential applications such as optical sensing, nonlinear optics, and quantum optics.
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Keywords
Investigation, Propagation of Light, Spheroidal Core-Shell Nanoparticles, Passive and Active Dielectric Cores