Polarization Spectroscopy of Plasmonic Metamaterials

Ray, Subir Kumar (2019) Polarization Spectroscopy of Plasmonic Metamaterials. PhD thesis, Indian Institute of Science Education and Research Kolkata.

Text (PhD thesis of Subir Kumar Ray (13RS007)) 13RS007.pdf - Submitted Version Restricted to Repository staff only Download (6MB)

Abstract

This thesis reports the complete studies of the intriguing spectroscopic polarization response of engineered nanomaterials whose optical properties are not found in naturally occurring materials, popularly known as metamaterials. Metamaterials are made of assemblies of ‘meta-atoms’ to form the composite materials for example metal nanostructures. Such kind of metal nanostructures has enabled to discover the general laws governing the dynamics of light, e.g., refraction, reflection, and diffraction. Most of the time, the coupling between light and material structure are very weak and they act like separate entities. However, strong coupling of light and artificial material structure has shown several interesting effects such as extra-ordinary optical transmission, coherent perfect absorption/Scattering (CPA/CPS), electromagnetically induced transparency(EIT), Super and subluminal propagation of wave packets, negative index of refraction , etc. Therefore, the average electromagnetic response of the metamaterials can be controllably manipulate using polarization degrees of freedom of light from precisely engineered meta-atoms (unit block of metamaterials). Study of complete polarization transformation due to the interaction of polarized light with plasmonic metamaterials thus could be useful to probe number of interesting and intricate polarization effects as well as could lead to potential spin (polarization) optical metadevices. In order to study the complete polarization response of plasmonic metamaterials, the background, basic concepts, and motivation for studying light-matter interaction in a plasmonic metamaterial system and its controlled manipulation at a nanometer length scale is addressed in the very beginning of this thesis. Specifically, different types of surface plasmon resonance phenomena including localized surface plasmon resonance (LSPR) and propagating surface plasmon resonance (PSPR); Fano resonance and its distinctness from conventional Lorentzian resonance and its potential application in the nano-optical domain are discussed. A current state-of-the-art of plasmonic Fano resonances in the nano-optical system is also included. This thesis also includes the basic concepts of various optical polarization formalism, mathematical framework of polarization algebra, namely, Jones algebra, stokes-Mueller algebra, which are used in this thesis in the context of tailoring Fano resonance. It also includes the experimental challenges for Mueller matrix measurement in the spectral domain from nanostructures in free space and how these difficulties are taken care of using a dark field Microscopy. Additionally, a fluorescence Mueller matrix measurement strategy in free space is included to extend the study of similar kind of anisotropic nanomaterials. We have chosen an interesting nanostructure metasurface consist of waveguided plasmonic crystal (WPC) for polarization controlled manipulation of plasmonic Fano resonance. Numerical simulations of various Waveguided nanoplasmonic crystals using FEM-based commercial package COMSOL Multiphysics are performed to optimize the geometrical structure parameters in order to keep the spectral asymmetry within our experimental spectroscopic window. Simulation results include extinction spectra ranging from a simple plasmonic system like nano-rod, nano-disk, nano-ellipse to 1D waveguided grating, 2D waveguided disk array, and 2D ellipse array. Based on simulated extinction spectra, performed fabrication details of chosen waveguided plasmonic crystals are presented. Then we have demonstrated a novel Mueller matrix model that can control or modulate Fano resonance by tuning some experimentally accessible parameters, are highly desirable for realistic application. Polarization properties of light are employed to tailored Fano spectral line shape in a waveguided plasmonic crystal for applications involving control and manipulation of electromagnetic waves at the nanoscale. Therefore, we have presented a simple approach using Mueller matrix formalism for controlling the Fano interference effect and engineering the resulting asymmetric spectral line shape in the anisotropic optical system. The approach is founded on a generalized model of anisotropic Fano resonance, which relates the spectral asymmetry to physically meaningful and experimentally accessible parameters of interference, namely the Fano phase shift and the relative amplitudes of the interfering modes. The differences in these parameters between orthogonal linear polarizations in an anisotropic system are exploited to desirably tune the Fano spectral asymmetry using pre- and post-selection of optimized polarization states. The concept is demonstrated on waveguided plasmonic crystals using Mueller matrix-based polarization analysis. The approach enabled tailoring of several exotic regimes of Fano resonance in a single device, including the complete reversal of the spectral asymmetry line shape. Further, we have explored another possible way to tailor asymmetric spectral line shape of Fano resonance using geometric phase of light in a spatially tailored waveguided plasmonic crystal metasurface. We have experimentally established a direct link between the spectral asymmetry parameter “q” and a physically realizable phase factor of interference between a continuum and a discrete mode that leads to Fano resonance. Using a specially designed metamaterial, namely waveguided plasmonic crystal with a spatially varying orientation axis of plasmonic grating, we demonstrate control on the spectral asymmetry of the Fano resonance through changes in the geometric phase of polarized light. In this scenario, the changes in the geometric phase for input left, and right circular polarized light arises due to varying orientation angle of the grating axis. The systematic changes in the geometric phase and the resulting q-parameter of Fano resonance is interpreted by an appropriate theoretical model connecting the two physical entities. It consists of theoretical formalism, numerical simulations, and experimental results, finally conclude with a discussion. In the next phase of our research work, a real-life application based device construction using Fano resonance is demonstrated in this thesis. We have demonstrated that the highly poisonous arsenite As(III) contamination in groundwater could be detected using spectral Fano resonance in a waveguided plasmonic crystal with remarkable sensitivity. The approached is based on the tiny change in the local dielectric environment, which leads to change in Fano spectral asymmetry parameter ‘q.’ In this context fabrication of 1D waveguided plasmonic grating were performed guided by extinction spectra from simulations using COMSOL, presented in this thesis. Experimentally measured high fluorescence intensity from arsenic bonded FPICT molecules and binding stoichiometric measurement (Jobs plot), which confirms the selective binding of As(III) compared to other metal ions. Based on the optimized polarization state of light, scattering from a one dimensional waveguided plasmonic crystal spectral Fano asymmetry parameter (q) shows systematic changes for different concentrations of arsenic with incident TM-x polarized light. We have demonstrated a simple yet elegant approach for arsenic sensing and quantifying the concentration of arsenic present in a medium using waveguided plasmonic crystals. Based on this approach, we have proposed a simple low-cost waveguided plasmonic metadevices which can rapidly detect and quantify the amount of Arsenite present in a medium for example, water using optimized polarization state of light. We have then extended your research of spectroscopic Mueller Matrix studies towards fluorescence Mueller matrix recording from a Norbomin based polymer matrix E. Full polarization spectroscopic fluorescence Mueller Matrix studies employed for extraction and quantification of the molecular orientational order of both the ground (excitation) and excited (emission) state anisotropies via a set of newly defined parameters, namely the fluorescence diattenuation (differential excitation of fluorescence between two orthogonal polarizations) and fluorescence polarizance (differential emission of fluorescence between two orthogonal linear polarization). For this purpose we have selected wavelength λ= 405 nm beams and excited the matrix E which is close to the absorption band maxima at λ= 399 nm. The fluorescence is found to be highly anisotropic both during excitation and emission. In this situation, the Norbomin based polymer matrix E likely undergoes HOMO-1 to LUMO+27 transition with negligible contribution from HOMO to LUMO+14 and HOMO-1 to LUMO+6 transitions. We have also shown higher anisotropy during emission of fluorescence signal from the matrix E implying to have more organized emission of fluorescence at the excited state of the molecule manifesting as the fluorescence polarizance. The information contained in the recorded fluorescence Mueller matrix of Matrix E enabled a useful way to control the spectral intensity of emission using pre and post-selection of polarization states. The observation was on the assumption for the longer lifetime of the excited dipolar orientation attributed to matrix compactness. Finally, the main findings of the thesis and future prospect of research in the domain of nanoplasmonics for developing polarization controlled optical devices and the potential of the optical polarimetry in fluorescence studies has been summarized. The research findings presented in this thesis thus bring new insight on the controlled manipulations of scattered light in the domain of nano-plasmonics, specifically in Fano resonance and indicate considerable promise for developing polarization (spin) based photonic devices for potential applications in real life.

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