Mueller matrix spectroscopic studies on plasmonic and complex biomaterials

Chandel, Shubham (2019) Mueller matrix spectroscopic studies on plasmonic and complex biomaterials. PhD thesis, Indian Institute of Science Education and Research Kolkata.

Text (Phd thesis of Shubham Chandel (14RS013)) 14RS013.pdf - Submitted Version Restricted to Repository staff only Download (4MB)

Abstract

Plasmonics has appealed a lot of consideration in past few decades owing to its numerous potential application and possible fundamental studies. In the noble metal nanoparticles/nanostructures, the optical properties at sub-wavelength scale are ruled by the collective oscillations of the free or the conduction electrons oscillating in resonance with the incoming electromagnetic field. These oscillations are acknowledged as Surface Plasmon Resonance (SPR). The most important quality of SPR is the high localization and strongly enhanced electromagnetic fields. The SPR has been distinguished in two forms depending on the occurrence of the resonance, localized at nanoparticle/nanostructures or propagating at metal-dielectric interfaces. The intrinsic sensitivity towards local environment and distinctive spectral characteristics had encouraged ample research work especially for potential applications. Some of the important applications could be named like Sensing (chemical, bio-molecular), data storage, contrast enhancement, drug delivery, optical information processing and many more. Plasmon resonances are explored not only because of the potential applications but also owing to its potential in probing various fundamental effects linked to the interaction of light with plasmonic nanostructures, like Spin Orbit Interaction, quantum spin hall effect, Plasmonic Aharonov-Bohm effect, coupled plasmons and plasmonic Fano resonances etc. These studies are not limited to one field rather expanded to research areas including atomic to quantum to condensed matter systems. In this context, the study of interaction of polarized light with matter is much more interesting and useful especially, at sub-wavelength scales. Polarization being a crucial player in the light matter (read plasmonic nanostructures) had created the impulse to gather the polarization properties of these interactions (say scattering) in the fundamental plasmonic effects mentioned above. And not only the effects but the polarization information becomes crucial in optimization of experimental parameters for the potential applications mentioned. Although, some preliminary work in the context of „plasmon polarimetry‟ has already been made, but those works are usually limited to measurements of co- and/or the crossed polarization. Such limitations are based on partial gathering of polarization information and thus have received only moderate success. In addition to that, these partial studies have been mostly semi-empirical and semi-quantitative on the underlying complex nature of the polarized light-matter interactions. This explains clearly that the quantitative polarimetric approaches and studies are still the underdog and they are yet to realize their full potential. Recently, Mueller matrix measurements from large metallic array of nanoparticles have been reported using commercially available system, though it has been executed in the reflection domain. Even the studies were semi-quantitative using the Fresnel coefficients. Though no such system/study is available that can do quantitative polarimetry from a series of nanostructures like individual to complex Plasmonic nanoparticle/nanostructure. No such studies have been reported to have complete polarization recorded exclusively from the scattered signal from the individual to complex nanostructures, nor the analysis of the same using the recorded scattered polarization parameters. Such studies/recordings (Mueller matrix) have the potential to provide deep understanding of the underlying fundamental plasmonic effects and also providing an edge in the applications too. One of the outstanding challenges in experimental Mueller matrix polarimetry (in biomedical regime), is to develop strategy / experimental systems that can enable full Mueller matrix measurements simultaneously at broad wavelength range from variety of systems (e.g highly turbid tissues, nanoparticles, nanostructures etc). Development of such strategy and methods may facilitate near simultaneous quantitative spectroscopic polarimetry and imaging. Moreover, such capability may also lead to extension of conventional Mueller matrix measurements (which are typically done for elastic scattering, reflection/refraction only) to include inelastic scattering spectroscopy, such as Raman spectroscopy and Fluorescence spectroscopy. Development of such novel spectroscopic Mueller matrix measurement methods may thus add an extra dimension in conventional optical spectroscopy, enabling a novel approach for probing subtle features associated with molecular organization, structures through spectroscopic polarimetry parameters (which are otherwise hidden in conventional polarization blind spectroscopy). A simple general one line version will be, “This thesis explores the scattering of polarized light from various Plasmonic and complex biological systems”.

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