Spin-optical effects in micro and nanoscale optical systems

Singh, Ankit Kumar (2020) Spin-optical effects in micro and nanoscale optical systems. PhD thesis, Indian Institute of Science Education and Research Kolkata.

Text (PhD thesis of Ankit Kumar Singh (13IP027)) 13IP027.pdf - Submitted Version Restricted to Repository staff only Download (8MB)

Abstract

The spin/polarization of a light beam is associated with the direction of the oscillation of electromagnetic waves in space. The oscillation of an electromagnetic wave controls its interaction with matter (or scatterer). We have utilized the fact to control the longitudinal momentum distribution of light in the scattering from the Fano resonant system and the transverse momentum distribution of light in the scattering from a disordered anisotropic system as well as a single spherical particle. Specifically, a model is proposed for the anisotropic Fano resonant systems based on the experimentally accessible parameters: the relative amplitude and the Fano phase shift between the two spectrally interfering modes. The model is experimentally verified using Mueller matrix-based approach on specially fabricated waveguided plasmonic crystals. A special regime of the model is also proposed and experimentally demonstrated, which enables faithful amplification of small anisotropy in the resonance parameters (resonance frequency and width of resonance) when the polarization of the incident light is weakly coupled to the spectral response of a Fano resonant scatterer. Subsequently, the spin selectivity of the transverse momentum distribution is demonstrated in a spin asymmetric disordered inhomogeneous anisotropic medium (prepared using a spatial light modulator) and even a simple nonbirefringent spherical scatterer. Specifically, perfect synchrony between the spatial distribution of geometric and dynamical phases of light is presented to observe the extreme spin-asymmetric random scattering modes in the transverse momentum space. Additionally, we theoretically demonstrate the spin selectivity of transverse momentum distribution even from a single isotropic spherical Mie particle for incident focused light. We also studied the illusive spin-independent transverse spin angular momentum of light and the role of input frequency of light, and the strength of focusing on the transverse momentum and the spin angular momentum is studied. The demonstrated controlled tuning of the momentum distribution with spin/ polarization of light could open up novel routes for various tunable nano-optical devices and spectroscopic applications.

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