Investigation of spin-orbit interactions of light in epsilon-near-zero materials

Jana, Aloke (2023) Investigation of spin-orbit interactions of light in epsilon-near-zero materials. Masters thesis, Indian Institute of Science Education and Research Kolkata.

Text (MS dissertation of Aloke Jana (18MS197)) Thesis_18MS197.pdf - Submitted Version Restricted to Repository staff only Download (14MB)

Abstract

Nowadays, spin-orbit interactions (SOI) of light have become a rapidly growing re- search field in the domain of nanophotonics since it provides a tool to control and ma- nipulate the spatial degrees of freedom acting on its polarization state. Similarly, epsilon- near-zero (ENZ) materials draw a considerable amount of attention due to its ability to in- teract with the electromagnetic field in a very unconventional way. Integrating these two, we have proposed that SOI effects can be enhanced when a light beam passes through a subwavelength thick, isotropic and homogeneous ENZ slab due to the large asymmet- ric response of two mutually orthogonal polarized electromagnetic fields. In this regard, to study the SOI effects at any planer interfaces, we have made a generalized frame- work using the angular spectrum method, and the framework itself can encompass any type of inhomogeneous medium, including ENZ or stratified media. We indeed have observed the enhancement of both spin and orbital angular momentum dependent shifts of the light beam (spin-Hall and orbital-Hall effects respectively). Moreover, we have ex- perimentally demonstrated paraxial spin-to-vortex conversion in a subwavelength thick ENZ slab. Furthermore, the effect of symmetry breaking has been taken into account to obtain very interesting vortex-splitting results due to the generation of nonzero trans- verse angular momentum by pumping the Indium-Tin-Oxide (ITO) slab with asymmetric Bessel-Gaussian beam. These findings, along with the large nonlinearity of the ENZ ma- terials, already give a hint that ENZ materials can be used as a potential platform for investigating the SOI effects in nonlinear regimes. The second part of the thesis deals with the generation of higher order intrinsic or- bital angular momentum (OAM) carrying vortex beams and its application in polarime- try. In this regard, we have corrected the wavefront aberration induced by SLM and all the other optical elements using the iterative phase retrieval Gerchberg-Saxton (GS) algorithm. We have successfully generated and detected higher order vortex beam up to l = 350. Subsequently, we have proposed and experimentally demonstrated a novel optical sensor based on vortex beams for measuring the polarization rotation of opti- cally active molecules. The proposed detection scheme is based on the rotation of the intensity ’petal pattern’ itself, obtained from the co-axial superposition of the two op- positely twisted vortex beams. We, indeed, have measured the specific rotation of the glucose solution as well as its direction of rotation. Moreover, our method can easily be extended to measure very small displacements in nanometer length scale with high pre- cision. Therefore, the proposed vortex sensor has potential sensing applications such as micro-vibration, surface distortions and motion of microbes.

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