Spin Optical Effects in Spatially Tailored Media

Das, Antariksha (2018) Spin Optical Effects in Spatially Tailored Media. Masters thesis, Indian Institute of Science Education and Research Kolkata.

PDF (MS dissertation of Antariksha Das (13MS055)) 13MS055.pdf - Submitted Version Restricted to Repository staff only Download (3MB)

Abstract

In optics, the angular momentum of light is related to the circular polarization of light waves known as spin angular momentum (SAM) or the helical/twisted phase fronts of light waves, known as orbital angular momentum (OAM). The mutual conversion and interplay between spin angular momentum (SAM) and orbital angular momentum (OAM) is known as spin-orbit interaction (SOI) phenomena in optics. These include the spin-Hall effect of light (SHEL), orbital-Hall effect of light (OHEL) etc. The origin of all SOI phenomena in optics is related to the generation of geometric phase and conversion of total angular momentum of light. The Idea is to explore the fundamental origin and important applications of the spinoptical effects due to both fundamental interests and potential nanophotonics applications. In parallel to the developments of SOI in optics, metamaterial and metasurfaces give us the opportunity to manipulate optical degrees of freedom (both SAM and OAM) in achieving better resolution and efficiency in spin-controlled shaping of light via designing the metasurfaces. Here, we describe the spin-optical effects in spiral nano-plasmonic structure. Particularly, we show the emergence of spin-specific modes due to the generation of random geometrical phase whenever the spatial inversion symmetry is violated which is obtained via creating random phase gradient structure in the spatial light modulator (SLM). In the field of spin-optics, we believe that our findings will provide a route to control light by tailoring optical degrees of freedom. We also report other variants of spin- Hall effect which is Geometric Spin Hall effect of light. This effect is independent of light-matter interactions and materials properties. Since the effect is in sub-wavelength scale, we have employed weak measurement technique to amplify and faithfully observe the geometric SHEL. A key feature of our weak measurement scheme is that both the weak perturbation (tiny geometric SHEL) and the post-selection are done simultaneously by a single optical element, namely, a linear polarizer. The dependence of the weak value of the geometric SHEL on the pre and the post-selection of polarization states in both linear and elliptical basis were also investigated in details.

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