Polarization Manifestations of Structured Light in Coherently Absorbing and Symmetry-broken Media

Roy, Sauvik (2025) Polarization Manifestations of Structured Light in Coherently Absorbing and Symmetry-broken Media. PhD thesis, Indian Institute of Science Education and Research Kolkata.

Text (PhD thesis of Sauvik Roy (19RS022)) 19RS022.pdf - Submitted Version Restricted to Repository staff only Download (15MB)

Abstract

This thesis investigates the interplay of critical coupling, coherent perfect absorption (CPA), and spin–orbit interactions (SOI) in structured light fields and symmetry-broken optical systems. We first extend CPA theory to realistic beam configurations, analyzing how Gaussian and Laguerre–Gaussian beams with distinct polarization and orbital angular momentum interact with multilayer absorbers. The study shows that complete absorption is fundamentally limited in planar structures, with the transmitted and reflected beams exhibiting polarization mixing, strong distortions, and transverse shifts tied to spin–orbit coupling. These insights suggest novel routes for beam shaping and highlight the potential of CPA in advanced photonic platforms, including metasurfaces, nonlinear media, and two-dimensional materials. In parallel, we explore SOI in tightly focused beams interacting with tilted stratified media, combining theoretical modeling, simulations, and experiments. By systematically varying the refractive index contrast and tilt angle, we reveal mechanisms for enhancing spin-to-transverse-spin conversion and optimizing Belinfante spin momentum. The breaking of electromagnetic symmetry between electric and magnetic field contributions further enriches the picture. Strikingly, experiments with birefringent particles in optical tweezers uncover helicity-dependent precession and gyroscopic motion, offering an optical analogue to spin dynamics in external magnetic fields. Together, these results bridge fundamental physics and practical implementations, providing a versatile framework for controll

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