Parity-Time Transition in non-Hermitian spin-orbit interaction Optical System

Rahaman, Saminur (2025) Parity-Time Transition in non-Hermitian spin-orbit interaction Optical System. Masters thesis, Indian Institute of Science Education and Research Kolkata.

Text (MS Dissertation of Saminur Rahaman (20MS103)) 20MS103_Thesis_file.pdf - Submitted Version Restricted to Repository staff only Download (1MB)

Abstract

We present a unified theoretical study of transverse optical beam shifts in plasmonic grating interfaces, revealing a striking non-Hermitian behavior in the Imbert–Fedorov (IF) displacement under partial reflection. By analyzing the eigenspectrum of the corresponding shift matrix (Artmann operator), we identify a transition in its eigenvalues—from real to imaginary—that closely mirrors the parity-time (PT) symmetry breaking observed in non- Hermitian Hamiltonians. This PT-like phase transition is absent in the Goos–Hänchen shift under the same conditions, highlighting a unique feature of the transverse shift. We trace the origin of this transition to the momentum-domain evolution of the beam’s polarization: partial reflection induces an inhomogeneous polarization modulation across the angular spectrum, which fundamentally alters the Hermiticity of the IF shift operator. Further, we show that this mechanism extends to any polarization anisotropy element when rendered inhomogeneous in momentum space, establishing partial reflection of a Gaussian beam as a minimal yet powerful prototype for exploring non-Hermitian spin-orbit photonics. Our results open new avenues for harnessing PT-symmetry concepts in entirely passive optical systems.

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