Physics Department - Chiral Exceptional Lines in the Visible Regime for Nanoscale Sensing

Abstract
This talk presents our observation of chiral exceptional lines (ELs) in the visible regime and their application to nanoscale sensing. Using a simple photonic crystal platform, we demonstrate how scattering matrices naturally provide the three-dimensional parameter space needed to host these topological features without complex structural engineering.
Our experimental approach combines Fourier-space optics with Mueller matrix spectroscopy, revealing characteristic features including self-intersecting Riemann surfaces, phase vortices, and polarization half-vortices. We'll explore how the square-root eigenvalue behavior near ELs enhances sensitivity for detecting structural variations as small as ~2 nm compared to conventional resonance-based approaches.
I'll also present our recent extension of this platform to saline concentration detection, demonstrating how ELs in scattering matrices enable versatile sensing applications across different measurement domains. This work establishes a practical connection between non-Hermitian physics and nanophotonic sensing in the visible range.