Multiscale THz Polarization Activity: From Chiral Phonons to Micro- and Macrostructures

PASSCODE: TCD

Terahertz (THz) electromagnetic waves have emerged as a powerful tool for investigating physical phenomena that lie between the electronic and photonic regions. This dissertation explores multiscale polarization activity in the THz regime, utilizing THz time-domain polarimetry (THz-TDP) to investigate how THz polarization interacts with material systems from the atomic to the macroscopic scale.

First, we explore chiral phonons in nanocrystalline mercury sulfide (HgS), revealing THz circular dichroism (TCD) arising from the energy-matched interaction between THz light and the oscillation of intrinsic chiral lattices. Arranging these nanocrystals into microscale achiral pillar arrays significantly enhances TCD via collective resonance.

Next, we demonstrate coupling between chiral phonons and chiral plasmons using arrays of chiral microneedles (ARCHIMs). ARCHIMs exhibit strong intrinsic chiroptical activity through chiral plasmonic modes. Coating them with L– and D-cystine crystals induces clear handedness-dependent TCD shifts, confirming resonant coupling between chiral plasmons and phonons.

Finally, we develop THz polarization-sensitive computed tomography (PS-CT) to reconstruct three-dimensional anisotropic contrast from THz linear dichroism (TLD). Validation with aligned silver nanowires (AgNWs) reveals orientation-specific features.

This work establishes a unified framework for understanding and applying multiscale THz polarization activity, advancing chiral material characterization and polarization-sensitive THz imaging for next-generation THz photonic technologies.

CO-CHAIRS: Professor Nicholas A. Kotov & Professor Theodore B. Norris