The Carrier Dynamics of Chiral Gold Nanoparticles.

Chiral plasmonic nanoparticles exhibit strong, tailorable chiral response in the visible spectrum, making them ideal platforms for studying light-matter interactions. Here, we investigated the ultrafast carrier dynamics in chiral gold nanoparticles under linearly and circularly polarized light. Through femtosecond transient absorption spectroscopy, we investigate the plasmon resonance broadening and quantitatively determine the electron-phonon coupling constant. We then decode the chiral-selective carrier dynamics using circularly polarized excitation. A key finding is that strong spin-orbit coupling induces transition selectivity, leading to a ∼17% enhancement in the transient absorption signal for the left circularly polarized (LCP) pump-LCP probe configuration over the right circularly polarized (RCP) pump-RCP probe configuration at 750 nm. This work provides critical insights to the polarization-controlled behavior of chiral nanomaterials, paving the way for optimization in next-generation chiral photonic and spintronic devices.