Reversible Ultrafast Chiroptical Responses in Planar Plasmonic Nano-Oligomer.

(Ultracompact chiral plasmonic nanostructures with unique chiral light-matter interactions are vital for future photonic technologies. However, previous studies are limited to reporting their steady-state performance, presenting a fundamental obstacle to the development of high-speed optical devices with polarization sensitivity. Here, we provide a comprehensive analysis of ultrafast chiroptical response of chiral gold nano-oligomers using time-resolved polarimetric measurements. We observe significant differences in terms of the absorption intensity, thus hot electron generation, and hot carrier decay time upon polarized photo-pumping, which are explained by a phenomenological model of the helicity-resolved optical transitions. Moreover, the chiroptical signal is switchable by reversing the direction of the pump pulse, demonstrating the versatile modulation of polarization selection in a single device. Our results offer fundamental insights into the helicity-resolved optical transitions in photoexcited chiral plasmonics and could facilitate the development of high-speed polarization-sensitive flat optics with potential applications in nanophotonics and quantum optics.) This article is protected by copyright. All rights reserved.