Broadband ultrafast self-heterodyned chiro-optical spectroscopy

Francesco Gucci†; Andrea Iudica†; Andres Valladares Y Tacchi†; Andrea Schirato; Giulia Crotti; Ryeong Myeong Kim; Soo Min Lee; Jeong Hyun Han; Andrea Villa; Dawar Ali; Aurora Rizzo; Margherita Maiuri; Ki Tae Nam; Giuseppe Della Valle; Giulio Cerullo

arXiv · 2511.10574

Broadband ultrafast self-heterodyned chiro-optical spectroscopy

Francesco Gucci†·Andrea Iudica†·Andres Valladares Y Tacchi†·Andrea Schirato·Giulia Crotti·Ryeong Myeong Kim·Soo Min Lee·Jeong Hyun Han·Andrea Villa·Dawar Ali·Aurora Rizzo·Margherita Maiuri·Ki Tae Nam·Giuseppe Della Valle·Giulio Cerullo

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Abstract

Ultrafast chiro-optical spectroscopy provides unique access to the structural dynamics of molecules, spin-valley relaxation in semiconductors, and the non-equilibrium optical response of chiral nanophotonic systems. Yet, because chiral signals are intrinsically weak and time-resolved spectroscopy probes small photoinduced changes, transient chiro-optical responses are often difficult to isolate from parasitic achiral contributions. Here, we introduce a broadband ultrafast chiro-optical spectroscopy technique that integrates a birefringent common-path interferometer with an optical polarization bridge to sensitively detect photoinduced changes in the polarization state of light. Phase-sensitive self-heterodyned detection enables simultaneous measurement of transient circular dichroism and optical rotatory dispersion across a broad spectral range with ultrafast temporal resolution. Balanced detection suppresses excess laser noise, enabling exceptional sensitivity (<50 ${\mu}$deg) close to shot-noise limit. We demonstrate this approach on an array of gold nano-helicoids, supported by a full-wave time-resolved model of the spatiotemporal dynamics of plasmonic non-equilibrium carriers and their associated optical nonlinearities. The model traces the system's transient chiro-optical response back to photoinduced modulations of the electric-magnetic dipole interaction in the nano-helicoid, elucidating the connection of near- and far-field dynamics in the non-equilibrium regime. We further investigate spin excitation, thermalization, and relaxation in a lead halide perovskite, establishing a novel approach to broadband time-resolved Faraday rotation. The simplicity, sensitivity, and wide applicability of this detection scheme provide a powerful platform for broadband ultrafast chiro-optical spectroscopy, opening new opportunities in biochemistry, solid-state physics, and nanophotonics.

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Francesco Gucci†, Andrea Iudica†, Andres Valladares Y Tacchi†, Andrea Schirato, Giulia Crotti, Ryeong Myeong Kim, Soo Min Lee, Jeong Hyun Han, Andrea Villa, Dawar Ali, Aurora Rizzo, Margherita Maiuri, Ki Tae Nam, Giuseppe Della Valle, Giulio Cerullo. 2025-11-13. Broadband ultrafast self-heterodyned chiro-optical spectroscopy. https://arxiv.org/abs/2511.10574

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