Second‐Harmonic Hyper‐Mie Optical Activity Enables Closed‐Loop Chiral Photochemistry

Abstract

ABSTRACT Photochemistry promises sustainable chemical processing but typically depends on ultraviolet light with limited selectivity and penetration. We report nonlinear chiral photochemistry, where femtosecond infrared pulses are frequency‐doubled to both drive and track a transformation of chiral CdTe/CdO nanohelices into CdO nanospheroids. Circularly polarized light induces a controlled oxidation sequence monitored in real time through second‐harmonic scattering intensity and chiroptical contrast. As the CdO shell fractures and exposes non‐centrosymmetric CdTe, second‐harmonic intensity rises twenty‐fold, polarization reverses, and characteristic CdTe photoluminescence emerges. These findings are enabled by the experimental observation of the second‐harmonic hyper‐Mie optical activity effect, which completes a suite of nonlinear chiroptical scattering phenomena predicted over 45 years ago. Our results offer a spatially confined, selective, and temporally‐resolved method for material transformation.