Optical Activity Modulation in Chiral Metasurfaces via Structured Light

We demonstrate a real-time, all-optical method for modulating optical activity in chiral metasurfaces using structured light without altering the metasurface geometry. By employing tightly focused Laguerre-Gaussian beams carrying spin and orbital angular momentum, we achieve dynamic control of the dichroism through selective excitation of optically dark multipolar modes. Unlike conventional methods reliant on thermal, mechanical or chemical stimuli, our approach offers noninvasive, and reversible modulation, overcoming key limitations in response time and energy efficiency. The structured light's field gradients enable access to optical modes otherwise inactive under plane wave illumination. This technique opens new pathways for adaptive nanophotonic systems, including quantum sensors, polarization controllers, and quantum encryption platforms, where high-speed and contactless tuning of chiroptical properties is essential.