Nanoscale Interfacial Dynamics Unveil Photomolecular and Thermal Pathways of Evaporation

Light-matter interactions at fluid interfaces govern phenomena ranging from cloud microphysics to optofluidics, yet the mechanism by which light drives interfacial motion in weakly absorbing liquids remains unresolved. Here, we report polarization-dependent nonthermal light-induced dynamics at the air-water interface under green laser illumination, where bulk absorption is negligible. Using liquid-drop interferometry, we identify two distinct hydrodynamic time scales, τpm > τth, enabling clear separation of photomolecular and thermal contributions through their macroscopic interface response. The effect disappears when the pump polarization is switched from TM to TE, providing strong evidence of its nonthermal origin. We further demonstrate enhanced responses in whispering-gallery-mode microdroplets through repeated total internal reflections. These findings advance the understanding of light-driven interfacial dynamics, with potential implications for atmospheric radiative processes, optofluidics, and contactless optical manipulation of complex biofluid interfaces.