Probing interplay of light momentum and fluid mechanics in two-layer liquids

We present an experimental setup that utilizes a pump-probe laser configuration to investigate the interplay between light momentum and fluid mechanics in a two-layer liquid system. By inducing a nanometric bulge on the upper liquid layer, we observe the emergence of a transient bulge on the liquid-liquid interface propelled by viscous stress towards the liquid with a higher refractive index. Through the integration of noninvasive measurements and extensive numerical simulations, we successfully validate our experimental findings and elucidate the intricate interplay between light momentum theories [Minkowski, Math. Phys. Klasse 1908, 53 (1908); M. Abraham, Rend. Circ. Mat. Palermo 28, 1 (1909)] and fluid mechanics. Importantly, we demonstrate that the transient deformation height can serve as a valuable indicator of surface tension and viscosity, enabling precise nanoscale manipulation and holding great potential for advancements in sensors, actuators, and optical devices. The profound insights gained from this study offer significant promise for the advancement of microfluidics and optofluidics, driving progress in these fields.