Nanomechanics of Light in Fluids and Their Implications beyond the Abraham–Minkowski Controversy

We demonstrate tunable optical forces at an air–water interface through the precise control of water layer thickness and spot size of the pump laser beam. By varying the water layer thickness from a few millimeters to several centimeters, we identify a critical depth-to-spot size ratio at which the light pressure sign changes and produces the dimples on the air–water interface. Using numerical simulations under realistic experimental conditions, we show that the velocity profile induced by light pressure of tens of micrometers per second induces shape transformations of the air–water interface. We emphasize that this study, although providing new insights into the nanomechanical effects of light pressure on fluids, does not have any influence on the famous Abraham–Minkowski problem, contrary to what is often asserted in the literature. The reason is that the time variations of physical quantities are insufficient to make themselves observable experimentally.