  We report on a new class of electromagnetically-driven fluid interface
instability. Using the optical radiation pressure of a cw laser to bend a very
soft near-critical liquid-liquid interface, we show that it becomes unstable
for sufficiently large beam power P, leading to the formation of a stationary
beam-centered liquid micro-jet. We explore the behavior of the instability
onset by tuning the interface softness with temperature and varying the size of
the exciting beam. The instability mechanism is experimentally demonstrated. It
simply relies on total reflection of light at the deformed interface whose
condition provides the universal scaling relation for the onset Ps of the
instability.
