Laser-induced hybrid trap for micro-bubbles

Micro-bubbles have been stably trapped in liquid ethanol by a focused argon laser beam. Two equilibrium points where bubbles can be trapped are observ ed to be at the center and the rim of the laser beam. The light force is al so able to push a bubble into the liquid to a position well below the liqui d surface. Both the light-pressure force and the fluid force induced by the convection of the liquid medium are calculated. The results clearly show t hat these two kinds of forces account for the formation of trapping potenti al.