Laser Manipulation of Bubbles and Evaluation of Its Optical Force

Abstract

We develop a laser trapping method in order to control the position of bubbles out of contact. In this method, a thin laser beam that is scanned so as to trace a corn is focused into the liquid by using an immersion objective lens or a dry objective lens. This method is adequate to trap a rising bubble because the potential barrier made by the light momentum change due to the reflection and refraction on the bubble surface exists only at the upper side of the bubble. Moreover, the usage of the dry objective lens with large working distance has an advantage that the influence of the lens on the bubble is negligible because the objective lens can be set up outside the liquid. Bubbles of the order of 10 μm in diameter have been trapped and manipulated successfully by using the dry objective lens as well as the immersion objective lens. We also evaluate the optical force acting on a bubble both experimentally and theoretically. Trajectories of rising bubbles are predicted by taking account of the optical force. It is shown that the optical force in the lateral direction is weaker than that in the axial direction.