Interaction of two bubbles near a free surface

Two bubbles are simultaneously generated in a line perpendicular to a free surface by focusing two Q-switched ruby laser beams into tap water. The dynamic behavior of the induced bubbles is investigated by means of high-speed photography. It is found that the period of the motion of the upper bubble becomes longer than that of a single bubble near a free surface as the mutual distance between two bubbles becomes shorter. If the two bubbles are much different in size, we observed counterjet formation, bubble splitting and interpenetration.