Dynamical patterns of microscopic phase segregation under linear scanning of the focus of IR laser were investigated in a homogeneous oil/water mixture. When the scanning frequency is low, the generated oil droplet follows the motion of the laser focus. When the frequency is high, the generated oil droplet is located at a certain position. The mechanism of these characteristic trapping patterns is discussed in terms of the effective potential by the focused laser beam, which depends on the scan rate and the mode of scanning. (C) 2004 Elsevier B.V. All rights reserved.