Fig. 3.
Side view of a 20-μm-diameter bead motion in the toroidal opto-thermocapillary flow. The bubble was generated at the origin in these graphs. (a) The motion of the bead in an r-z plane, as it circulates around the optothermally-generated bubble, using various laser pulse widths. A circle with 20-μm diameter is drawn on the graph to show the size of the bead. The portion of the overall bead trajectory that is used for manipulation is labeled as the “sub-flow region.” An artifact in the measured bead motion is apparent in the portion of the trajectory bounded by the black dashed lines, and is explained by Fig. S3 in the ESI. (b) The measured horizontal (Vr) and vertical (Vz) instantaneous velocity of the bead as a function of horizontal displacement along the r-direction. The laser pulse frequency was 20 Hz and the pulse width was 15 μs.