By using the hydrodynamic method,maximal transverse trapping forces on three kinds of micro-particles with radii ranging from 0.5 μm to 22 μm were measured by dragging these transparent dielectric beads suspended in water with the focused laser beam.The magnitude of trapping forces obtained from the experiment was of the order of pico-Newton.For PMMA particles of large size,the offset Δx of the particle from the optical trapping center was measured with different dragging velocities,and the trap...