Figure 4. Separation of translation and precession of a SNW in an optical trap.

(a) Dual image tracking within two image planes. The IP1 is fixed at the center of the SNW motion. The IP2 moves along the vertical direction with a 50-nm step. (b) Three-dimensional images of the SNW were constructed by stacking the lateral displacements (x₂, y₂). The displacements result from both the translation and precession of the SNW. From the dual image tracking, the translational motion and the rotational motion of the SNW can be measured, respectively. The translational motions of the SNW’s center are shown in (c), and the relative lateral displacements (x₂-x₁, y₂-y₁), which depend only on the precession of the SNW, are shown in (d).