Figure 3.

(a) Trajectories of a 642 nm silica bead trapped in the OT for 67 mW (green), 108 mW (red), and 129 mW (blue) of laser power without external perturbation. (b) Histograms of the trajectories shown in a, which are well fitted with Gaussian distribution. (c) Power spectra based on trajectories with external perturbation, from which K_OT can be obtained via the passive and active power-spectrum methods. For presentation, the three spectra (green, red, and blue) were vertically adjusted, although they overlap at lower frequencies. (d) Stiffness of the OT from the equipartition theorem method (triangles), passive power spectrum method (squares), and active power spectrum method (circles) for a 642 nm silica bead. Solid lines are the fit of the first three points, to show how much K_OT deviates at high power. To see this figure in color, go online.