Figure 1
From: Thermally induced micro-motion by inflection in optical potential
Principle of the experiment and examples of measured trajectories. Step 1: The particle (blue spot) is trapped in a single beam and follows Brownian motion in a quadratic potential close to its bottom. Step 2: The single beam is replaced with two co-propagating beams displaced in x-axis to form a non-linear single-well potential (dotted) with a cubic part (blue) along x-axis. Consequently the particle moves down the potential well (indicated by a blue arrow) passing through the cubic part and reaching the global minimum. Then the two beams are replaced with a single beam which confines the particle near the former global minimum and transports it to the initial position x 0. Steps 1 and 2 are repeated with the same particle to get a statistical ensemble. The dotted curve denotes the reconstructed potential profile (in k B T units) from the particle trajectories and a fit to the cubic potential profile gives μ 3 = (6.65 ± 0.05)k B T/μm3. A few measured trajectories are plotted as colour curves at the bottom part of the figure and the dashed one shows the deterministic trajectory without the influence of Brownian motion corresponding to T = 0.
