Figure 7.6 — Simulation of the motion of an optically trapped particle Figure 7.6 — Simulation of the motion of an optically trapped particle. (a) Trajectory of a Brownian particle in an optical trap (κx = κy = 1.0 fN/nm and κz = 0.2 fN/nm). The particle explores an ellipsoidal volume around the centre of the trap, as evidenced by the shaded area, which represents an equiprobability surface. The probability densities of finding the particle in the (b) xz and (c) xy planes follow a two-dimensional Gaussian distribution around the trap centre. The simulations correspond to a silica microparticle in water with radius a = 1 μm, mass m = 11 pg, viscosity η = 0.001 Ns/m2, γ = 6πηa, temperature T = 300 K and τm = 0.6 μs.Adapted with permission from Volpe and Volpe, Am. J. Phys. 81, 224–30. Copyright 2013, American Association of Physics Teachers.