Particle jumps between optical traps in a one-dimensional (1D) optical lattice

We address the problem of stochastic particle transitions between stable positions in a one-dimensional (1D) periodic potential profile. With respect to experimental realization, such stable positions are represented by the optical traps formed in an evanescent standing wave. The behaviour of sub-micrometre-sized particles in this 'optical potential energy landscape' is analysed theoretically and experimentally, and the emphasis is put on particle jumps between neighbouring optical traps. Our theoretical model assumes overdamped stochastic motion of a particle in a finite-depth potential well. Subsequently, the mean first passage time is utilized to express the new quantity called the mean optical trap escape time (MOTET), which describes the mean time of the particle escape to a neighbouring stable position (optical trap). Theoretical predictions of the MOTET are compared with the Monte-Carlo simulations and with the experimental results for similar parameters of the potential energy profile. This comparison reveals that the properties of the optical traps (trap stiffness and depth) can be obtained from the analysis of the MOTET for the experimentally observed particle jumps only if high-speed video microscopy is used and the surface-particle distance is known.