Lateral mean exit time of a spherical particle trapped in an optical tweezer

We apply the Fokker-Planck equation to analyze the stochastic behavior of a 1-micron diameter polystyrene bead trapped in water using an optical tweezer. Due to thermal noise, given enough time, a trapped particle will escape confinement from the trap. However, at biological temperatures, for laser powers of greater than approximately 5 milliwatts at the focus, the mean first exit time in the lateral plane is extremely large, and unbounded for most practical purposes. We show that the mean exit time increases exponentially with laser power. Furthermore, for a trapped 9.6-micron diameter polystyrene bead, we show that experimental mean passage times within the linear trapping region are in close agreement with theoretical calculations.