Quantitating Trapping Stability of Optical Tweezers in a Dynamic Flow

Optical tweezers (OTs) can immobilize and manipulate objects with sizes that span between nano- and micro-meter scales. The manipulating ability of OTs is usually characterized by stability factor (S) which can only indicate an empirical “hit-or-miss” process. Moreover, traditional analytical models of optical trapping lack accuracy in representing the trapping characteristics because they overlook key parameters imposed by dynamic systems so that S cannot quantitatively describe the state of trapping. In this paper, a comprehensive quantitative analysis of the optical trapping stability in a perturbed dynamic potential well is presented, especially for weakly trapping scenarios, from the perspective of statistics. Our novel, analytical formulation takes experimentally measurable parameters including particle size, optical power and spot width as inputs and precisely outputs a statistically relevant mean trapping time as output. Especially, this formulation takes into account general and realistic cases including fluidic flow velocity and other perturbations. With a back-focal-plane-interferometer-monitored trapping experiment in a flow, the statistic characteristics of trapping time demonstrates good agreement with theoretical predictions. In total, the model quantitative reveal the effects of external disturbance on trapping time, which will find applications where optical trapping stability is challenged by external perturbations in weakly trapping conditions.