Spatial stability of particles trapped by time-modulated optical potentials

Time-division multiplexing in the proposed holographic optical tweezers has been used to quasi-simultaneously generate two different intensity patterns, a carrier beam spot and a beam array, by alternately sending the corresponding hologram patterns to a spatial light modulator. Since the switching of the input holograms degrades the spatial stability of a Brownian particle trapped within the generated intensity spot area, it is necessary to numerically investigate the conditions in the time-division multiplexing for a particle to be stably trapped in a focused Gaussian beam. A potential field generated by the beam spot is analytically calculated by the generalized Lorenz-Mie theory model, and the spatiotemporal stability of the particle trapped within the potential field is numerically investigated by the Smoluchowski equation. The simulation based on the explicit method reveals the spatiotemporal stability of the trapped particle related to the particle size, the switching rate, and the focused laser beam power. Finally, the validity of the numerical analysis in this work is confirmed by experiments.