Perturbation between two traps in dual-trap optical tweezers

Lin Ling, Fei Zhou, Lu Huang, Honglian Guo, Zhaolin Li, and Zhi-Yuan Li

Dual-trap optical tweezers are widely used in biological sciences and many other areas. The two traps are generally considered to be independent of each other in most situations. But when they are close and even touch side by side, the influence may not be negligible. We calculate the optical force of dielectric spherical particles trapped in dual-trap optical tweezers by means of the discrete dipole approximation method and analyze the perturbation effect between the two traps. We find that the electric field does not change much when it is scattered by the trapped particles. As a result, the scattering light from one sphere has a little perturbation effect on the trapping force upon the other sphere. The perturbation mainly comes from the other trap and is thus affected by the distance between the two traps. In the experiment, the displacement of the sphere trapped in an immovable trap is observed when another trap is moving close. The experiment data of relative displacement match qualitatively with the calculation data.

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