Extending the lateral trapping force of optical tweezers

Abstract

By increasing the axial trap stiffness, we demonstrate an increase of at least 50% in the maximum lateral trapping force that can be applied using optical tweezers. It has previously been shown that, using a novel method of compensating for spherical aberrations, the axial trap stiffness at any particular chosen depth within a sample can be increased. However, to our knowledge, the present paper is the first time this method has been used in combination with the drag force method for the purpose of more accurately determining the maximum lateral trapping force applicable by optical tweezers. Previous studies have substantially shown that before the actual maximum lateral trapping force can be reached, the particle escapes in the axial direction. Using a conventional setup, our studies support this conclusion. However, by employing the above mentioned method for improving the axial trap stiffness, we observed that the displacement of the bead in the lateral direction is increased by approximately 10%. This allows progress towards a more accurate determination of the maximum lateral force that can be applied using optical tweezers and could also permit a mapping of the trapping potential further from the trap's central region. Theoretical predictions made, show that the point where the maximum lateral force could be applied is at 0.9 a, where a is the radius of the trapped particle. However, the experimentally measured limit 0.55 a has until now been far lower than that theoretically predicted 0.9 a. In this proceeding, we demonstrate that the experimental limit can be extended to 0.61 a because of the decreased axial displacement of the bead.