THEORETICAL DETERMINATION OF THE INFLUENCE OF THE POLARIZATION ON FORCES EXERTED BY OPTICAL TWEEZERS

摘要

Axial and lateral trapping forces of optical tweezers are theoretically investigated for latex spheres with radii between 0.4 mu m and 5 mu m, taking into account the plane of polarization of the laser beam. Assuming an infrared laser (lambda = 1.064 mu m) this regime corresponds to the intermediate regime (r approximate to lambda) between Rayleigh (r much less than lambda) and Mie scatters (r much greater than lambda) where currently discussed theories are no longer valid. A theoretical approach that uses the properties of Gaussian beams and takes the size of the microspheres and their sub-microscopic interaction with the surrounding medium into account is described. Axial and lateral trapping forces for three particle radii (0.5 mu m, 1.0 mu m, 5.0 mu) are presented depending on the polarization of the trapping beam. Significant differences are found for lateral forces parallel and perpendicular to the plane of polarization. Potential wells and spring constants are calculated for all particles and predictions for all directions are made for particles with an isotropic spring constant. Analytic expressions for the trapping position and the extension of the trapping range in the optical trap are derived. [References: 27]