Optical trapping with cylindrical vector beams

Recent development of cylindrical vector beams prompts its application in optical trapping, which shows more effective and improved trapping efficiency in contrast to the traditional Gaussian beam of spatially homogeneous polarization. Using the T-matrix method and vectorial diffraction theory, we calculated and compared the radiation forces exerted on dielectric particles respectively by the linearly polarized, radially polarized and azimuthally polarized beams. Theoretical calculations show that the radially polarized beam can improve the axial trapping efficiency of high-refractive-index larger particles by reducing the scattering force due to the vanishing axial component of Poynting vector near the focus, while the azimuthally polarized beam can not only steadily trap low-refractive-index small particles at the focus center but also can trap multiple high-refractive-index particles around the focus center in virtue of the hollow-ring configuration. The dependences of the trapping efficiencies on the beam parameters, particle size and the numerical aperture of objective lens are discussed. The performances of optical trapping, manipulating and sorting of biological cells, organelles and various micro-particles are demonstrated.