Calculation Optical Trapping Forces Of Optical Tweezers With Cylindrically Symmetric Vector Beams

Optical tweezers technology acts as a powerful tool in the field of bio-medical and physical science for trapping small particles and bio-molecules. This technology has been widely used and attracted by many researchers all over the world due to its good features like non-contact and no-injury trapping property. Cylindrically symmetric vector beam has the unique polarization state and light distribution characteristics, which receives much concern in the field of optical trapping based on single beam light. Calculation method of optical trapping and evaluation of different parameters of such beams will help us to better understand and apply optical tweezers technology to improve the performance of existing optical tweezers. In this paper, the synthesis methods, optical field distribution and trapping efficiency of radial and azimuthal polarized beams are discussed based on previous research results. And the influence of relative parameters to optical trapping efficiency are analyzed. The main works and conclusions of this paper are listed as follows:(1)The numerical simulation of geometrical optics model is used to calculate the trapping efficiency with beams in different polarized modes. And the numerical result of electromagnetic scattering model which is based on MATLAB Optical Tweezers Toolbox is also calculated for comparison. The feasibility of the calculation of optical trapping of cylindrically symmetric vector beams is verified in Optical Tweezers Toolbox. Then the advantages and disadvantages of the two modes is discussed by optical trapping calculation. It is shown that the improved Optical Tweezers Toolbox is able to calculate the optical trapping of cylindrically symmetric vector beams. Compared with the numerical results of geometrical optics model, the results of electromagnetic scattering model which is based on MATLAB Optical Tweezers Toolbox is more identical with actual analysis.(2)Based on the improved Optical Tweezers Toolbox, the calculation of optical trapping of cylindrically symmetric vector beams which was synthesized by the superposition of two linearly polarized TEM01 mode beams is realized. And the two circularly polarized LG01 beams do the same task. By comparing their results, it can be found that the calculation result of the optical trapping of cylindrically symmetric vector beams which is synthesized by these two methods are consistent in the calculation of optical trapping.(3)The special trapping properties of cylindrically symmetric vector beams are discussed. The results show that radial polarized beam has an advantage of trapping particles which with relatively large refractive index. It is more stable than other beams in the axial trapping. However, azimuthal polarized beam is suitable for particles with relatively small refractive index, which has multiple equilibrium positions in the transverse trapping, and azimuthal polarized beam can capture more small size particles at the same time. For the optical trapping of small sized particles whose refractive index is lower than the surrounding medium environment, azimuthal polarized beam could trap these particles in the transverse trapping due to its special optical field features.