拉盖尔-高斯光束是典型的涡旋光束,光束的轨道角动量会传递给微粒使其产生轨道运动。本文利用T矩阵方法和麦克斯韦应力张量积分计算了强聚焦线偏振拉盖尔-高斯光束对球形粒子的捕获力,并着重分析了粒子半径和光束阶数对微粒在涡旋聚焦场中运动状态的影响。当光束阶数一定时,随着微粒半径的增大,轨道运动的轨迹会逐渐缩小。当粒子半径大于临界值时,就会被捕获到光轴上,且无法进行轨道运动。但是,离轴捕获的粒子受到的轴向捕获力比轴上捕获的要小一个量级,需要施加足够的入射光功率以维持稳定的轨道运动。

Laguerre-Gaussian beams are typical vortex beams,the orbital angular momentum of the beam can be transmitted to the microsphere and make it do an orbital motion.The trapping forces exerted by the highly focused linearly polarized Laguerre-Gaussian beam (LGB) on a spherical particle are calculated by means of the T-matrix method and Maxwell stress tensor integral.The impact of microsphere radius and beam order on the particle′s trapping states in the vortex focusing field are investigated.When the topological charge keeps constant,with the microsphere′s radius increases,the trajectory of the orbital motion will gradually shrink.As its radius is larger than the critical value,the microsphere will be trapped on the optical axis without orbital motion.However,axial trapping forces of particles trapped off-axis are smaller an order of magnitude than those of particles trapped on axis,so that more input optical power is needed to maintain the stable orbital motion.