为了分析聚焦光束对多层粒子的捕获效率, 结合矢量衍射积分、T矩阵方法以及Maxwell应力张量积分, 通过理论推导给出了双层球形粒子的T矩阵的详细表达式, 并对双层球形粒子在聚焦光场中的受力进行了数值计算, 详细分析了内层折射率和内层尺寸对光场捕获效率的影响。结果表明, 只有内层折射率在一定范围内, 聚焦光束对双层球形粒子才具有捕获作用, 随着内层折射率增加, 最大后向捕获效率先增加后减小至零, 对于空心粒子, 内层尺寸越大, 聚焦光束对粒子的捕获作用越弱, 且平面波的捕获作用比高斯光束更强。此双层球形粒子的受力计算可以拓展到多层的复杂粒子的情形。

In order to analyze the trapping efficiency of multi-layer particles in a focused beam, the T matrix of the double-layer spherical particle was deduced. The trapping force on double-layer spherical particles was numerically calculated by means of the vector diffraction integral combining the T matrix method and the Maxwell stress tensor integral. Effect of the refractive index and size of the inner layer on trapping efficiency was discussed in detail. The focused beam can trap the double-layer spherical particles only when the refractive index of the inner layer is appropriate. The maximum backward trapping efficiency will increase at first and decrease to zero finally when the refractive index increases. For hollow particles, the bigger the hollow is, the weaker the trap is. Besides, the trap formed by plane wave is stronger than Gaussian beam. The calculation method of the force on double-layer spherical particles can be expanded to the case of multilayer complex particles.