聚焦光场俘获微球的FDTD分析

Study on trapping force of focused optical field on the microsphere with the FDTD method

基于动量守恒原理,采用2维时域有限差分方法(2D FDTD)建立了激光场对微米量级微球的作用力模型,讨论了入射高斯光场的波长、束腰半径、微球的折射率和半径等对聚焦光场俘获力的影响.结果表明:位于聚焦光场中特定位置的微球可被俘获,当离轴距离增加,俘获力减小.微球所受到的俘获力与微球的折射率有关,当小于环境折射率时(如汽泡),不能形成俘获,而被推离光场.模拟结果与其他文献中报道的实验结果一致.

The model of trapping force on microsphere based on the conservation of momentum are presented. Using 2-D FDTD algorithm, we calculated the effects of the wavelength, waist of the Gaussian beam, the radius and refractive index of the mierosphere on the trapping force. The results show that the microsphere located in a certain zone of focused laser optical electromagnetic fields will be trapped, and the trapping force deceases with the increase of the distance of the observed point away from the axis. When the refractive index of the surrounding medium is greater than that of the microsphere （such as an air bubble）, it will be pushed out of the laser beam. The simulation results are in good aggrement with the experimental observation.