Lu Liangchen, Wen Jiquan, Lu Menglong, Ding Ping, Liu Jinyang, Zheng Hongxia, Chen Huajin
Opt Express. 2024 Aug 26;32(18):31344-31358. doi: 10.1364/OE.533355.
The optical pulling force is generally believed to originate from the recoil force due to the simultaneous excitation of multipoles in the particle, which overcomes the interception force contributing to the optical pushing force. However, we show that the interception force can induce optical pulling force on a small isotropic spherical particle with gain in a uniform electromagnetic plane wave, in which multipole excitation is negligible within the dipole regime. Based on the multipole expansion theory, a rigorous analytical expression is derived for optical force acting on a spherical particle of arbitrary size and composition illuminated by a single plane wave, regardless of its polarization. The analytical results show that the interception force, which is typically positive in a conventional dielectric particle under illumination of a single plane wave, undergoes a crossover from positive to negative by introducing appropriate gain into the dipolar dielectric nanoparticle, thereby giving rise to the optical pulling. It's deserved to be noted that the optical pulling force assisted by the interception force does not weaken in magnitude, in fact, it exhibits a stronger magnitude compared to the optical pushing force experienced by a corresponding conventional dielectric particle.
通常认为光拉力源于粒子中多极子同时激发产生的反冲力，该反冲力克服了导致光推力的拦截力。然而，我们表明，在均匀电磁平面波中，对于具有增益的小各向同性球形粒子，拦截力可诱导光拉力，在偶极子区域内多极子激发可忽略不计。基于多极子展开理论，推导了单个平面波照射下作用于任意尺寸和成分球形粒子上光力的严格解析表达式，而不考虑其偏振情况。分析结果表明，在单个平面波照射下，传统电介质粒子中的拦截力通常为正，通过在偶极电介质纳米粒子中引入适当的增益，拦截力会从正变为负，从而产生光拉力。值得注意的是，由拦截力辅助的光拉力在大小上并未减弱，事实上，与相应传统电介质粒子所经历的光推力相比，它表现出更强的大小。
