Inverse Optical Torques on Dielectric Nanoparticles in Elliptically Polarized Light Waves
Yuzhi Shi, Tongtong Zhu, A. Q. Liu, Lei‐Ming Zhou, M. Nieto‐Vesperinas, Amir Hassanfiroozi, Jingquan Liu, Din Ping Tsai, Zhenyu Li, Weiqiang Ding, Fan Wang, Hang Li, Qinghua Song, Xiaohao Xu, Baojun Li, Xinbin Cheng, Pin Chieh Wu, C. T. Chan, Cheng‐Wei Qiu
Abstract
Elliptically polarized light waves carry the spin angular momentum (SAM), so they can exert optical torques on nanoparticles. Usually, the rotation follows the same direction as the SAM due to momentum conservation. It is counterintuitive to observe the reversal of optical torque acting on an ordinary dielectric nanoparticle illuminated by an elliptically or circularly polarized light wave. Here, we demonstrate that negative optical torques, which are opposite to the direction of SAM, can ubiquitously emerge when elliptically polarized light waves are impinged on dielectric nanoparticles obliquely. Intriguingly, the rotation can be switched between clockwise and counterclockwise directions by controlling the incident angle of light. Our study suggests a new playground to harness polarization-dependent optical force and torque for advancing optical manipulations.