Optical tweezers is an increasingly important technique for controlling and probing particles since computer-generated holography (CGH) make steering of multiple traps individually possible. In addition, the dark focus of orbital angular momentum (OAM) beams is increasingly widely used in trapping reflecting, absorbing or low-dielectric-constant objects. In this paper, we present a method to create arbitrary three-dimensional configurations of orbital angular momentum modes to achieve manipulation of micro-particles. Compared with conventional optical tweezers, this method can steer mixed arrays of traps individually and randomly by producing three-dimensional structure of optical vortices. These optical traps we used was formed by a CGH generated complex phase mask, which has three components: 1) a helical phase mask to change the transverse phase structure, 2) a blazed grating phase mask to vary the propagation direction of the incident beams, and 3) a modulated grating phase mask to divert the focal plane from the planar configurations. The latter one ensure that we can form threedimensional trapping patterns. The trap patterns can also be generated dynamically by holographic display system based on liquid crystal on silicon (LCoS). The experimental results show that the refresh frequency of reconfiguring achieves 24fps. Our method is effective and promise an exciting new opportunity to be used as a valuable non-contact manipulation tool in various applications.
Ting Xie, HuiHui Wang, Fei Yuan, Shengqian Chang, Peng Sun, Siman Zhang, Huaye Li, Siqi Liu, Chang Wang, and Zhenrong Zheng, "Arbitrary manipulation of micro-particles in three dimensions by steering of multiple orbital angular momentum modes," Proc. SPIE 10347, Optical Trapping and Optical Micromanipulation XIV, 103470Y (Presented at SPIE Nanoscience + Engineering: August 06, 2017; Published: 25 August 2017); https://doi.org/10.1117/12.2272165.
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