Stable optical lateral forces from inhomogeneities of the spin angular momentum

Yuzhi Shi; Tongtong Zhu; Jingquan Liu; Din Ping Tsai; Hui Zhang; Shubo Wang; Che Ting Chan; Pin Chieh Wu; Anatoly V Zayats; Franco Nori; Ai Qun Liu

doi:10.1126/sciadv.abn2291

Stable optical lateral forces from inhomogeneities of the spin angular momentum

Sci Adv. 2022 Dec 2;8(48):eabn2291. doi: 10.1126/sciadv.abn2291. Epub 2022 Nov 30.

Authors

Yuzhi Shi^{1

2

3

4}, Tongtong Zhu⁵, Jingquan Liu⁶, Din Ping Tsai⁷, Hui Zhang⁸, Shubo Wang⁹, Che Ting Chan¹⁰, Pin Chieh Wu¹¹, Anatoly V Zayats¹², Franco Nori^{13

14}, Ai Qun Liu⁸

Affiliations

¹ Institute of Precision Optical Engineering, School of Physics Science and Engineering, Tongji University, Shanghai 200092, China.
² MOE Key Laboratory of Advanced Micro-Structured Materials, Shanghai 200092, China.
³ Shanghai Institute of Intelligent Science and Technology, Tongji University, Shanghai 200092, China.
⁴ Shanghai Frontiers Science Center of Digital Optics, Shanghai 200092, China.
⁵ School of Optoelectronic Engineering and Instrumentation Science, Dalian University of Technology, Dalian 116024, China.
⁶ National Key Laboratory of Science and Technology on Micro/Nano Fabrication, Shanghai Jiao Tong University, Shanghai 200240, China.
⁷ Department of Electrical Engineering, City University of Hong Kong, Hong Kong, China.
⁸ School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798, Singapore.
⁹ Department of Physics, City University of Hong Kong, Hong Kong, China.
¹⁰ Department of Physics, The Hong Kong University of Science and Technology, Hong Kong, China.
¹¹ Department of Photonics, National Cheng Kung University, Tainan 70101, Taiwan.
¹² Department of Physics and London Centre for Nanotechnology, King's College London, London, UK.
¹³ Theoretical Quantum Physics Laboratory, RIKEN Cluster for Pioneering Research, Wakoshi, Saitama 351-0198, Japan.
¹⁴ Physics Department, University of Michigan, Ann Arbor, MI 48109-1040, USA.

Abstract

Transverse spin momentum related to the spin angular momentum (SAM) of light has been theoretically studied recently and predicted to generate an intriguing optical lateral force (OLF). Despite extensive studies, there is no direct experimental evidence of a stable OLF resulting from the dominant SAM rather than the ubiquitous spin-orbit interaction in a single light beam. Here, we theoretically unveil the nontrivial physics of SAM-correlated OLF, showing that the SAM is a dominant factor for the OLF on a nonabsorbing particle, while an additional force from the canonical (orbital) momentum is exhibited on an absorbing particle due to the spin-orbit interaction. Experimental results demonstrate the bidirectional movement of 5-μm-diameter particles on both sides of the beam with opposite spin momenta. The amplitude and sign of this force strongly depend on the polarization. Our optofluidic platform advances the exploitation of exotic forces in systems with a dominant SAM, facilitating the exploration of fascinating light-matter interactions.