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Stable optical lateral forces from inhomogeneities of the spin angular momentum

Research output: Contribution to journalArticlepeer-review

Original languageEnglish
Article numbereabn2291
Pages (from-to)eabn2291
JournalScience Advances
Issue number48
Accepted/In press17 Oct 2022
Published2 Dec 2022

Bibliographical note

Funding Information: Y.S. was supported by the Fundamental Research Funds for the Central Universities. Y.S. and A.Q.L. acknowledge the Singapore Ministry of Education (MOE) Tier 3 grant (MOE2017-T3-1-001), Singapore National Research Foundation grant (MOH-000926), A*STAR research grant (SERC A18A5b0056), and Singapore’s National Water Agency grant (PUB-1804-0082). F.N. is supported, in part, by Nippon Telegraph and Telephone Corporation (NTT) Research, the Japan Society for the Promotion of Science (JSPS) [via the Grants-in-Aid for Scientific Research (KAKENHI), grant no. JP20H00134], the Army Research Office (ARO) (grant no. W911NF-18-1-0358), the Asian Office of Aerospace Research and Development (AOARD) (via grant no. FA2386-20-1-4069), and the Foundational Questions Institute Fund (FQXi) via grant no. FQXi-IAF19-06. D.P.T. acknowledges the support from the UGC/RGC of the HKSAR, China (project no. AoE/P-502/20 and GRF project 15303521); the Department of Science and Technology of Guangdong Province (no. 2020B1515120073); the Shenzhen Science and Technology Innovation Commission (grant no. SGDX2019081623281169); and the City University of Hong Kong (grant no. 9380131). T.Z. acknowledges the Natural Science Foundation of China (NSFC), grant no. 12104083. A.V.Z. acknowledges the support from the ERC iCOMM project (789340). P.C.W. acknowledges the support from the Ministry of Science and Technology (MOST), Taiwan (grant nos. 107-2923-M-006-004-MY3, 108-2112-M-006-021-MY3, and 110-2124-M-006-004), and, in part, from the Higher Education Sprout Project of the Ministry of Education (MOE) to the Headquarters of University Advancement at National Cheng Kung University (NCKU). P.C.W. also acknowledges the support from the Ministry of Education (Yushan Young Scholar Program), Taiwan. Funding Information: Acknowledgments Funding: Y.S. was supported by the Fundamental Research Funds for the Central Universities. Publisher Copyright: Copyright © 2022 The Authors.


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    Uploaded date:07 Dec 2022

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King's Authors


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.

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