Optical Torques on Dielectric Spheres in a Spin‐Gradient Light Field
Abstract Light carries spin angular momentum, which can be imparted to the particle, generating an optical torque (OT). For decades, it has been widely understood that this spin‐induced OT only occurs on anisotropic (e.g., dumbbell and rod) particles or absorbing (e.g., gold) spheres. In contrast to previous interpretations, herein a nontrivial mechanism is presented for generating and measuring spin‐determined OTs on non‐absorbing spheres. This counterintuitive OT emerges from the gradient of the spin angular momentum, which imposes non‐uniformly distributed force/energy vectors on the particle. The opposite force vectors on both sides of the beam induce extraordinary spin‐gradient OTs whose sign depends on the particle's permittivity rather than its position. This negative spin‐gradient OT is more readily observable on dielectric particles due to the elimination of the predominant positive absorbing OT. Experimentally, the spin‐gradient OT is exquisitely measured using the polystyrene sphere delicately labeled with a tiny tail, showcasing its strong correlation with light polarization. The study enriches the fundamental understanding of OT, offering marvelous applications that circumvent heating effects in physical and biomedical sciences.
Authors
- Yuzhi Shi (ORCID: https://orcid.org/0000-0002-9041-0462)
- Zeyong Wei (ORCID: https://orcid.org/0000-0002-2347-1089)
- Zhanshan Wang (ORCID: https://orcid.org/0000-0002-6022-4933)
- Xiang Wu (ORCID: https://orcid.org/0000-0001-7936-2271)
- Qigang Wang (ORCID: https://orcid.org/0000-0002-4026-3337)
- Tao He (ORCID: https://orcid.org/0000-0001-9506-0011)
- Che Ting Chan (ORCID: https://orcid.org/0000-0002-9335-8110)
- Qinghua Song (ORCID: https://orcid.org/0000-0002-4622-0418)
- Bo Wang (ORCID: https://orcid.org/0000-0001-8088-1845)
- Haiyang Huang (ORCID: https://orcid.org/0000-0002-6000-3567)
- Xia Wang (ORCID: https://orcid.org/0000-0002-5256-0611)
- Pin Chieh Wu (ORCID: https://orcid.org/0000-0002-5781-9696)
- Minghe Jin (ORCID: https://orcid.org/0000-0001-6643-2824)
- Hong Luo (ORCID: https://orcid.org/0000-0003-2260-887X)
- Chengxing Lai
- Xinbin Cheng
- Weicheng Yi
Institutions
- Tongji University (CN)
- Shanghai Jiao Tong University (CN)
- Hong Kong University of Science and Technology (HK)
- Fudan University (CN)
- Tsinghua–Berkeley Shenzhen Institute (CN)
- National Cheng Kung University (TW)
- Tsinghua University (CN)
Publication Details
- Journal
- Laser & Photonics Review
- Published
- 2025-04-15
- DOI
- https://doi.org/10.1002/lpor.202500386
- Citations
- 2
- Primary Topic
- Orbital Angular Momentum in Optics
- Type
- article
- Field-Weighted Citation Impact
- 2.49
Funders
- National Natural Science Foundation of China
- Research Grants Council, University Grants Committee
- Shanghai Municipal Education Commission
- Science and Technology Commission of Shanghai Municipality
- National Key Research and Development Program of China
- Fundamental Research Funds for the Central Universities