• Accepted Paper

Alignment-controlled optical orbital trapping of single airborne aerosols for dynamical particle sensing

Chun-Yen Wen, Yang-Yi Lee, Chung-Lin Chao, Ruei-Ying Jian, Tzu-Ling Chen, and Wayne Cheng-Wei Huang

Phys. Rev. Applied - Accepted 28 September, 2026

DOI: https://doi.org/10.1103/svcf-bmjj

Abstract

Optical forces in focused-beam traps are generally nonconservative, yet the controlled use of this nonconservative component for airborne single-particle dynamics remains limited. We demonstrate a dual-beam optical trap in which a single aerosol can be switched between localized confinement and sustained orbital motion by tuning the relative positions of two counter-propagating foci. The axial separation ∆D controls the onset of nonconservative circulation, while the lateral offset ∆R tunes the projected orbit size and causes a monotonic change in the rotation frequency. T-matrix optical force calculations and Langevin simulations support this interpretation by showing that finite axial misalignment activates a circulating force component, whereas near-zero axial separation gives a confinement-dominated force field. Experiments confirm the predicted switching behavior through mean-square displacement and frequency measurements. We further show that the projected orbit geometry provides a particle-dependent observable, with the orbit anisotropy Ay/Ax varying systematically with aerosol diameter. The results provide a compact, low-power platform for controlled orbital dynamics of single airborne particles and for future aerosol measurements based on nonequilibrium trajectory observables.

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