Affiliation:
1. Universidade Federal do Rio de Janeiro
2. Instituto Federal de Santa Catarina
3. Université de Strasbourg
4. Instituto Federal de Educação
Abstract
We demonstrate a bistable optical trap by tightly focusing a vortex laser beam. The optical potential has the form of a Mexican hat with an additional minimum at the center. The bistable trapping corresponds to a nonequilibrium steady state, where the microsphere continually hops, due to thermal activation, between an axial equilibrium state and an orbital state driven by the optical torque. We develop a theoretical model for the optical force field, based entirely on experimentally accessible parameters, combining a Debye-type nonparaxial description of the focused vortex beam with Mie scattering by the microsphere. The theoretical prediction that the microsphere and the annular laser focal spot should have comparable sizes is confirmed experimentally by taking different values for the topological charge of the vortex beam. Spherical aberration introduced by refraction at the interface between the glass slide and the sample is considered and allows us to finetune between axial, bistable, and orbital states as the sample is shifted with respect to the objective focal plane. We find overall agreement between theory and experiment for a rather broad range of topological charges. Our results open the way for applications in stochastic thermodynamics, as they establish a control parameter—the height of the objective focal plane with respect to the glass slide—that allows us to shape the optical force field in real time and in a controllable way.
Published by the American Physical Society
2024
Funder
Conselho Nacional de Desenvolvimento Científico e Tecnológico
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
Instituto Nacional de Ciência e Tecnologia de Fluidos Complexos
Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro
Fundação de Amparo à Pesquisa do Estado de São Paulo
Publisher
American Physical Society (APS)
Cited by
2 articles.
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