Open AccessInversion of gradient forces for high refractive index particles in optical trapping
Author(s) -
Leonardo André Ambrosio,
H.E. Hernández-Figueroa
Publication year - 2010
Publication title -
optics express
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.394
H-Index - 271
ISSN - 1094-4087
DOI - 10.1364/oe.18.005802
Subject(s) - trapping , refractive index , optics , optical tweezers , pressure gradient force , scattering , optical force , forward scatter , physics , light beam , dielectric , beam (structure) , materials science , optoelectronics , ecology , biology
The unexpected fact that a spherical dielectric particle with refractive index higher than the surrounding medium will not always be attracted towards high intensity regions of the trapping beam is fully demonstrated here using a simple ray optics approach. This unusual situation may happen due to the inversion of gradient forces, as shown here. Therefore, conventional schemes, such the one based on the use of two counter-propagating beams to cancel the scattering forces, will fail to trap the particle. However, effective trapping still can be obtained by adopting suitable incident laser beams.