Speaker
Prof.
Yunlong Sheng
(Université Laval)
Description
For modeling optical trapping of an anisotropic nano-particle we first used the point matching
method to compute the T-matrix coefficients based on the boundary condition for the normal
componants of D-fields. In the anisotropic media, where the divergence of E-field is nonzero,
the Maxwell wave equations was sloved in the Fourier space. Thus, the plan waves with
angular spectrum amplitude distributions can be expanded into the orthogonal and complete
set of the Vector Spherical Wave Functions. The E-field eigenvectors can be obtained by the
characteristic equation. In the point-matching mthod however we do not need to solve the
entire internal field in the anisotropic particle, but an expression of the unknown internal field
at the boundaries. We computed the stress distribution on the interfaces of an anisotropic
nanocylinder and the related total lateral torque, spin torque and total force in the optical
tweezers in order to put in evidence for mecanism of the optical trap of the anisotropic
particle. The trapping beam was modeled as the vector Gaussian beam with high order
corrections. After solving the scattered field the radiation stress was computed through the
Maxwell stress tensor for anisotropic media by Robinson. Our calculation showed that
optical stress can be not normal to the interface of anisotropic media. Our calculation
predicted that when the optical axes of the anisotropic nanocylinder are not aligned with the
cylinder axis, the nanocylinder can be trapped inclined with respect to the beam axis at an
equilibrium position. Preliminary experimental observations came to support this prediction.
Abstract (100 words)
T-matrix
Author
Prof.
Yunlong Sheng
(Université Laval)
Co-author
Mr
Paul Bareil
(Université Laval)
