Journal
JOURNAL OF THE OPTICAL SOCIETY OF AMERICA A-OPTICS IMAGE SCIENCE AND VISION
Volume 27, Issue 9, Pages 2061-2071Publisher
Optica Publishing Group
DOI: 10.1364/JOSAA.27.002061
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- Research Councils of the United Kingdom (RCUK)
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A theoretical examination of off-axial trapping in non-paraxial Laguerre-Gaussian beams is presented for both the Rayleigh and Mie regimes. It is well known that the force acting on a particle may be divided into a term proportional to the intensity gradient and another representing the scattering force. The latter term may be further sub-divided into a dissipative radiation force and a term dependent on the electric field gradient. For Rayleigh particles in Laguerre-Gaussian beams, it is shown that the field gradient term contributes exactly half of the scattering force. This may be compared with a plane wave, in which it makes zero contribution. The off-axis trapping positions for spheres with radii varying from 0.1 to 0.5 mu m and a range of refractive indices are calculated numerically in the Mie regime, using a conjugate gradient approach. Azimuthal forces and orbital torques are presented for particles in their trapping positions, for beams with different orbital angular momentum and polarization states. The components of a spin torque, acting through the center of the particle, are also computed for absorbing particles in the Mie regime. (C) 2010 Optical Society of America
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