Theory of trapping forces in optical tweezers

Starting from a Debye-type integral representation valid for a laser beam focused through a high numerical aperture objective, we derive an explicit partial-wave (Mie) representation for the force exerted on a dielectric sphere of arbitrary radius, position and refractive index. In the semi-classica...

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Bibliographic Details
Published in:Proceedings of the Royal Society. A, Mathematical, physical, and engineering sciences Mathematical, physical, and engineering sciences, 2003-12, Vol.459 (2040), p.3021-3041
Main Authors: Mazolli, A., Maia Neto, P. A., Nussenzveig, H. M.
Format: Article
Language:English
Subjects:
Approximation
Coefficients
Electric fields
Laser beams
Magnetic fields
Mie Scattering
Multipoles
Optical Traps
Semiclassical Limit
Sine function
Stiffness
Tweezers
Wavelengths
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Summary:Starting from a Debye-type integral representation valid for a laser beam focused through a high numerical aperture objective, we derive an explicit partial-wave (Mie) representation for the force exerted on a dielectric sphere of arbitrary radius, position and refractive index. In the semi-classical limit, the ray-optics result is shown to follow from the Mie expansion, holding in the sense of a size average. The equilibrium position and trap stiffness oscillate as functions of the circumference-to-wavelength ratio, a signature of interference, not predicted by previous theories. We also present comparisons with experimental results.
ISSN:1364-5021
1471-2946
DOI:10.1098/rspa.2003.1164