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Scattering force in optical trapping

by pen
Tags: force, optical, scattering, trapping
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Mar26-14, 04:34 AM
P: 6
reading about the theoretical background of optical trapping. I was wondering how the scattering force originates. Often it is written, that the scattering force is due to reflection, but also the central rays refracted by a dielectric object should contribute ? So the scattering force is due to specular reflection of the incoming rays and refraction of the central rays ?
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Andy Resnick
Mar26-14, 08:22 AM
Sci Advisor
P: 5,523
For single-beam optical traps, the ray-optics limit (particle much larger than wavelength of trapping light) is treated here:

The other limit, corresponding to Rayleigh scattering, requires use of physical optics and is treated here:

and also Mazolli, Neto, Nussenzveig, Proc. R. Soc. Lond. (2003) 459, 3021-3041
Mar26-14, 12:02 PM
P: 6
thanks a lot! now I think:

in the ray optics regime:

The net force exerted on a microsphere by one ray is calculated considering the contribution of forces due to reflection and due to refraction, (depending on the incident angle of the ray).

The net force can be decomposed into scattering (defined as parallel to the incident ray) and the gradient force (defined as perpendicular to the incident ray).

A ray of large incident angles (with respect to the optical axis) has a higher ratio of gradient force/scattering force.

hope it`s not that wrong ?

Andy Resnick
Mar28-14, 11:49 AM
Sci Advisor
P: 5,523
Scattering force in optical trapping

Close enough, I'd say.

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