Scattering force in optical trapping

[pen]

hello,
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 ?
thanks.

 

[Andy Resnick]

For single-beam optical traps, the ray-optics limit (particle much larger than wavelength of trapping light) is treated here:

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1260270/pdf/biophysj00105-0286.pdf

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

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1523313/

and also Mazolli, Neto, Nussenzveig, Proc. R. Soc. Lond. (2003) 459, 3021-3041

 

[pen]

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]

Close enough, I'd say.

 

[sardar]

Hello,

Optical trapping is a fascinating phenomenon that has been extensively studied in the field of optics. The scattering force in optical trapping is a result of the interaction between light and matter. When a beam of light is directed towards a dielectric object, such as a small particle, the light is scattered in all directions due to the object's refractive index.

The scattering force is a combination of both specular reflection and refraction of the central rays. Specular reflection occurs when the incoming rays hit the surface of the object and are reflected at the same angle. This results in a force that pushes the object away from the center of the beam. Refraction of the central rays also contributes to the scattering force, as the change in the direction of the rays causes a change in the momentum of the object, resulting in a force.

It is important to note that the scattering force is not the only force at play in optical trapping. The gradient force, which arises from the variation in the intensity of the laser beam, also plays a significant role in trapping the object. In fact, the combination of the scattering and gradient forces is what allows for precise control and manipulation of small particles in optical trapping experiments.

I hope this helps to clarify your understanding of the scattering force in optical trapping. If you have any further questions, please don't hesitate to ask.

Best,