# Scattering force in optical trapping

• pen
In summary, the conversation discusses the theoretical background of optical trapping and how the scattering force originates. It is mentioned that the force can be due to reflection and refraction, and there are two different limits for calculating the net force in single-beam optical traps. The conversation also touches on the concept of scattering and gradient forces, and how they are affected by the incident angle of the ray.
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.

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 ?

Close enough, I'd say.

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,

## What is scattering force in optical trapping?

Scattering force in optical trapping is a phenomenon that occurs when a laser beam is focused on a small particle or molecule. The light scatters off the particle in all directions, creating a force that can trap the particle in place.

## How does scattering force work in optical trapping?

The scattering force is caused by the momentum transfer from the photons of the laser beam to the particle. As the photons scatter off the particle, they transfer momentum and create a force that traps the particle in the center of the laser beam.

## What are the applications of scattering force in optical trapping?

Scattering force in optical trapping has various applications in scientific research, including the manipulation and study of individual molecules, cells, and nanoparticles. It is also used in fields such as biophysics, nanotechnology, and materials science.

## How is scattering force measured in optical trapping?

The scattering force can be measured using a technique called optical tweezers. This involves tracking the motion of a particle trapped in the laser beam and using the particle's displacement to calculate the force acting on it.

## What are the factors that affect scattering force in optical trapping?

The scattering force in optical trapping is affected by various factors, such as the power and wavelength of the laser beam, the size and refractive index of the particle, and the properties of the surrounding medium. These factors can be adjusted to optimize the trapping force for different applications.

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