Light is used by optical tweezers to control microscopic objects the size of a single atom. A focused laser beam generates radiation pressure which is capable of trapping small particles.
How Do Optical Tweezers Work?
A high quality microscope objective is used to focus a laser beam to a "dot" in the specimen. This dot then creates an optical trap which is capable of holding a tiny particle at its center. The forces experiences by this tiny particle composed of gradient forces and light scattering. Gradient forces are the result of the interactions between the particle and light.
Typical optical microscopes are frequently modified and used for the construction of optical tweezers. Optical tweezers have progressed from straightforward tools to control objects on the micro-scale to state-of-the-art instruments controlled by computers able to precisely and accurately measure displacements and forces.
Principles Behind Operations of Optical Tweezers
The fundamental principle behind optical tweezers is the transfer of momentum related to the bending of light. Momentum is carried by light and is equivalent to the direction of propagation and its energy. Any changes in the momentum of light are the result of directional changes of light caused by reflection or refraction.
When light is bent by an object, a change in momentum is resulted. The preservation of momentum involves the object to experience an equal and opposite change in momentum. This leads to a force is being experienced by the object.
Applications of Optical Tweezers
Dielectric spheres, bacteria, living cells and tiny metal particles have been trapped using optical tweezers. Optical trapping are also being used in the fields of biology for the study of molecular motors and the physical properties of DNA.