Tweezer

Optical tweezer is a device used to trap the micro level particles by using Laser, since laser have very high intensity with a high coherence length to trap the particle. In this method, we impose optical beam on a particle and beam is scattered by the particle and the particle is trapped due to the forces applied in this.

There are two types of particle can be trap by using this technique

 particle smaller than the 1 micro meter Mie particle

 particle bigger than the 1 micro meter Raleigh particle

For trapping micron level particle we need scattering force, gradient force and gravitational force. For trapping sub-micron level particle, we need scattering force, gradient force, thermal heating and gravitational force, which works on the particle and cancel out each other, so the total force on he particle is zero.Since in case of nano particle the differection limit of the source is very important parameter which depends on the wavelength.

This is the schemetic diagram of system.

 A new technology called haptic optical tweezers allows microscope users to manipulate samples by sight and touch, which could improve dexterity of micromanipulation and microassembly. 

The tweezers “will become an invaluable tool for force feedback micromanipulation of biological samples and nano- and microassembly parts,” said Dr. Cécile Pacoret of Université Pierre et Marie Curie (UPMC), a co-author of the study. 



There are two type of particles .
micron particles 
sub micron particles


Micron Particles: In this type of particles Scattering and gradient forces. Scattering force is applied in the direction of propagation of optical beam. Where as gradient force is applied towards the center of the focus. When gradient force is greater than scattering force we can trap the particle.