Optical Tweezers

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"Don't exaggerate Ashkin" people said to Arthur Ashkin, winner of Physics Nobel prize 2018 when he described the idea of catching living things with light.

Unconventional thinking and innovative ideas always lead to the origin of new research areas and the development of advanced techniques in Physics. Optical tweezers invented by Arthur Ashkin is one such extraordinary invention in recent times. Ashkin working at Bell Laboratories in New Jersey became interested in applying a laser's intense beam to move small objects directly with the light field rather than through some effect of laser-generated heat.

As a consequence of the extensive work on manipulating microparticles with laser light Arthur Ashkin designed optical tweezers. Optical tweezers, more accurately called a single-beam optical trapping technique, have become a widely used versatile method for noncontact manipulation of microparticles, cells, and even molecules and as a tool for the measurement of piconewton force.

An optical trap is created by bringing a laser light to sharp focus into the cone through a microscope objective of high numerical aperture. At this high-intensity focal spot of laser, microparticles experience optical forces and get trapped. How do optical forces come into the picture? We all know light carries momentum. When light undergoes reflection or refraction there is a change in the direction of light. Any directional changes cause a change in the momentum of light which is imparted to the particle to satisfy the conservation of momentum. This transfer of momentum gives rise to optical forces on the particle.

Optical tweezers have been used to trap dielectric spheres, small metal particles, viruses, bacteria, living cells, and even strands of DNA. The field of optical tweezers is growing tremendously and being customized to expand the information of scientific areas such as atomic physics, optics, and biological science.


By,

Shivaraj Karjagi

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