Understanding Physics of 2018 Nobel Winners

by Promod Puri

We are quite familiar with tweezers, the small nippers for plucking out unwanted hairs or extracting splinters.

But when these little tools are made of light beams to hold very tiny objects in scientific and medical fields, the optical tweezers play quite a significant role as technical aids in the studies of motions and behavior of molecular or cellular particles.

That precisely the reason the 2018 Nobel Prize in physics has been awarded to Arthur Ashkin for his works on optical tweezers.

Other co-winners of the Nobel Prize in physics are Gerard Mourou and Canadian scientist Donna Strickland for creating the technology which generates high-intensity, ultra-short laser pulses, which are used for eye surgeries and for studies of the extremely fast phenomenon in the atomic domain.

Light is more than making things visible. It is also a force. When applied to a physical object it is called radiation pressure. In this application, a coherent beam of light known as the laser is focussed on the object. An optical tweezer is created by two laser beams coming from the opposite direction and falling on the matter.

“In 1969, Arthur Ashkin used lasers to trap and accelerate micron-sized objects such as tiny spheres and water droplets. This led to the invention of optical tweezers that use two or more focused laser beams aimed in opposite directions to attract a target particle or cell toward the center of the beams and hold it in place. Each time the particle moves away from the center, it encounters a force pushing it back toward the center”, explains Todd Adams, Professor of Physics, Florida State University, in his article in The Conversation.

While the Nobel recognized the works of optical tweezers by Ashkin, the development of other optical tools from light beams also has an essential contribution for generating high-intensity and ultra-short laser pulses. These intensified bursts of light are now the tools for eye surgeries. The pioneer works of Mourou and Strickland in developing these tools have earned them the Nobel Prize.

The two physicists invented the way to create intense light but for the extremely short duration. These are bursts or pulses of light of ultrashort-term in an attosecond, which is trillionth of a second.

“As an analogy, consider a thick rubber band. When the band is stretched, the rubber becomes thinner. When it is released, it returns to its original thickness. Now imagine that there is a way to make the stretched rubber band thicker. When the band is released, it will end up thicker than the original band. This is essentially what happens with the laser pulse”, writes Professor Adams.

The thicker or high-intensity laser bursts are used in eye surgeries and for studying ultra-fast activities at the atomic levels.

“The 2018 Nobel Prize in physics shines a light on the pioneering work of these three scientists. Over the past three decades, their inventions have created avenues of science and medical treatments that were previously unattainable”, Professor Adams concludes in his article.

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