The Nobel Prize in Physics: The Power of Light

Lisa Liu ’22

        Light is a part of our daily lives. Without light, we cannot see anything. Light seems to have no definite shape or form and is intangible, however, Arthur Ashkin, an optical physicist in Bell Telephone Laboratories in Murray Hill, New Jersey, presented to the world how light can capture and move things. On October 2nd, 2018, Ashkin received a half of the nine million Swedish krona awarded to Nobel Prize winners in Physics for his contribution in developing a light trap. The other half of the prize was shared among Gérard Mourou, Professor Haut-Collége at the École Polytechnique, and Donna Strickland, professor at University of Waterloo, for their technique of generating ultra-short, high-intensity light pulses.

        Ashkin was born on September 2nd, 1922 in New York and his major research was on Optical tweezers, commonly known as a light trap. Optical tweezers use laser beams to move or hold a tiny particle in place. Imagine a hand pushing a ball forward. If there is another hand of equal force pushing the ball in the opposite direction, the ball will stay in a stable position. In Optical tweezers, the hands are the light beams and the ball represents a tiny particle. As illustrated in the diagram, a particle can be pushed by the radiation pressure inside a light beam and move in corresponding speed and direction. Since the intensity of the pressure decreases from the center of the light beam to the outer surface, a particle inside the light is pressed to the middle. With two light beams pointing to the opposite directions facing each other, a particle in between is pushed by equal force on each side, therefore maintaining balance. However, two forces are not enough to keep a particle still in a three dimensional world. To ensure that a particle is not dropping because of gravity, Ashkin added another laser beam that points upward to balance out the downward force of gravity. In addition, Ashkin utilized an objective lens in each of the other two light beams to concentrate the light and intensify its force. His final Optical tweezer design was finally capable to hold a small particle at any place purely using lights.

        Ashkin’s design inspired many other scientists, and after many years of experimenting and optimizing the design for a stronger force, individual atoms could also be held in place by the light trap. While this research was still on going, Ashkin saw the great benefit of Optical tweezers in biological sciences. A major breakthrough came in 1987, when Ashkin used tweezers to capture living bacteria without harming them. Even though a simple holding of an atom in place is not significant, systems of more and higher-intensity light beams in different direction were invented, which allowed microscopic organic materials to be clearly observed. These light systems can even manipulate the sample without making any physical contact, thus preventing any destruction of the sample.

Nowadays, research in biological physics and related fields benefit from the Optical tweezers. For example, Optical tweezers are one of the vital instruments in investigating biological processes, such as proteins, molecular motors, single cells, organelles, DNA, and observing cellular movements at the microscopic level.

        “The inventions being honored this year have revolutionized laser physics. Extremely small objects and incredibly rapid processes are now being seen in a new light,” the Royal Swedish Academy of Sciences announced in press release. Ashkin’s idea and invention of Optical tweezers is not only special on its own but also in the sense that this new technology promotes future advancements in biological research. After all, even the best experiments need the right tools. Precise instruments like ultra-short optical pulses and the optical tweezers are important for, as Alfred Nobel once said, “the greatest benefit of humankind.”

        For more details on this year’s Nobel Prize in Physics, follow the link: This article draws on materials from American Institute of Physics, The Nobel Prize, The Optical Society, The Royal Swedish Academy of Sciences, and University of Michigan.Prolineserver 2010, Wikipedia/Wikimedia Commons