Arthur Ashkin, Ph.D. ’52, who won the Nobel Prize in physics in 2018 for pioneering “optical tweezers” that use laser light to capture and manipulate microscopic particles, died Sept. 21 at his home in Rumson, N.J. He was 98.
Over the course of several decades, Ashkin evolved his method of trapping micron-sized particles, such as atoms and molecules, to also trap biological organisms, such as viruses and bacteria, and even stretch DNA. The technique has enabled researchers to explore these and other delicate materials without directly touching them. It is now widely used in a range of biological and medical applications, as well as in quantum optics and nanoengineering.
“With Arthur Ashkin’s passing we have lost a legendary scientist,” said Steven Adie, associate professor in the Meinig School of Biomedical Engineering, whose own research has been influenced by Ashkin. “Ashkin’s pioneering work continues to inspire today, and his contributions to the field of optical manipulation will continue to have significant impact in many areas of science and engineering.”
Born Sept. 2, 1922, in Brooklyn, New York, Ashkin received his bachelor’s in physics from Columbia University in 1947. From 1942 to 1945, he worked as a technician building magnetrons at the Columbia Radiation Lab as part of the U.S. Army’s radar program.
Ashkin arrived at Cornell for graduate school at a time when the physics department in the College of Arts and Sciences also included future Nobel winners Richard Feynman and Hans Bethe, who won the prize in 1965 and ’67, respectively. Ashkin’s older brother, Julius, a nuclear physicist, had worked with Feynman and Bethe on the Manhattan Project and recommended his younger brother attend Cornell.
“His time at Cornell was transformational in many ways,” said Ashkin’s son, Michael, who is associate professor and chair of the Department of Art, in the College of Architecture, Art and Planning. “It is often mentioned that he worked with Feynman and Bethe. But he also met my mom here when she, who was an undergraduate, encountered him prospecting for fossils above the railroad tracks at Cayuga Lake.
“Being at Cornell was also the first time my dad spent any real time outside New York City, and it was here that he developed a love of nature,” he said. “When I was born a few years later, he had already bought 13 acres of wooded land in New Jersey, and it was there that he passed on to me the knowledge of trees, plants and birds that he acquired living in Ithaca.”
After graduating from Cornell, Ashkin joined the technical staff at Bell Labs in Holmdel, New Jersey, where some of the 20th century’s most important innovations, from the transistor to the first practical photovoltaic cell, were created in an effort to improve communications technology.
Ashkin started in Bell Lab’s microwave field and then moved to laser research, heading the Department of Laser Science from 1963 to 1987.
His early work addressed nonlinear optics, optical fibers and parametric oscillators, and he was part of the group that discovered the photorefractive effect, in which a laser beam passing through a crystal can temporarily alter the crystal’s optical properties. In the mid-1960s, Ashkin began to focus on the ways that radiation pressure – delivered via a highly focused laser and magnifying lens – might be able to push around miniscule particles. During an experiment in which a laser was beamed at a tiny transparent glass sphere, he found that deflected photons nudged the sphere into the beam’s center, trapping it there. Soon he was employing two beams that, when pointed at each other, could trap a tiny particle and move it.
Ashkin’s findings were published in 1970, and a year later he was using the process to levitate particles. By 1980, he had advanced these optical traps – or “tweezers” – to measure an electron’s charge. In 1987, he made the breakthrough that would eventually earn him the Nobel Prize when he used optical tweezers to capture living bacteria without damaging them.
At one point, his experiments levitating single-cell organisms, which he collected from pond scum, led a colleague to shout, “‘Oh, you got to see this – Ashkin’s trapping bugs! He’s trapping bugs!’” Ashkin recounted in a 2019 interview with Business Insider.
Ashkin retired from Bell Labs in 1992 but continued his research in his home basement, using equipment the company allowed him to take with him. In recent years, he was working on manipulating light with reflective concentrator tubes to produce cheaper, more efficient forms of solar power.
Even in retirement, Ashkin remained a familiar presence at Bell Labs. Chris Xu, the IBM Professor of Engineering, joined the technical staff at the Holmdel facility in March 1999. His office was located next to the office for retired members of the technical staff, which included Ashkin and other optics research pioneers, Jim Gordon and Gary Boyd.
“Art and I had a few conversations when we ran into each other in the hallway. He always struck me as highly insightful when talking about physics,” Xu said. “In particular, his enthusiasm was infectious, even at the age of close to 80. I still remember his excitement when he talked about the discovery of the optical trap he made many years ago. He still had the feeling of a starting grad student who just made the very first experiment work in the lab.”
That enthusiasm made for a productive career. In addition to his extensive publications, Ashkin held 47 patents; in 2013, he was inducted into the National Inventors Hall of Fame. He considered that the most important prize he ever won – at least until the Royal Swedish Academy of Sciences recognized Ashkin, along with Gérard Mourou and Donna Strickland, with the Nobel Prize in physics for their “groundbreaking inventions in the field of laser physics” in 2018.
Ashkin was the oldest winner in Nobel history, until John B. Goodenough won the Nobel Prize in chemistry at the age of 97 the following year.
For researchers like Michelle Wang, the James Gilbert White Distinguished Professor of the Physical Sciences, Ashkin’s impact continues to radiate far and wide.
“Art Ashkin’s invention of optical tweezers was truly groundbreaking, bringing optical forces to the forefront of science and enabling some of the most important advances in atomic physics, chemistry and biology. His work has inspired generations of scientists like myself,” Wang said. “With optical tweezers, we now can grab, manipulate and make precision mechanical measurements on a single cell, a single protein, or a single DNA molecule, all of which would have been science fiction not too long ago.”
Ashkin was elected to the National Academy of Engineering in 1984 and the National Academy of Sciences in 1996. He was a fellow in the Optical Society of America (OSA), the American Physical Society (APS), and the Institute of Electrical and Electronics Engineers (IEEE), and received numerous awards, including OSA’s Ives Medal/Quinn award and Townes award.
He is survived by his wife, Aline ’54; his sons, Michael and Daniel; daughter Judith ’81; five grandchildren; and two great-grandchildren.