Arthur Ashkin

Arthur Ashkin
Arthur Ashkin via video phone, December 2018
Arthur Ashkin
Born	9/2/1922
Birthplace	Brooklyn, New York, U.S.
Died	9/21/2020 Rumson, New Jersey, U.S.
Nationality	American
Occupation	Physicist
Employer	Bell Labs
Known for	Optical tweezers
Education	Ph.D., Cornell University (1952)
Awards	Nobel Prize in Physics (2018)

Arthur Ashkin (September 2, 1922 to September 21, 2020) was an American physicist who spent his entire career at Bell Laboratories. He's most famous for inventing optical tweezers, a technology that uses focused laser beams to trap and manipulate microscopic particles, atoms, molecules, and living cells. For this invention, he won the Nobel Prize in Physics in 2018, sharing it with Gérard Mourou and Donna Strickland.

At 96, Ashkin became the oldest person to ever receive a Nobel Prize, a record that stood until John B. Goodenough won the Nobel Prize in Chemistry in 2019 at age 97. Born in Brooklyn, New York, the son of Jewish immigrants, Ashkin started his work on manipulating microparticles with laser light in the late 1960s. This research led directly to his invention of optical tweezers in 1986.

His work on optical trapping changed science. It laid the groundwork for techniques now used across physics, biology, and chemistry, letting scientists study individual molecules and cells without touching them. Ashkin lived in Rumson, New Jersey, during his later years and kept working on scientific projects into his nineties.

Early Life

Arthur Ashkin was born on September 2, 1922, in Brooklyn, New York, to a family of Jewish immigrants. He spent his childhood in New York City during the interwar period. His older brother, Julius Ashkin, also pursued physics and became a noted nuclear physicist.

Published sources say little about his early childhood, but growing up in Brooklyn during the 1920s and 1930s meant living in one of America's most intellectually vibrant communities. The Ashkin household clearly supported scientific curiosity, since both Arthur and Julius ended up doing advanced work in physics.

Ashkin attended Columbia University for his undergraduate education, earning a Bachelor of Arts degree from Columbia College in 1947. His years at Columbia overlapped with the later stages of World War II and the postwar period. It was a transformative time for American physics, with rapid advances in nuclear science, radar technology, and quantum mechanics happening all around him.

Next came Cornell University for graduate studies. Ashkin earned his Ph.D. in physics there in 1952. His dissertation was titled "A measurement of positron-electron scattering and electron-electron scattering." William M. Woodward supervised the work. Cornell's physics department in the early 1950s was a leading center for experimental and theoretical physics in the United States. His training there gave him the rigorous experimental skills that would define his later career.

Education

Columbia College gave Ashkin his Bachelor of Arts in 1947. He then went to Cornell University for his doctoral studies, completing his Ph.D. in nuclear physics in 1952. His thesis focused on positron-electron and electron-electron scattering. William M. Woodward was his doctoral advisor.

The experimental nature of his dissertation showed early skill at precise laboratory measurement. That skill would prove essential later when he worked with laser light and microscopic particles. His graduate training happened nearly a decade before the laser was even invented. It wasn't until he joined industry that Ashkin redirected his attention to the optical phenomena that would make him famous.

Career

Bell Laboratories

After finishing his doctorate at Cornell, Ashkin joined Bell Laboratories, the research arm of AT&T. He'd spend his entire professional career there. Bell Labs was located in New Jersey. During the mid-twentieth century, it was one of the world's foremost industrial research institutions, responsible for everything from the transistor to information theory.

The laboratory had a strong culture of fundamental research. Major resources from AT&T meant scientists could pursue long-term investigations without immediate pressure to produce commercial results. That environment proved crucial for Ashkin's work.

At Bell Labs, Ashkin's early work focused on microwave and nonlinear optics. The laser's invention in 1960 changed everything. He was among the earliest researchers to see that laser light could manipulate matter. In the late 1960s, he began experimental work on moving microparticles using laser light. This was a period when laser technology's possibilities were still being explored across many scientific fields.

Radiation Pressure and Early Optical Trapping

Radiation pressure is the force that light exerts on objects in its path. This concept had been known since James Clerk Maxwell's time and was experimentally confirmed in the early twentieth century. But the forces were tiny. Scientists thought they were too weak to be useful. The laser changed that calculation completely.

Ashkin realized that laser light could exert enough radiation pressure to move and trap microscopic particles. He saw that light pressure could do useful work. This recognition drove much of his career. In early experiments, he showed that a focused laser beam could accelerate and trap small transparent particles, including micron-sized spheres. He identified two key components of the optical force: the gradient force, which pulls a particle toward the highest light intensity, and the scattering force, which pushes the particle in the direction the light travels.

These experiments, conducted at Bell Labs from the late 1960s onward, represented a fundamental advance in understanding light-matter interactions at microscopic scales. The idea of using light to hold and move objects without physical contact initially met skepticism from colleagues. Ashkin himself recalled it: "When I described catching living things with light people said: 'Don't exaggerate Ashkin'."

Invention of Optical Tweezers

After decades of research into optical trapping, Ashkin invented optical tweezers in 1986. The device uses a tightly focused laser beam to create a three-dimensional trap for microscopic objects. The technique relies on the optical gradient force created by a strongly focused beam of light. A laser beam focused through a high-quality microscope objective creates a steep intensity gradient near the focal point. Dielectric particles—small glass or plastic spheres, even biological cells—get pulled toward the point of highest intensity. The gradient force holds them in place, and in a sufficiently focused beam, it overcomes the scattering force that would otherwise push the particle away.

Optical tweezers broke new ground in experimental physics and biology. For the first time, scientists had a tool that could grasp, hold, and move individual microscopic objects. That included living cells and organelles. The tool used only light. The technique was nondestructive and worked in water, making it perfect for biological research.

The invention built on nearly two decades of Ashkin's work on radiation pressure and optical trapping. He refined the optical configuration. He showed that a single focused beam could create a stable three-dimensional trap. That transformed a laboratory curiosity into a practical and widely applicable scientific instrument.

Applications to Biology and Atomic Physics

One of the most important extensions of Ashkin's work was its use in biological systems. He showed that optical tweezers could trap and manipulate living cells, bacteria, and viruses without damaging them. This opened new experimental possibilities. Researchers could now study the mechanical properties of individual cells, measure the forces generated by molecular motors, and investigate the behavior of single DNA molecules and other biological macromolecules.

Ashkin also pioneered optical trapping of atoms. His work on atom trapping influenced the development of techniques that others, including Steven Chu, later refined. Chu shared the 1997 Nobel Prize in Physics for developing methods to cool and trap atoms with laser light. Looking at the path from Ashkin's early optical trapping experiments to the broader field of laser cooling and atom trapping shows how foundational his contributions were.

Optical tweezers have found more and more uses since their invention. In physics, they've tested predictions of statistical mechanics and measured Brownian motion of trapped particles with high precision. Researchers use them to study colloids and polymers. In chemistry, they've enabled the study of single-molecule reactions. In biology and medicine, optical tweezers became standard tools for single-molecule biophysics. They let researchers measure forces from individual motor proteins, stretch DNA molecules, and probe the mechanical properties of cell membranes. The breadth of these applications shows how general the underlying principle was.

Later Career and Continued Research

Ashkin stayed scientifically active long after retiring from Bell Labs. He continued working on scientific problems, including research on solar energy, well into his nineties. His sustained engagement with research across more than fifty years showed his intellectual curiosity and commitment to science.

When the Nobel Prize was announced in October 2018, Ashkin was 96 years old. His advanced age meant he couldn't travel to Stockholm for the ceremony. His Nobel Lecture was delivered on his behalf by René-Jean Essiambre of Nokia Bell Labs on December 8, 2018, at the Aula Magna, Stockholm University.

Personal Life

Arthur Ashkin spent much of his adult life in Rumson, New Jersey. His parents were Jewish immigrants to the United States. His older brother, Julius Ashkin, was a physicist who contributed to nuclear physics research.

Colleagues knew Ashkin for his directness and persistence in pursuing scientific questions. His decades-long investigation of radiation pressure and optical trapping, from late 1960s experiments through the 1986 invention of optical tweezers and beyond, reflected sustained commitment to a research path that wasn't always seen as significant by the broader scientific community early on.

Arthur Ashkin died on September 21, 2020, at his home in Rumson, New Jersey, at the age of 98.

Recognition

The Nobel Prize in Physics stood as Ashkin's most prominent recognition. He received it in 2018 "for the optical tweezers and their application to biological systems." Gérard Mourou and Donna Strickland shared the prize. They were recognized for their method of generating high-intensity, ultra-short optical pulses. Ashkin received one half of the prize. Mourou and Strickland shared the other half.

At 96, Ashkin was the oldest person ever to receive a Nobel Prize. He surpassed the previous record held by Leonid Hurwicz, who had received the Nobel Memorial Prize in Economic Sciences in 2007 at age 90. But his record didn't stand long. In 2019, John B. Goodenough received the Nobel Prize in Chemistry at age 97.

Ashkin was elected to the National Academy of Sciences, one of the highest honors for an American scientist. He also served as a member of the National Academy of Engineering.

The Optical Society of America (OSA) gave Ashkin additional honors, recognizing his contributions to optics. LaserFest, a celebration of the 50th anniversary of the laser organized by the American Physical Society, the Optical Society of America, and other scientific organizations, also recognized him as a pioneer in laser science.

International media covered Ashkin's Nobel Prize announcement extensively. The Guardian reported it, as did the Times of Israel, and Physics World.

Legacy

Arthur Ashkin's invention of optical tweezers transformed experimental practice across many scientific disciplines. The technology he developed enabled a new class of experiments. Scientists could now hold, move, and study individual microscopic objects using focused laser light, with no physical contact. This capability became essential in fields ranging from fundamental physics to molecular biology.

In physics, optical tweezers tested predictions of statistical mechanics. They measured the Brownian motion of trapped particles with high precision. They let researchers study colloids and polymers. In biology, they became indispensable for single-molecule biophysics. Researchers could measure the forces generated by individual motor proteins, stretch and manipulate DNA molecules, and probe the mechanical properties of cell membranes. Ashkin's techniques contributed directly to the emergence of single-molecule biology as a distinct scientific field in the 1990s and 2000s.

His early work on optical trapping of atoms also shaped the development of laser cooling and atom trapping. These techniques have now become central to atomic physics and quantum information science. Steven Chu, who worked with Ashkin at Bell Labs before winning the 1997 Nobel Prize in Physics for laser cooling, acknowledged Ashkin's foundational contributions to the field.

The impact of Ashkin's work appears in thousands of scientific publications that have used or built upon optical tweezers since 1986. He showed that radiation pressure, a phenomenon known for over a century but considered impractical, could be harnessed as a precise and versatile tool for scientific investigation. The description of Ashkin as the "father of optical tweezers" appears in multiple scientific publications and obituaries, reflecting scientific consensus about his central role in developing the technology.

His career also exemplified the productive relationship between fundamental research and practical application at Bell Laboratories during the mid-to-late twentieth century. His ability to pursue a single research line for nearly two decades before getting his most significant result depended on institutional support for long-term basic research that Bell Labs provided.