Arthur Ashkin

Arthur Ashkin
Arthur Ashkin via video phone, December 2018
Arthur Ashkin
Born	2 9, 1922
Birthplace	Brooklyn, New York, U.S.
Died	Template:Death date and age 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 – September 21, 2020) was an American physicist who spent the majority of his career at Bell Laboratories and became known as the inventor of optical tweezers — a technology that uses focused laser beams to trap and manipulate microscopic particles, atoms, molecules, and living cells. For this invention, he was awarded the Nobel Prize in Physics in 2018, sharing it with Gérard Mourou and Donna Strickland. At the age of 96, Ashkin became the oldest person to receive a Nobel Prize at the time of his award, a record that stood until John B. Goodenough received the Nobel Prize in Chemistry in 2019 at the age of 97. Born in Brooklyn, New York, the son of Jewish immigrants, Ashkin began his pioneering work on the manipulation of microparticles with laser light in the late 1960s, a line of research that culminated in the invention of optical tweezers in 1986. His work on optical trapping laid the groundwork for techniques used across physics, biology, and chemistry, enabling scientists to study individual molecules and cells without physical contact. He resided in Rumson, New Jersey, for much of his later life and continued working on scientific projects well into his nineties.

Early Life

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

Details of Ashkin's early childhood remain limited in published sources, but his upbringing in Brooklyn during the 1920s and 1930s placed him in one of the most intellectually vibrant communities in the United States. The Ashkin household evidently fostered scientific curiosity, as both Arthur and his brother Julius went on to pursue advanced studies in physics.

Ashkin attended Columbia University in New York City for his undergraduate education, graduating with a Bachelor of Arts degree from Columbia College in 1947. His time at Columbia would have coincided with the later years of World War II and the immediate postwar period, a transformative era in American physics that saw rapid advances in nuclear science, radar technology, and quantum mechanics.

After completing his undergraduate degree at Columbia, Ashkin pursued graduate studies at Cornell University, where he earned his Ph.D. in physics in 1952. His doctoral dissertation, titled "A measurement of positron-electron scattering and electron-electron scattering," was completed under the supervision of William M. Woodward. Cornell's physics department in the early 1950s was a leading center for experimental and theoretical physics in the United States, and Ashkin's training there equipped him with the rigorous experimental skills that would define his subsequent career.

Education

Ashkin's formal education spanned two of the most prominent institutions in American higher education. He received his Bachelor of Arts from Columbia College, Columbia University, in 1947. He then enrolled at Cornell University for his doctoral studies, completing his Ph.D. in nuclear physics in 1952 with a thesis on positron-electron and electron-electron scattering. His doctoral advisor was William M. Woodward. The experimental focus of his dissertation — measuring fundamental particle interactions — demonstrated an early aptitude for precise laboratory measurement, a skill that would prove essential in his later work with laser light and microscopic particles. His graduate training at Cornell preceded the invention of the laser by nearly a decade, and it was only after joining industry that Ashkin would redirect his attention to the optical phenomena that made his reputation.

Career

Bell Laboratories

Following his doctoral work at Cornell, Ashkin joined Bell Laboratories, the research arm of AT&T, where he would spend the entirety of his professional career. Bell Labs, located in New Jersey, was during the mid-twentieth century one of the foremost industrial research institutions in the world, responsible for innovations ranging from the transistor to information theory. The laboratory's culture of fundamental research, supported by the resources of a major telecommunications company, provided an environment in which scientists could pursue long-term investigations without immediate commercial pressure.

At Bell Labs, Ashkin initially worked on microwave and nonlinear optics research. The invention of the laser in 1960 opened new avenues of investigation, and Ashkin was among the earliest researchers to recognize the potential of laser light for manipulating matter. He began his experimental work on the manipulation of microparticles using laser light in the late 1960s, a period during which the possibilities of laser technology were still being explored across multiple scientific disciplines.

Radiation Pressure and Early Optical Trapping

The foundational principle underlying Ashkin's most significant work was radiation pressure — the force exerted by light on objects in its path. Although the concept of radiation pressure had been known since the time of James Clerk Maxwell and had been experimentally confirmed in the early twentieth century, the forces involved were extremely small and had been considered too weak to be of practical use. The advent of the laser, with its ability to produce intense, coherent beams of light, changed this calculation fundamentally.

Ashkin recognized that laser light could exert sufficient radiation pressure to move and trap microscopic particles. He foresaw that light pressure could do useful work and dedicated much of his career to demonstrating and exploiting this phenomenon. In his early experiments, Ashkin demonstrated that a focused laser beam could accelerate and trap small transparent particles, including micron-sized spheres. He identified and characterized two key components of the optical force: the gradient force, which pulls a particle toward the region of highest light intensity, and the scattering force, which pushes the particle in the direction of light propagation.

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

Invention of Optical Tweezers

Ashkin's decades of research into optical trapping culminated in 1986 with the invention of optical tweezers, a device that uses a tightly focused laser beam to create a three-dimensional trap for microscopic objects. The optical tweezers technique relies on the optical gradient force produced by a strongly focused beam of light. When a laser beam is focused through a high-quality microscope objective, it creates a steep intensity gradient near the focal point. Dielectric particles — such as small glass or plastic spheres, and even biological cells — are drawn toward the point of highest intensity and held in place by the gradient force, which in a sufficiently focused beam overcomes the scattering force that would otherwise push the particle away.

The development of optical tweezers represented a breakthrough in experimental physics and biology. For the first time, scientists had a tool that could grasp, hold, and move individual microscopic objects — including living cells and organelles — using nothing but light. The technique was nondestructive and could be applied in aqueous environments, making it suitable for biological research.

The invention built upon nearly two decades of Ashkin's prior work on radiation pressure and optical trapping. By refining the optical configuration and demonstrating that a single focused beam could create a stable three-dimensional trap, Ashkin transformed what had been a laboratory curiosity into a practical and widely applicable scientific instrument.

Applications to Biology and Atomic Physics

One of the most significant extensions of Ashkin's work was its application to biological systems. Ashkin demonstrated that optical tweezers could be used to trap and manipulate living cells, bacteria, and viruses without damaging them. This capability opened new experimental possibilities in cell biology, allowing researchers to study the mechanical properties of individual cells, measure the forces generated by molecular motors, and investigate the behavior of single molecules of DNA and other biological macromolecules.

Ashkin also pioneered the optical trapping of atoms. His work on atom trapping contributed to the development of techniques that were later refined by other physicists, including Steven Chu, who shared the 1997 Nobel Prize in Physics for the development of methods to cool and trap atoms with laser light. The lineage from Ashkin's early optical trapping experiments to the broader field of laser cooling and atom trapping illustrates the foundational nature of his contributions.

The applications of optical tweezers have expanded continually since their invention. In physics, they have been used to test fundamental theories of statistical mechanics and to measure forces at the piconewton scale. In chemistry, they have enabled the study of single-molecule reactions. In biology and medicine, optical tweezers have become standard tools for investigating cellular mechanics, protein folding, and the dynamics of molecular motors such as kinesin and myosin. The breadth of these applications reflects the generality of the underlying principle that Ashkin identified and developed.

Later Career and Continued Research

Ashkin remained scientifically active long after his formal retirement from Bell Labs. He continued to work on scientific problems, including research on solar energy, well into his nineties. His sustained engagement with research over more than half a century was a testament to his intellectual curiosity and commitment to scientific investigation.

When the Nobel Prize was announced in October 2018, Ashkin was 96 years old. He was unable to travel to Stockholm for the award ceremony due to his advanced age. His Nobel Lecture was instead 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 resided in Rumson, New Jersey, for much of his adult life. He was the son of Jewish immigrants to the United States. His older brother, Julius Ashkin, was a physicist who contributed to nuclear physics research.

Ashkin was known among colleagues for his directness and persistence in pursuing scientific questions. His decades-long investigation of radiation pressure and optical trapping, from his initial experiments in the late 1960s through the invention of optical tweezers in 1986 and beyond, reflected a sustained commitment to a line of research that was not always recognized as significant by the broader scientific community during its early stages.

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

Recognition

Arthur Ashkin's most prominent recognition was the Nobel Prize in Physics, which he received in 2018 for "the optical tweezers and their application to biological systems." He shared the prize with Gérard Mourou and Donna Strickland, who were recognized for their method of generating high-intensity, ultra-short optical pulses. Ashkin received one half of the prize, while Mourou and Strickland shared the other half.

At 96 years of age at the time of the award, Ashkin was the oldest person ever to receive a Nobel Prize, surpassing the previous record held by Leonid Hurwicz, who had received the Nobel Memorial Prize in Economic Sciences in 2007 at the age of 90. Ashkin's record was subsequently surpassed in 2019 by John B. Goodenough, who received the Nobel Prize in Chemistry at the age of 97.

Ashkin was elected a member of the National Academy of Sciences, one of the highest honors for a scientist in the United States. He was also a member of the National Academy of Engineering.

Ashkin received additional honors from the Optical Society of America (OSA), which recognized his contributions to the field of optics. He was also recognized as a pioneer in laser science by the LaserFest initiative, a celebration of the 50th anniversary of the laser organized by the American Physical Society, the Optical Society of America, and other scientific organizations.

The announcement of Ashkin's Nobel Prize was covered extensively by international media, including The Guardian, the Times of Israel, and Physics World.

Legacy

Arthur Ashkin's invention of optical tweezers transformed experimental practice across multiple scientific disciplines. The technology he developed enabled a new class of experiments in which individual microscopic objects could be held, moved, and studied using focused laser light, without any physical contact. This capability proved essential in fields ranging from fundamental physics to molecular biology.

In physics, optical tweezers have been used to test predictions of statistical mechanics, to measure the Brownian motion of trapped particles with high precision, and to study the properties of colloids and polymers. In biology, they have become indispensable tools for single-molecule biophysics, allowing researchers to measure the forces generated by individual motor proteins, to stretch and manipulate DNA molecules, and to probe the mechanical properties of cell membranes. The techniques developed by Ashkin contributed directly to the emergence of single-molecule biology as a distinct scientific field in the 1990s and 2000s.

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

The breadth of Ashkin's influence is reflected in the thousands of scientific publications that have employed or built upon optical tweezers since their invention in 1986. His work demonstrated 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 designation of Ashkin as the "father of optical tweezers" has appeared in multiple scientific publications and obituaries, reflecting the consensus within the scientific community regarding his central role in developing the technology.

Ashkin's career also exemplified the productive relationship between fundamental research and practical application that characterized Bell Laboratories during the mid-to-late twentieth century. His ability to pursue a line of research for nearly two decades before it yielded its most significant result — the optical tweezers — was enabled by the institutional support for long-term basic research that Bell Labs provided.