2020-10-01 20:59:40 UTC
Arthur Ashkin, 98, Dies; Nobel Laureate Invented a ‘Tractor Beam’
By Dylan McClain, 9/28/20, New York Times
Arthur Ashkin, a physicist who was awarded a 2018 Nobel Prize for
figuring out how to harness the power of light to trap microscopic
objects for closer study, calling his invention optical tweezers, died on
Sept. 21 at his home in Rumson, N.J. He was 98.
His daughter, Judith Herscu, confirmed the death on Monday.
Optical tweezers — or optical traps, as they are more properly known —
use the pressure from a highly focused laser beam to manipulate
microscopic objects, from atoms to living organisms, like viruses &
As the Nobel committee wrote, Dr. Ashkin had “invented optical tweezers
that grab particles, atoms, molecules, & living cells with their laser
Trapping bio material proved to have groundbreaking practical apps in
research & in understanding the behavior of the basic building blocks of
life, like DNA, & other bio systems. Today, optical tweezers are widely
manufactured & sold to researchers.
Dr. Ashkin’s “tweezer” is created by shining a laser — a beam of coherent
monochromatic light — thru a tiny magnifying lens. The lens creates a
focal point for the laser, &, by a strange twist of nature, particles are
drawn near that focal point & trapped there, unable to move up or down or
backward or forward.
Steven M. Block, a prof of biology & applied physics at Stanford,
compared optical tweezers to the kind of immobilizing tech postulated in
“Star Trek” & “Star Wars,” calling them “the closest thing to a tractor
beam that humans have ever produced.”
Dr. Ashkin’s discovery was serendipitous.
In 1966, he was head of the laser research dept at Bell Labs, the storied
New Jersey lab founded by the Bell Telephone Co in 1925, when he went to
a scientific conference in Phoenix. There, in a lecture, he heard two
researchers discuss something odd that they had found while studying
lasers, which had been invented 6 years earlier: They had noticed that
dust particles within the laser beams careened back & forth. They
theorized that light pressure might be the cause.
Dr. Ashkin did some calcs & concluded that this was not the cause — it
was most likely thermal radiation. But his work reignited a childhood
interest in the subject of light pressure.
Light pushes against everything, including people, because it comprises
tiny particles called photons. Most of the time the pressure is utterly
insignificant; people, for one, feel nothing. But Dr. Ashkin thought that
if objects were small enough, a laser might be used to push them around.
He experimented with a tiny transparent glass sphere thru which the
photons of the laser could pass, & found that he was indeed able to push
it around. But unexpectedly the sphere gravitated toward the center of
the beam, where it became trapped.
The reason had to do with one of the immutable laws of physics: the
conservation of momentum. As the photons passed thru the sphere & were
deflected by it, the sphere moved in the opposite direction of the
deflected photons. Since there were more photons at the center of the
beam, the sphere was driven toward the center.
Dr. Ashkin realized that by using two beams pointed at each other, it
would be possible to trap tiny objects & move them around. A landmark
article about his discovery was published in Physical Review Letters in
Dr. Ashkin continued to research the subject along with his colleagues at
Bell Labs, & in 1980 he came up with a way to use optical traps to
measure the charge of an electron.
Then, in 1986, he & several colleagues, notably Steven Chu, achieved the
first practical app of optical tweezers when they sent a laser thru a
lens to manipulate micro objects. Their results were published in another
paper in Physical Review Letters. Dr. Chu began using the tweezers to
cool & trap atoms, a breakthru for which he was awarded a 1/3 share of
the Nobel Prize in Physics in 1997.
Dr. Ashkin, it was clear, was irked that the Nobel committee had not
recognized his foundational work in awarding the prize. But he had
already begun to use the tweezers for a different purpose: trapping live
organisms & biological material.
Other scientists thought this app would not work, as he explained in an
interview with the Nobel Institute after he was awarded the prize in
“They used light to heal wounds, & it was considered to be deadly,” he
said. “When I described catching living things with light, people said,
‘Don’t exaggerate, Ashkin.’”
Among the things Dr. Ashkin was able to trap were subcellular structures
of the single-celled paramecium & a small virus that attacks tobacco
plants. Through his trapping method it also became possible to observe
DNA being replicated.
Dr. Ashkin was awarded one-half the 2018 physics prize, sharing it with
Gérard Mourou of France & Donna Strickland of Canada, who each received a
quarter of it. In so doing he became, at 96, the oldest recipient of a
Nobel at the time. (The next year, John B. Goodenough received the Nobel
in chemistry at 97.)
Unable to attend the Nobel ceremony in Stockholm, Dr. Ashkin delivered
his Nobel lecture from the Nokia Bell Labs in New Jersey.
Arthur Ashkin was born on Sept. 2, 1922, in Brooklyn, one of four
children of Isadore & Anna Ashkin, who were of Ukrainian-Jewish heritage.
His older brother, Julius, also became a physicist & played an important
role in the Manhattan Project, the secret effort during WWII to develop
the atomic bomb.
After graduating from James Madison H.S., Arthur followed Julius to
Columbia Univ. He worked in the Columbia Radiation Lab on magnetrons,
which produced microwaves & were a precursor to the laser. Two other
future Nobel laureates were working in the lab at the time.
Dr. Ashkin graduated from Columbia in 1947 & studied nuclear physics at
Cornell, where he worked with Hans Bethe & Richard Feynman, both future
Nobel laureates as well. He joined Bell Labs after obtaining his Ph.D.
from Cornell in 1952 & worked there until his retirement in 1992. He led
the lab’s laser science dept from 1963-87.
In addition to optical tweezers, Dr. Ashkin was credited with discovering
the photorefractive effect, which temporarily alters how materials,
notably crystals, scatter or bend light. The practical uses of the effect
include creating temporary holograms. Scientists believe that it could
lead to more powerful computers that would use light, rather than
electricity, to store data.
Dr. Ashkin held 47 patents & was inducted into the National Inventors
Hall of Fame in 2013.
In addition to his daughter, Judith, he is survived by his wife, Aline
Ashkin, a former H.S. chemistry prof who taught many of the children of
Bell Labs employees; their sons, Daniel & Michael, an artist whose work
has appeared in biennials at the Whitney Museum of American Art in NY; 5
grandkids; & 2 great-grandkids.
Dr. Ashkin’s retirement from Bell Labs did not stop him from continuing
his research. When he received word of his Nobel Prize, he was working on
a project in his basement to improve solar energy collection. Asked if he
was going to celebrate, he said: “I am writing a paper right now. I am
not about celebrating old stuff.”