Light is the primary way we gather information about the world, and every breakthrough in light manipulation lets researchers see new aspects of nature in new ways. Today, three scientists shared the Nobel Prize in Physics for their work developing powerful laser technology that has allowed biologists and physicists to lift the veil hiding the very small, and the very fast.
The award honors the inventors of two influential laser tools: Arthur Ashkin, an American physicist, for developing a way to catch and hold objects using focused beams of light, and Gérard Mourou of France and Donna Strickland of Canada, for their creative solution for concentrating and amplifying laser beams beyond what standard materials would permit. Strickland, an associate professor at Waterloo University in Canada, is the third woman to win a Nobel Prize in Physics, after Marie Curie in 1903 and Maria Goeppert-Mayer in 1963.
“Obviously, we need to celebrate women physicists, because we’re out there,” she said, according to NPR. “I don’t know what to say, I’m honored to be one of these women.”
Ashkin invented a real-life version of the tractor beam device from Star Trek, understatedly dubbed “optical tweezers.” While working at Bell Labs in the 1960s and 1970s, he confirmed conventional wisdom dating back to the 1600s that beams of light could push matter, even if only a little. “Light doesn’t pack that much of a punch,” says David Grier, a physicist who works with optical traps at New York University. “You’re not going to be lifting a truck, but you could imagine moving an atom.”
Atoms are hard to see, so Ashkin started with clear microscopic beads. Right off the bat, he noticed that in addition to moving “downstream,” the particles were also drifting toward the middle, more intense region of the beam. The next logical step was to see how fast he could move particles, so he set up a lens to concentrate the beam to a point. He imagined that nearby particles would get dragged into the center of the beam and then shot out by the magnified downstream force, “like an optical cannon,” Grier says.
But that’s not what happened. Instead, the particles flew to the central point and froze, trapped in place. By moving the beam back and forth, Ashkin could move these tiny particles around too, hence the name optical tweezers. No one had suspected that a wave could pull an object upstream against the flow of the laser, but it didn’t take long to figure out the reason. When the clear beads scattered light downstream, they naturally recoiled backward, like a canoer heaving a bowling ball over the bow. “It overturned a century of intuition,” Grier says. “It was something that was there the whole time in plain sight, and Art realized it.”
Ashkin soon graduated from tweezing beads to live bacteria and viruses, which has proved invaluable for biologists since, you know, there aren’t too many ways to pick up critters that tiny. Other scientists recognized the tool’s value almost instantly, according to Grier, and researchers around the world were using optical traps within a couple of years.
Today physicists continue to expand the technique’s capabilities. While Ashkin’s tweezers could move just one object per laser, Grier’s lab pioneered a way to expand one beam with a computer-generated image and then focus it down to trap hundreds of particles at once. They’re currently partnering with NASA to scale up the technology and snag ancient ice crystals and dust particles that passing comets may have conveniently deposited in Earth’s orbit, some of which you can see with the naked eye. “That’s actually kind of eerie,” he says, “when you have something big enough to see floating around on a cushion of light.”
The other half of the prize is split by Strickland, and Mourou, currently at École Polytechnique in France, who answered a longstanding prayer of laser-wielding experimentalists: more power. After the invention of the first laser in 1960, physicists steadily reached higher intensity levels for about a decade until they hit a wall.
Lasers first produce weak pulses of light using a device called an oscillator and then amplify them, shockingly enough, with an amplifier. But after a certain point, the amplified light gets too intense and destroys the device like the sound waves from a speaker cranked up to 11. To avoid this meltdown, Mourou and Strickland, who were working together at the University of Rochester at the time, hit on a clever solution—stretch the beam out (they used a fiber optic cable nearly a mile long), amplify it in its weakened form, and then re-compress it to get a super short, super powerful “pulse.” After working out the kinks they published the work in 1985, jump-starting a race toward better, faster, stronger laser pulses that even today shows no signs of slowing down.
“This is one of the biggest revolutions in optical science,” says Zenghu Chang, an optical physicist at the University of Central Florida whose lab demonstrated a record-breakingly short laser pulse last year. “It’s an invention that leads to discoveries.”
Known as chirped pulse amplification (CPA), these unimaginably short and powerful flashes launched multiple fields of experimental physics and opened the door to what Chang calls “extreme science.” The intense heat and magnetic fields the lasers produce let researchers study matter under exotic conditions, create plasma, and hurl off electrons at nearly the speed of light. On the more practical side, with enough intensity you can boil whatever material the laser hits, producing a rapid evaporation that manufacturers use to cut metals with fine precision. Doctors also use this technology to improve the vision of millions of people a year with corrective eye surgery.
The superlative speed of CPA lasers also opened up a whole new realm of fast phenomena to scientific imaging. “When you want to see something fast, you need to use something even faster,” Chang says. His record-breaking 2017 flash, which uses a CPA laser kind of like a spark plug, lasted just 53 attoseconds. (In one second, light can get almost from the Earth to the Moon. In an attosecond, it can traverse just one or two atoms.) Pulses this brief make it possible to capture images and videos of molecules and electrons.
The Nobel Prize in Physics usually highlights advances in fundamental physics, but past recognitions of technology include the inventors of the radio transmitter (1909), the transistor (1956), the OG laser (1964), the semiconductor (2000) and the LED (2014).
This 2018 award adds another entry to the exclusive list of Nobel-Prize-winning technology, but for the thousands of researchers who use the tools Ashkin, Mourou, and Strickland invented and work in the optical fields their research spawned, the nod is long overdue.
“I’ve been waiting for this news for a long time,” Chang says. “We knew this was going to happen someday.”
This post has been updated.
