L - Ashkin at Bell Labs in 1988 with a monitor behind him showing medical imagery. C - Strickland. R - Mourou holding microphone

Arthur Ashkin, Donna Strickland and Gérard Mourou.L-R: Nokia Bell Labs; Univ. Waterloo; CTK/Alamy

A trio of laser scientists has won the 2018 Nobel Prize in Physics for work using intense beams to capture superfast processes and to manipulate tiny objects. The laureates include Donna Strickland, who is the first woman to win the award in 55 years.

Strickland, at the University of Waterloo, Canada, shares half of the prize, worth 9 million Swedish krona (US$1 million), with her former supervisor, Gérard Mourou, now at the École Polytechnique in Paris. Arthur Ashkin of Bell Laboratories in Holmdel, New Jersey, won the other half of the prize.

Strickland and Mourou pioneered a way to produce the shortest, most-intense pulses of light ever created. The technique is now used throughout science to unravel processes that previously seemed instantaneous, such as the motion of electrons in atoms, as well as in laser eye surgery.

Ashkin won the prize for his pioneering development of ‘optical tweezers’, beams of laser light that can grab and control microscopic objects such as viruses and cells.

“First of all, you have to think it’s crazy, so that was my first thought,” said Strickland, during the announcement of the prizes on 2 October. “And you do always wonder if it’s real.”

Pioneering work

According to a statement released by the Royal Swedish Academy of Sciences, which awards the prize, the applications of the laureates' work have not yet been completely explored. “However, even now these celebrated inventions allow us to rummage around in the microworld in the best spirit of Alfred Nobel — for the greatest benefit to humankind.”

Strickland is the third woman ever to win the Nobel Prize in Physics; the last female scientist to win was Maria Goeppert Mayer in 1963.

“I thought there might have been more,” said Strickland when asked about this aspect of the achievement. She added: “Well obviously we need to celebrate women physicists because we’re out there, and hopefully in time, it will start to move forward at a faster rate maybe. I don’t know what to say, I’m honoured to be one of those women.”

Göran K. Hansson, secretary-general of the Royal Swedish Academy of Sciences, said that the academy is “taking measures” to encourage more nominations of female scientists “because we don’t want to miss anyone”. He added that those measures did not affect this year’s prize. “It’s important to remember that the Nobel prize is awarded for discoveries and inventions, and those who receive it have made major contributions to humankind, and that’s why they get the prize.”

Stretched in time

Short-lived laser pulses allow scientists to spy on processes that are over in a heartbeat. But before Strickland and Mourou’s revolutionary technique, the intensity of such laser pulses was limited because the high power risked destroying the amplifier needed to create them.

Their breakthrough was to use a grating to stretch out a laser beam pulse in time. This reduces the power of light and means that conventional amplifiers can be used, before the pulse is squeezed back together into a short, powerful blast — a process known as chirped pulse amplification.

Originally outlined in a 1985 article1 that Strickland wrote as a PhD student — her first ever scientific paper — improvements to the technique now allow scientists to generate laser pulses on the scale of attoseconds — billionths of a billionth of a second. Like a video camera taking ever more frames per second, these pulses can be used to study rapidly evolving processes such as the chemistry of photosynthesis. Moreover as fleeting pulses cause less damage than longer ones, ultra-short light pulses have found uses not just in laser eye surgery, but also in drilling ever-sharper holes in data-storage materials to allow for more-efficient memories.

John Dudley, an optical physicist at the University of Franche-Comté in Besançon, France, says that Strickland and Mourou’s chirped pulse amplification was a breakthrough both as a basic science advance and as a technological development. “Nobels are awarded for a discovery or an invention. This really bridges the two.”

Dudley adds neither of the scientists "remained in their ivory towers”. He notes that Mourou, in particular, has been the driving force for the Extreme Light Infrastructure, a European consortium that investigates light at high intensities and short timescales.

He adds that Mourou is a polymath who composes music and has a broad interest in the humanities.

Dudley says that it’s particularly significant that Strickland was recognized for work she did as a graduate student. This contrasts with the case of Jocelyn Bell Burnell, the British astrophysicist who discovered pulsars but who was passed over when her adviser shared the 1974 Nobel prize. “It’s wonderful to see that the Nobel committee has listened to the community and to the negative reaction to that decision at the time,” Dudley says.

Microscale fingers

At 96, Ashkin is the oldest-ever Nobel laureate. His prizewinning work began immediately after the laser’s invention in 1960. Lasers exert a gentle pressure on tiny objects, which Ashkin realized could be used to manipulate them without damaging them. His experiments with micrometre-sized spheres in the 1960s showed that the particles were drawn to the highest-intensity region in a beam of light. This led to a way to sculpt laser beams to trap, levitate and move objects. Now known as optical tweezers, Ashkin discovered that these highly focused laser ‘fingers’ could capture bacteria, viruses and living cells.

“I’m absolutely ecstatic for him. He’s such a nice guy,” says Miles Padgett, an optical physicist at the University of Glasgow, UK.

He says that Ashkin’s invention has had a universally recognized impact, and especially in biophysics. Today, optical tweezers are used in myriad applications, from separating healthy blood cells from infected ones to engineering nanoscale materials.

Padgett applauds how Ashkin kept improving the technique and making the devices simpler. “I think it’s wonderful when people plough through. He just kept on making it better and better.”

He and many others in the optical-tweezer community had assumed that Ashkin had been sidestepped in 1997, when Steven Chu shared the Nobel in Physics for a related technique. “I thought he’d missed his chance, so to speak.”