This Nobel Laureate Paved the Way for High-Intensity Lasers
Growing up, Donna Strickland had one goal in mind: Earn a Ph.D. But she didn’t know what subject she wanted to pursue until she began her undergraduate studies in physics at McMaster University, in Hamilton, Ont., Canada. It was there that she got interested in studying lasers after taking a course on the subject.
The topic seemed “really cool—like something from a science-fiction novel,” Strickland says. Little did she know that her newfound passion would one day earn her a Nobel Prize in physics.
University of Waterloo, in Ontario
University of Rochester, in New York
While conducting research in optics for her doctorate at the University of Rochester, in New York, Strickland worked with French physicist Gérard Mourou, a laser pioneer and Nobel laureate. Mourou led the development of the Extreme Light Infrastructure network of physics laboratories built to generate and study intense laser light. Together, while experimenting with how to increase a laser’s peak power without damaging it, they invented the chirped-pulse amplification technique. CPA, which produces short laser pulses that reach high intensity, now is used in corrective eye surgery, medical imaging, smartphone manufacturing, and many more applications.
Strickland and Mourou shared the 2018 Nobel Prize in physics with IEEE Life Fellow Arthur Ashkin, who invented a separate technology: “optical tweezers,” which use low-power laser beams to manipulate living cells and other tiny objects.
Receiving the Nobel was “life-changing,” Strickland says, adding, “Your life can change in a single day without you being ready for it.”
“Donna’s work has been transformative. Her seminal research on chirped-pulse amplification is the gold standard of research,” one of her award endorsers said. “Additionally, she is a true role model to legions of engineers around the world. She is an extremely giving person and a shining example of what an IEEE honorary member should be.”
Strickland is a physics professor at the University of Waterloo, in Ontario, where she leads a group of researchers that is developing high-intensity laser systems for nonlinear optics investigations such as generating midinfrared pulses by difference frequency mixing and studying the multifrequency Raman generation technique.
Donna Strickland receives the 2018 Nobel Prize in physics from King Carl Gustaf of Sweden, at the Stockholm Concert Hall.Henrik Montgomery/TT News Agency/Getty Images
Paving the way for high-intensity lasers
After graduating in 1981 with a bachelor’s engineering degree in physics from McMaster, Strickland moved to New York to pursue a doctorate in optics at the University of Rochester, which at the time was considered one of the top schools for studying laser optics. She joined Mourou at the university’s Laboratory for Laser Energetics, where he was looking for ways to increase lasers’ intensity (its optical power) without damaging the device.
Pulsed lasers can concentrate light onto a small area for a short time to produce power. Peak intensities increased rapidly for several years after physicist Theodore Maiman demonstrated the first laser in 1960. But the intensities plateaued for more than a decade after 1970 because amplifying the light past a certain point damaged the laser.
In his research on how light interacts with matter, Mourou hypothesized in 1983 that spacing out and augmenting pulses before bringing them back together could result in higher-intensity laser pulses without damage. But he didn’t know how to accomplish it, Strickland says. So for her doctoral research, she tested his hypothesis with different laser systems. None of her experiments worked, however.
“Donna is a true role model to legions of engineers around the world. She is an extremely giving person and a shining example of what an IEEE honorary member should be.”
It wasn’t until Strickland and Mourou attended the 1984 International Conference on Ultrafast Phenomena that they found the solution. The biannual event brings together scientists who are developing tools, methodologies, and techniques used to study processes in atoms, molecules, or materials that occur in millionths of a billionth of a second or faster.
Strickland and Mourou attended a presentation at the conference about the newly developed optical fiber pulse compression of neodymium-doped yttrium aluminum garnet (Nd:YAG) lasers. With the technique, 100-picosecond pulses could be compressed to 1 ps using nonlinear optics in an optical fiber to increase a laser’s spectral bandwidth. It was found that compression was most successful when the pulses were allowed to stretch through dispersion in the fiber.
“I was using those same lasers for my experiments,” Strickland recalled.
She and Mourou figured out how she could safely create the high-intensity pulse: The pulse needed to be stretched before it was amplified rather than afterward, as what had been done. Stretching the pulse meant it could be recompressed to produce the desired intensity.
To test her theory, Stickland and Mourou built a system at the Laboratory for Laser Energetics that was composed of a 2-watt Nd:YAG laser, 1.4 kilometers of optical fiber, an amplifier, and a pair of parallel gratings.
The Nd:YAG laser pumped a short pulse at 100 ps into the optical fiber. As the velocity of light is dependent on wavelength, the red component of the light propagates faster than the blue within the fiber.
That is referred to as a “chirped pulse,” Strickland says, because a bird’s chirp has a similar frequency structure.
The chirped pulse makes the duration of the pulse longer and spreads out the intensity so that it doesn’t damage the laser. The stretched, lower-energy density pulse was then amplified and passed through a pair of parallel diffraction gratings—which allowed the trailing blue component to catch up to the red. Both were reassembled by reflecting off the gratings. The reassembled pulse was three times more powerful than the original one, Stickland says.
The technique, which was named after the chirped pulse, has since paved the way for the shortest and most intense laser pulses ever created, making it possible to build more compact and precise laser systems.
From Princeton to Waterloo
After helping develop CPA, Strickland still wasn’t sure what career path to pursue. She sought advice from her colleagues, and one told her that Paul Corkum, a physicist who worked in the Canadian National Research Council’s ultrafast-phenomena department, was getting his first postdoctoral research fellow that year. Corkum, who specialized in laser science, pioneered the development of attosecond physics. Strickland liked the sound of that.
“I remember telling the other doctoral candidates in my research lab that Corkum may not know my name yet, but I was going to be his second postdoc,” she says. She got her dream job in 1988 and worked for him for three years.
While she lived on the West Coast, her husband, a physicist, lived on the East Coast, working at Bell Labs in Murray Hill, N.J.
After spending a year apart, Strickland moved to New Jersey to join the technical staff at Princeton’s Advanced Technology Center for Photonics and Opto-electronic Materials. She worked with electrical engineers, mechanical engineers, and chemists there, she says, and “if they had a laser, I helped them out.” She helped a professor build a CPA laser and assisted a research group that was conducting nonlinear optical characterization of a new pulse amplifying material.
Strickland says she thought she’d be working at Princeton until she retired, but after her husband left Bell Labs in 1996, they returned to Canada. Strickland joined the University of Waterloo’s physics department as an assistant professor. She was promoted to associate professor in 2002. From 2007 to 2013, she served as associate chair of the department.
“When I was young, I just wanted to get a Ph.D. and stay in school,” Strickland says. “Being a professor is the next best thing to being a student.”
She received the IEEE Honorary Membership on 5 May at the IEEE Vision, Innovation, and Challenges Summit and Honors Ceremony, held at the Hilton Atlanta.