Laser researcher reaches the pinnacle of his profession

	Paul Corkum Ph.D. '72

In a show-stopping session at the Conference for Lasers and Electro-Optics (CLEO) in Baltimore last month, Paul Corkum Ph.D.’72, received two prestigious awards for his research, the Institute of Electrical and Electronics Engineers (IEEE) Quantum Electronics Award and the Optical Society of America (OSA) Charles H. Townes Award, named after a pioneer in the development of lasers.
Only four awards are given at CLEO each year, and until Corkum, no one had won two during the same year. And Corkum’s amazing week didn’t end there.
When Corkum returned to his home in Ontario, Canada, he learned that he had been accepted as a member of the Royal Society of Britain, joining the ranks of prominent scientists such as Isaac Newton and Charles Darwin.
“I’ve reached the peak in my career,” Corkum jokes to his co-workers at Canada’s National Research Council (NRC) where he works as Project Leader. “A week like that won’t happen again.”
Building on other people’s work
Although he’s pleased, Corkum isn’t bragging. Instead, he views the awards as recognition of the importance of his field. “The awards are not only for me, but for my whole sub-field,” he says. “Scientists always build on other people’s work.”
Corkum is studying quantum electronics, which, he says, “is just a complicated way of saying ‘lasers.’” He and his fellow researchers are using lasers to see unimaginably fast chemical reactions and movements of molecular particles.
Humans live in seconds, Corkum explains. Cameras can capture action without blurring with a flash 1 /1,000 of a second. Televisions smoothly blend motion in frames changing every 10/1,000 of a second.
In chemistry, interactions between atoms occur much faster. These interactions take place in a femtosecond – that’s one over 10 with 15 zeros (1/1,000,000,000,000,000) of a second. “The ratio of a femtosecond to a second is the same as the ratio of a second to the age of the universe,” Corkum explains.
Electrons, tiny orbiting parts of an atom that hold molecules together, need an even smaller increment of measurement to see their movement. This measurement, called the attosecond, is one over 10 followed by 18 zeros (1/1,000,000,000,000,000,000) of a second.
Corkum has found a way to photograph electrons moving at speeds measured in attoseconds. He uses lasers, which emit light beams, to exert force on a charged atom. Light travels in waves like water. When the waves hit the electron attached to atom, the electron moves.
Corkum compares the forces on the electron to a person pushing a swing. “The light jiggles the electron the same way we would jiggle a swing,” Corkum says. When the force from the light on the electron becomes too strong, the electron will break free from the atom like a swing flying out away from its base. But the electron can only fly out so far before the force of the wave drives the electron crashing back into the positive atom. So both the electron and the swing return to the spots they occupied before.
Doing what’s never been done
When the electron returns to the atom, it gives off energy in the form of light. The scientist can control the amount of force applied to the electron, and, thereby, control the length of time light is given off even down to the attosecond.
Corkum’s newest research involves photographing electrons in motion. Corkum and his team took a picture of an electron on a nitrogen molecule. “It was the first time anyone had really taken a snapshot of an electron,” Corkum says.
To take the picture, he shoots light waves at the molecule. One electron breaks free and then crashes back. The electron snaps the picture, like the flash of an ordinary camera. After collecting many pictures, Corkum hopes to combine them into a movie that would allow researchers to watch electrons orbit atoms.
The realization that lasers could be used to visualize electrons came slowly to researchers. As lasers improved, Corkum and other scientists throughout the world became intrigued. They thought, “Wouldn’t it be interesting to shine lasers on molecules and atoms.” It had never been done, so Corkum and others tried it. “Piece by piece,” Corkum says, “we began to think [the process] through and understand how it works.”
Then one day, all the pieces came together for Corkum. “It hit me like a block. Bang!” Corkum says. In that moment of clarity he realized that the electron worked “just like a swing.” If the electron moved like a swing, Corkum realized he could control that motion.
Corkum first became involved in lasers when he was hired by Canada’s NRC after earning his Ph.D. at Lehigh. During that time, jobs in physics were hard to find. Although Corkum received his Ph.D. in theoretical physics, he applied for a post doctorate position that involved laboratory work at the NRC. Most of the time, physicists specialize in theory, which focus on formulas, or in laboratory work. Little overlap occurs between the two areas of specialty, so the NRC recruiters hesitated when hiring Corkum.
“The people at the NRC wanted to know if I could do lab work,” Corkum says. While at Lehigh, Corkum had taken apart his entire car engine and rebuilt it again. “When I told them that I rebuilt my car, they gave me the job,” he says. While at NRC, he learned more about lasers and matured as a scientist “step by step.”
Corkum found his degree in theory helpful in this process. “Getting my Ph.D. in theory and then moving to experiments gave me an advantage,” Corkum says. “It allowed me to look at the problem from both sides and broaden my approach.”
Inspired by ‘the smartest guy’
Corkum remembers his graduate work at Lehigh fondly. “I had a great time at Lehigh,” he says. After attending Acadia University for his Bachelor’s degree, Corkum left Canada for Lehigh. Since he had grown up in a smaller region in Nova Scotia, Corkum chose Lehigh for its comfortable size and cutting-edge technology. Even so, when he arrived, Corkum was amazed at his new “big, fancy school.”
As a graduate student, Corkum was inspired by his professor, James McLennan. “McLennan understood everything,” Corkum says. “I can remember thinking he was the smartest guy. I could never be as smart as he.”
Although in his opinion Corkum may not have surpassed his mentor, he has received much applause from the scientific community. Corkum has received many prestigious awards for his work in quantum physics, including the Canada’s highest physics award, the Canadian Association of Physicists gold medal for lifetime achievement in physics. He is also a Fellow of the Royal Society of Canada. Corkum has been given the Einstein Award given by the Society for Optical and Quantum Electronics, her Majesty Queen Elizabeth II’s Golden Jubilee Medal and the Tory Medal of the Royal Society of Canada.
Corkum plans to continue exploring quantum electronics at the NRC of Canada.
--Becky Straw