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K-State Today

May 25, 2011



Small start, big results: Physicist's atomic pursuit credited to program's progression, international acclaim

By Julie Fosberg

For 40 years C. Lewis "Lew" Cocke has been blowing apart atoms inside the James R. Macdonald Laboratory at Kansas State University.

Cocke, who this week trades his title of K-State university distinguished professor in physics for that of professor emeritus, has been researching destruction on a molecular level in an effort to better understand matter. This pursuit has helped propel K-State's atomic, molecular and optical physics program to an internationally recognized level.

U.S. News and World Report ranks K-State's atomic, molecular and optical physics program -- of which Macdonald Laboratory is the main component -- as 13th in the country. Decades of work, discoveries and recognition by and for Cocke and his K-State colleagues made it possible for K-State to host the biennial International Conference on Attosecond Physics in 2009, which brought around 200 physicists worldwide to Manhattan.

But reaching these achievements wasn't always a straightforward trajectory, said Cocke, who is associate director of the lab.

Macdonald Laboratory, located in the subbasement of Cardwell Hall, was built in 1967 and originally named the Nuclear Science Laboratory. It wasn't until the 1980s that the facility was named in honor of its K-State founder. In 1969 a Tandem Van de Graaff particle accelerator was added to the lab. The accelerator was built for nuclear physics, though by the time it was installed at K-State it was obsolete for that field, Cocke said. It had, however, been overlooked as a tool for studying ion-atom collisions, a field that was relatively unexplored. In repurposing the accelerator, the Macdonald Laboratory became one of the first facilities to study atomic physics.

"I will modestly say that we were among the world's leaders in this area. It was a big area for about 25-30 years, and a big area for us for 30 years," Cocke said. "Jim Macdonald, Pat Richard and I, along with a number of other people throughout the years, got in at the bottom and that put us on the map for this field."

In the mid-1980s the department received a $5 million capital equipment grant from the U.S. Department of Energy, allowing for the Tandem accelerator to be upgraded with a linear accelerator, or LINAC, which produced higher velocities for collisions. Also added was a Cryogenic Electron Beam Ion Source, or CRYEBIS, that produced highly charged ions that move at slow speeds. This generated matter could reach temperatures nearly 60 million degrees Celsius, and ushered in a new focus on heavy charged ion work.

"That work was kind of an extension of ion-atom collision, but a very specialized part," Cocke said. "A highly charged ion is just an atom from which many electrons have been stripped. It's what you would encounter in a very high temperature plasma and gas in nuclear physics reactions and at the center of the sun."

Macdonald Laboratory was only one of a dozen facilities in the world that could explore this field.

In the late 1990s Cocke and the others believed heavy charged ion work had mostly run its course, so the lab switched to intense laser work, the research focus it continues to this day. With the addition of Zenghu Chang, a physics adjunct professor, they built an ultrafast high intensity laser source called the Kansas Light Source in 2001. The light source fires very short laser pulses into atoms at nearly a billionth of a billionth of a second.

"It sends out about a thousand pulses a second. If we could slow down the speed of light, those pulses would look like little pancakes that are about a thousandth of a centimeter wide," Cocke said. "We make two of these at about a thousandth of a millimeter apart, and ping them against the atom. This makes the molecule start vibrating because it lost an electron. Then the next pulse hits it. How it gets blown apart depends upon how much it moved in between."

In doing this, researchers are able to control the reaction that occurs within a molecule rather than just observing what happens from running an ion by an atom.

"It's sort of like watching a movie at an atomic scale," Cocke said. "And this is the basic idea behind the whole field: the ability to take real-time pictures of the motion of electrons, atoms, heavy nuclei and molecules on a real-time basis."

Knowledge from this field might one day enable researchers to tailor molecules that improve health care, energy and homeland security.

Although Cocke is stepping away from the lab and program his peers credit him with largely helping to guide and flourish, he won't be far from the field as he plans to continue his work.

"As a physicist I can't just turn my brain off," Cocke said. "I've spent all my life working with atoms and molecules, even though I've never seen one. But mentally, I know they're there."