Collaborating couple pursues next generation of lasers
When the first functioning laser was unveiled in 1960, people had no idea it would be used for surgery, let alone in bar-code readers and CD players. Experts speculated that the new device might be used to peel potatoes or to erase typing errors.
Henry Kapteyn, a professor of physics at the University of Colorado, chuckles about that last example. “Wite-Out works a lot better,” he observes. And impact of the laser on information technology, which made the internet possible through fiber-optic communications, has clearly proved to be far greater than these early researchers envisioned.
Margaret Murnane, a distinguished professor of physics, is Kapteyn’s collaborator. The pair, which is joined in research and in matrimony, is expanding the frontiers of laser technology.
Murnane and Kapteyn are developing high-energy, short-wavelength X-ray lasers that have a host of promising medical and technological applications. But they admit they are not sure how their work will ultimately be employed.
“Probably in 20 years people will laugh at some of the things we do,” Kapteyn says. Somehow, that seems unlikely.
The work of Murnane and Kapteyn is routinely published in top academic journals—in November, for instance, Science published two of their articles, and one was the cover story. They won the 2009 Ahmed Zewail Award in Ultrafast Science and Technology, an award deemed “prestigious” by the National Research Council. A litany of other honors trails their names.
The lasers Murnane and Kapteyn work with create X-ray laser pulses that last about 10 femtoseconds. A femtosecond is one-quadrillionth of a second; a second, by comparison, is about one-quadrillionth of 32 million years. “Superfast” says it well.
Murnane and Kapteyn are pioneers in this field, being the first to build a sub-10-fs laser.
“Electrons are what we want to look at,” Murnane says. Molecules are held together with clouds of electrons, which move very fast. What scientists don’t yet understand is what is happening when a molecule breaks apart, an event that occurs with great rapidity.
“How do the electrons and atoms talk to each other? This is a fundamental question in chemistry,” Murnane says. Answering it may have significant implications for photovoltaics and energy conversion, she adds.
Kapteyn mentions one of their recent articles in Science, which reported that an X-ray laser was used to “pluck” an electron from a molecule. In the process, they created excited molecular states that cause the molecule to rapidly fall apart.
Another one of their recent experiments seeks to understand heat dissipation in nanoelectronics. Electronic circuits have gotten very small, but as wires and junctions have gotten smaller, it’s become more difficult to cool these circuits effectively, Murnane says.
In a microcircuit, a little bit of heat must be dissipated every time there’s a switch. The question is how fast can it dissipate, Kapteyn says. To look at heat flow in a nanostructure, you have to model and measure it. If the heat dissipates quickly, transistors can be made smaller.
Murnane notes that superfast lasers could help in the biological sciences as well. She and Kapteyn hope to develop superfast, X-ray lasers that could help scientists observe biomolecular processes in three dimensions. She says that’s an “ultimate goal,” though “not very close” to being realized.
Murnane notes that the structure of many proteins is not well understood, particularly with respect to what part of a biomolecule is most important. In some cases, the molecular structure is not known; in others the reaction site is unknown. Being able to perceive those structures and processes would be, she says, “the holy grail.”
“We’re not close to being able to doing it. But that would be great.”
One application of such an advance would be in pharmaceuticals. “If you can’t see the reaction happening, it’s harder to know how to optimize it,” she says.
Kapteyn emphasizes that one over-arching goal is to make coherent x-rays, which can capture images at very high resolutions, hundreds of times higher than with current microscopes. Two very large facilities are being developed to do such work, but they are very expensive, and only one researcher may use a facility at a time. The usefulness is therefore constrained.
One of the duo’s goals is to develop a desktop-sized machine that could perform biomolecular tomography, he adds. “To get there, there’s a lot of interesting physics we have to do.”
Murnane gently demurs, noting, again, that it’s hard to speculate which application of their work might become widely accepted and used. Kapteyn nods. They move on.
Kapteyn and Murnane have been having such collegial debates for years. They met in graduate school at the University of California at Berkeley. Early on, they decided that collaborating together would help them compete with larger and better-funded research groups.
The strategy seems to work. As a team, Murnane and Kapteyn have learned the value of compromise and discussion. “You have to buy into the fact that you’re not always right, and you actually gain by listening,” she says.
They say marriage and scientific collaboration are complementary. “I would never want to do science alone,” Murnane says. “It’s too boring.”
People ask if they just talk about work at home. They don’t, he says, adding that they never have to ask, “Honey, how was your day at work?” But if one partner has a great idea at 10 p.m., they can discuss it.
Murnane and Kapteyn are fellows in CU’s Joint Institute for Laboratory Astrophysics. Kapteyn won the National Science Foundation Young Investigator award in 1992 and the Optical Society of America’s Adolph Lomb Medal in 1993. He was elected a fellow of the American Association for the Advancement of Science in 2008.
Murnane is a fellow of the American Physical Society and the Optical Society of America. In 1997, she won the Maria Goeppert-Mayer Award of the American Physical Society. In 2000, she was named a John D. and Catherine T. MacArthur Fellow, often called a “genius grant.” In 2004 she was elected to the National Academy of Sciences, and in 2006 she was elected a fellow of the American Academy of Arts and Sciences.
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