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Exploring how light, matter interact

jbrehm2, February 18, 2015 | View original publication

Exploring how light, matter interact

Observing what happens in one-trillionth of a second – the opening moves in photosynthesis, for example – requires precision and extremely fast devices. UNL physicists are expanding their experimental and theoretical arsenals to help unlock the mystery of how light interacts with matter.

Their discoveries will broaden understanding of how light interacts with atoms, molecules and nanostructures. These findings could one day lead to devices that convert light energy more efficiently, such as improved solar technology and computers that perform calculations far faster than currently possible.

Over the next two years, UNL is building new devices from scratch that will enhance its capabilities for observing ultrafast processes.

“This will really build up the infrastructure at UNL to produce new science,” said Anthony Starace, George Holmes University Professor of Physics. “Ultrafast science is the next step in humanity’s ability to understand nature and ultimately control these processes.”

More than a dozen UNL physicists and engineers are collaborating with colleagues at Kansas State University and the University of Kansas on the Nebraska-Kansas Consortium, a partnership to expand all three universities’ capacity to study atomic, molecular and optical physics. The tools they develop could have applications in laser technology, solar energy capture, nanotechnology and optoelectronics, the combination of electronics with light.

Funded by the National Science Foundation’s Experimental Program to Stimulate Competitive Research, or EPSCoR, the consortium grew out of periodic “Wild Corn” conferences at which UNL and KSU physicists shared ideas and information. The conference name draws from the schools’ mascots: Cornhuskers and Wildcats.

“We always said it would be great if we could collaborate,” Starace said. “But there was never such an opportunity as this until now.”

The consortium is taking two approaches to observe and control ultrafast processes. The first approach is based on the premise of stop action made famous by 1925 UNL alumnus Harold Edgerton and his iconic image of a bullet piercing an apple.

Today, scientists use electron and laser pulses operating faster than the process being observed to capture the action in images recreated from electron scattering. This approach is helping physicists understand, and ultimately control, the molecular changes that occur when light strikes molecules, during photosynthesis or human vision, for example.

Some processes happen too fast to capture with current technology. To overcome these limitations, UNL physicists Martin Centurion and Matthias Fuchs are designing and building a new source of electron pulses that uses high-powered lasers to accelerate electrons even faster.

They hope the new equipment will create images from a single pulse rather than requiring numerous repetitions. A single-shot experiment would help elucidate ultrafast transformations in solids whose structures, like those of Edgerton’s apples, are destroyed by the process. This breakthrough would open new avenues in materials science research.

When completed in about two years, this new equipment will be the first to have achieved this level of detail, Centurion said.

The second approach uses light pulses to overcome the relatively slow speed of electronics, which is based on the movement of electrons. Light photons travel significantly faster than electrons, so merging light with electrons near specially created nanostructures may result in much faster computers and other electronic devices.

The EPSCoR grant enables collaboration between researchers who can make nanostructures and those who are experts at controlling short pulses of laser light and electrons.

The consortium includes 30 physicists, chemists, computer scientists and electrical engineers at UNL, KSU and KU. Thirteen UNL researchers are participating. Starace, Centurion and physicist Herman Batelaan lead UNL’s consortium participation. Overall project leaders are Fred Choobineh, UNL electrical engineering professor and director of Nebraska EPSCoR, and Kristin Bowman-James, KU chemistry professor and director of Kansas EPSCoR.

The consortium also will provide educational and outreach activities to broaden participation in UNL and KSU research among high school students as well as students and faculty from small Nebraska and Kansas colleges, especially students underrepresented in science and engineering. Other activities include expanding student participation in UNL’s annual Undergraduate Women in Physical Sciences conference and hosting high school teachers at summer workshops and events.

Starace said the workshops’ goals are to improve learning of high school physics by focusing on ways to overcome student misconceptions. In addition, teachers will learn about the latest research and how to incorporate it into their teaching. This, in turn, will attract more students to careers in physics or engineering.

NSF EPSCoR is supporting the consortium with a three-year, nearly $6 million award, of which UNL received nearly $2.5 million, with $500,000 retained by Nebraska EPSCoR for support of the project’s research and outreach activities. Kansas EPSCoR and participating Kansas universities received the other $3 million. The Nebraska-Kansas Consortium is one of three science and engineering consortia funded by the program nationwide.