Lighting the way

2 persons standing in front of a wall which is written "Lightning the way" on it

“If we can see the actual structure of complex molecules and make movies of chemical reactions, we can, for example, design better drugs and treatments.”

– Thomas Brabec

In a memorable quote, American theoretical physicist Richard Feynman once declared that “Physics is like sex: sure, it may give some practical results, but that’s not why we do it.”

University of Ottawa physics professors Thomas Brabec and Lora Ramunno would likely concur. When they speak about their research, it quickly becomes apparent that they are driven by an innate fascination for the fundamentals of their science.

Brabec, a Canada Research Chair in Ultrafast Photonics who was recruited from the Vienna University of Technology in Austria, talks about the “experimental thrill” of the work he does. Among other things, he is developing theoretical techniques to take freeze-action images of electrons “buzzing around,” building on an idea that was originally conceived by Paul Corkum, a world-renowned University of Ottawa physics professor and National Research Council scientist (see page 10) with whom Brabec did post-doctoral work in the mid-1990s.

“Molecular reactions are the basis of our world,” he explains, “And making a movie of molecular bonding is a really exhilarating prospect.”

Electrons move at an attosecond scale, which is 10-18 or a billionth of a billionth of a second. Working with ultrafast pulses of light, Brabec takes “snapshots” of these electrons, both in terms of where they are in space and in time.

“It’s like a stroboscope,” he adds. “Like those famous 19th-century images of the galloping horse caught in stop-action photography.”

These ultrafast imaging techniques have been proven with small molecules, Brabec explains, “but bringing them to large systems, such as bigger molecules or complex reactions, is a whole other story.”

Imaging such complex molecular systems is extremely challenging. So is the theoretical modelling of the imaging process, which is complicated because it involves many electrons. Brabec and his team are modelling the dynamics of up to eight electrons in intense laser fields, and they are looking at modelling the imaging of small molecules such as methane, which has not been possible so far. “We’re at the limit of what our computers can do at the moment.”

He is also working with the x-ray free electron laser (XFEL), which creates X-rays at such high intensities they quickly blow matter apart. “There is so much interest in the XFEL because it has the potential to take an image of a single large biomolecule without having to crystallize it,” says Brabec. “The question we are trying to answer is whether the snapshot can be taken before the molecule is blown up. Right now, images are taken by synchrotrons using low light intensity and to see anything the molecule has to be crystallized. We never know if it’s the true molecule we’re seeing. The exciting part of our work is that XFELs may be able to take snapshots of molecules in their most natural state.”

As Canada Research Chair in Computational Nanophotonics, Ramunno also conducts studies at an exceedingly small scale and at a foundational level. “I just really like to figure out how things work,” she explains. “I want to understand the fundamental processes.”

She looks at the interaction of laser light with materials on length scales that range from a micrometre (one thousandth of a millimetre) to a nanometre, which is 1,000 times smaller. “Lasers have become commonplace in today’s world,” says Ramunno. “But when you look at the way lasers interact with matter over such a small space, you can see new physical phenomena that are well beyond our everyday experience.”

As a theoretical physicist, Ramunno uses computational simulations to understand how focused bursts of intense light can blast tiny, intricate structures in materials. Like Brabec, she also develops computer models of better ways to take pictures of molecules, but she is focused on creating 3D images of distributions of molecules within a large sample. She is particularly interested in how nanoscopic substructure can distort images.

While Ramunno and Brabec work at a purely theoretical level, they fully recognize the potential applications of their research. For example, Ramunno’s simulations of intense lasers and glass may help in designing better microlenses, biosensors or data transport materials, while her study of molecule-specific imaging can be used to create better microscopes for imaging subcellular biological processes in real time.

“I like to work in areas that have applications, even if I’m not the one implementing them in a lab,” she says.

Brabec’s research could also lead to practical discoveries. “If we can see the actual structure of complex molecules and make movies of chemical reactions, we can, for example, design better drugs and treatments,” he says. “Right now, we base a lot of our knowledge on very powerful theories, but are they really correct? Nobody knows. Seeing is believing, and seeing is understanding.”

Both Ramunno and Brabec share the desire to work more closely with their experimental physics colleagues, and agree that the new Advanced Research Complex will be instrumental in facilitating more of those kinds of interactions.

“Right now we’re spread out all over campus,” explains Ramunno. “If our experimental colleagues are right next door, that will really help us develop our ideas. That’s what we need as theorists.”

 

by Leah Geller

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