Spring Issue — June 2008
Freeze Frame Physics
Cutting-edge laser technology is allowing University of Ottawa researchers to manipulate electrons at almost unimaginable speeds — measured in attoseconds — and see chemical reactions as they unfold.Manipulating electrons in attosecond time could potentially allow scientists to control and change chemical reactions in new ways, leading to advances in everything from medicine to engineering.
Just how fast are these electrons moving? To put it in context, comparing one attosecond to one second is like comparing one second to the age of the universe — which is almost 14-billion-years old.
“This is the real time scale of matter. Attosecond science lets us look at the microworld of atoms and molecules on its own terms,” says Paul Corkum, a physicist with the National Research Council Canada (NRC), who was recently awarded a Canada Research Chair in Physics at the University of Ottawa.
Corkum and his team use lasers to fire intense light waves at a gas made up of molecules. The light tugs electrons out of their orbits, making the atoms in a molecule fly off in one direction and the ions in another.
A molecule is composed of many electrons moving around a set of ions. The electrons stay in place because of the attraction between their negative charge and the positive charge of their ions.
The electrons help make the ions stick together, forming a molecule. Focusing a laser directly on a molecule pushes both the positive ions and the negative electrons, trying to move them in opposite directions. Since the electrons are not as massive as the ions, they give in first.
Researchers use computer graphics to visually represent how a molecule looked before its electrons were manipulated. In the laboratory, one approach to “seeing” a molecule is to “blow it up.” A very intense laser pulse removes many of the molecule’s electrons all at once. With the electrons gone, the molecule’s ions explode.
As Corkum then explains, by catching the ions you can put the pieces back together to see what the molecule looked like.
“If you do this many times, each explosion becomes like a frame in the movie of a chemical reaction,” he says.
Of course, researchers want to do more than just watch electrons move around — the real prize will be in applying attosecond science.
For example, by controlling how atoms, in attosecond time, release x-rays, an x-ray laser could be developed that could lead to new kinds of x-ray machines. By using an intense laser pulse, it is possible to create a portable x-ray machine that could be used outside a hospital.
The same approach could lead to building bright ultrafast x-ray machines for inside hospitals. Bloodless, non-invasive surgery is another potential new field made possible by short, intense laser pulses.
Computer scientists are also excited about attosecond science. There are possible applications for magnetic information-storage devices, which would lead to much more powerful computers.
“This field has exploded. It is a big international effort,” says Corkum. His lab reflects the international diversity of attosecond science. Indeed, researchers and postgraduate students from Europe, Israel, Japan and the United States have come to Ottawa.
The lab’s status is also keeping homegrown talent at the University of Ottawa. Julien Bertrand, a second-year physics Ph.D. candidate considered London’s Imperial College and other leading centres before deciding to stay in Ottawa.
“I have access to very hi-tech equipment and the ability to do experiments at a higher level than I would in most other facilities,” says Bertrand. “I’m also free to present data to the NRC scientific community. I don’t have to wait until I go to a conference.”
Exactly how attosecond research will push the boundaries of science is impossible to say. But the future looks bright.
“We know that every other advance that’s led to shorter laser pulses has led to major scientific gains,” Corkum says. “This is the next step.”
“Attosecond science lets us look at the microworld of atoms and molecules on its own terms.”