Electron Motion Filmed

An electron's rapid motion has been filmed for the first time, with attosecond laser pulses showing how an electron rides a light wave after being separated from an atom.

Until now it has been impossible to photograph electrons, since their extremely high velocities result in blurry pictures. The movie of electron motion was created by scientists at Lund University in Sweden. Their method involved using a stroboscope and a laser that generates the extremely short light pulses needed to capture the movement of an electron once it is pulled away from an atom.

“It takes about 150 attoseconds for an electron to circle the nucleus of an atom. An attosecond is 10-18 seconds long, or, expressed in another way, an attosecond is related to a second as a second is related to the age of the universe,” said Johan Mauritsson, an assistant atomic physics professor in the Faculty of Engineering at Lund University. He and professor Anne L'Huillier lead the seven-member research team that developed the technology.

While it has been possible to create attosecond pulses for the past several years, it is only recently that researchers have been able to successfully use them to film electron movements, since the attosecond pulses by themselves are too weak to take clear pictures. Scientists have previously relied on indirect methods to study electron movement, such as by metering their spectrum, which only measures the result of the movement. Now researchers can observe the entire event.

In addition to the attosecond laser pulse that helped capture the image, the researchers used a second laser to successfully guide the motion of the electron so they could capture the collision of an electron and an atom on film.

“We have long been promising the research community that we will be able to use attosecond pulses to film electron motion. Now that we have succeeded, we can study how electrons behave when they collide with various objects, for example. The images can function as corroboration of our theories,” Mauritsson said.

They also hope to reveal more about what happens inside an atom when a single electron leaves -- how and when the other electrons fill in the resulting gap.

“What we are doing is pure basic research. If there happen to be future applications, they will have to be seen as a bonus,” Mauritsson said.

The length of the film corresponds to a single oscillation of the light, but the speed was slowed down considerably for the event to be seen by the human eye. The filmed sequence shows the energy distribution of the electron (See the movie here).

“By taking several pictures of exactly the same moment in the process, it’s possible to create stronger, but still sharp, images. A precondition is for the process to be repeated in an identical manner, which is the case regarding the movement of an electron in a ray of light. We started with a so-called stroboscope. A stroboscope enables us to ‘freeze’ a periodic movement, like capturing a hummingbird flapping its wings. You then take several pictures when the wings are in the same position, such as at the top, and the picture will turn out clear, despite the rapid motion,” Mauritsson said.

The research appears in Physical Review Letters.

For more information, visit: www.atto.fysik.lth.se/