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"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," says Johan Mauritsson, an
assistant professor in atomic physics at the Faculty of Engineering,
Lund University.
He is one of seven researchers behind the study, which was directed by
him and Professor Anne L'Huillier.
With the aid of another laser these scientists have moreover succeeded
in guiding the motion of the electron so that they can capture a
collision between 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," explains Johan Mauritsson.
These scientists also hope to find out more about what happens with
the rest of the atom when an inner electron leaves it, for instance
how and when the other electrons fill in the gap that is created.
"What we are doing is pure basic research. If there happen to be
future applications, they will have to be seen as a bonus," adds Johan
Mauritsson.
The length of the film corresponds to a single oscillation of the
light, but the speed has then been ratcheted down considerably so that
we can watch it. The filmed sequence shows the energy distribution of
the electron and is therefore not a film in the usual sense.
Previously scientists have studied the movements of electrons using
indirect methods, such as by metering their spectrum. With these
methods it has only been possible to measure the result of an
electron's movement, whereas now we have the opportunity to monitor
the entire event.
It has been possible to create attosecond pulses for a couple of years
now, but not until now has anyone managed to use them to film electron
movements, since the attosecond pulses themselves are too weak to take
clear pictures.
"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," clarifies Johan Mauritsson.
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