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JILA scientists used
brief flashes of laser light to reveal how atoms, like tennis
balls, briefly lose form and energy when they collide.
Image credit: V. Lorenz,
JILA
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The new data, reported in the Oct. 14 issue of
Physical Review Letters,* provide the equivalent of missing frames in
movies of colliding atoms (see simulated images in accompanying
graphic). As is the case when a tennis ball is hit by a racquet, the
motion is too quick for the eye but can be detected using short
flashes of light. The JILA scientists collected data on atoms'
properties before, during and after collisions lasting just half a
picosecond (trillionth of a second) using laser "flashes" that were
even faster.
In the JILA experiments, about 10 quintillion
potassium atoms in a dense gas were packed into a titanium container
just 1 square centimeter in size and heated to 700 degrees C (almost
1,300 degrees F). With such high temperatures and large numbers of
atoms, the experiment is designed to maximize the number of atom
collisions. Rapidly alternating pulses of laser light then are used to
"freeze frame" the action.
Energy from the first laser pulse is absorbed by
the atoms, placing them in a uniform state, emitting electromagnetic
waves in identical patterns. A second laser then quickly hits the mass
of atoms, and a detector captures a signal beam formed by the
interaction of the beams. Light from the second pulse is absorbed and
re-emitted by atoms that are "in synch" but not by atoms that are
colliding and losing energy. The intensity of this signal beam,
measured as a function of the delay between the two pulses, provides a
"snapshot" of how many atoms are colliding at any one time, as well as
details about changes in their wave patterns. |
