October 24th, 2005
Atoms collide like tennis balls
A team of physicists at JILA, a joint institute of the National Institute of Standards and Technology (NIST) and the University of Colorado at Boulder, has used ultrafast lasers to look at atoms during collisions lasting just half a picosecond (trillionth of a second). And they were able to confirm the theory that atoms — like tennis balls — "briefly lose form and energy when they hit something." These results will help them to better understand other laws of physics at the atomic level.
Below is an image showing how atoms of potassium — like tennis balls — change shape when they collide (Credit: Virginia Lorenz, JILA). Here is a link to a larger version of this image(465 KB).
Here are some short details about the experiments.
Using laser pulses that last just 70 femtoseconds (quadrillionths of a second), physicists have observed in greater detail than ever before what happens when atoms collide.
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).
And how the researchers were able to take ’snapshots’ of the collisions?
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.
This research work has been published by Physical Review Letters on October 14, 2005 under the title "Non-Markovian dynamics in a dense potassium vapor" (Volume 95, Number 16, Article 163601). Here is a link to the abstract.
And for more information about other research projects from this team, you can visit the Cundiff Group web site.
Sources: NIST Tech Beat, October 20, 2005; and various web sites
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