In The Field

APS March: Zeptoawesome

I took a random walk through the convention centre this morning and stumbled into a talk by Margaret Murnane, a researcher at JILA and one half of laser-jocky-power-couple Murnane-Kapteyn.

For years now, Murnane and her husband have been building some of the fastest lasers in the West (well actually some of the fastest lasers anywhere). When I first started as a journalist they were femtosecond (10-15 sec), then they were attosecond (10-18 sec). And in today’s talk, Murnane told the audience that she believed the prefix zepto (10-crazy short) was within reach.

Murnane’s set up is really cool and deserves a few words. Basically the scheme is to zap a little vile of noble gas with a very bright infrared laser. The laser field is so powerful that it can kick an electron out of an atom… Well sort of. Actually the laser kicks out half the electron’s wave function (in other words, the electron is sort of simultaneously in and out of the atom). The half on the outside interacts with the the light and is spread out before recombining with the half on the inside. When the two combine it creates a powerful interference pattern that radiates a broad spectrum pulse of x-ray light.

That’s the really complicated version. The easy version (which Murnane was kind enough to explain to me after the talk) is to think of the gas like a guitar. The laser light “plucks” the electrons really hard, creating a lot of powerful harmonics.

While the spectrum of the light is broad, the length of the pulse in time is really narrow. So narrow in fact that Murnane believes it may soon be possible to make zeptosecond pulses (that’s 10-21). Pulses that short give us “the ability to capture all motion in our natural world,” she told the crowd. In other words, it may be possible to make movies of even the shortest events, like electron excitation. Zeptoawesome.


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