New Laser Maxes Out

Laser blueprint. The souped-up x-ray laser relies on magnetic undulators rather than mirrors.

A team of researchers has pushed an experimental kind of laser to its maximum power output for the first time ever. The mirrorless x-ray laser uses wiggling magnetic fields to channel the power of electron accelerators into a powerful beam of light that is expected to be able to take higher resolution snapshots of molecules and shoot movies of chemical reactions.

In a traditional laser, light waves bounce back and forth between two mirrors at either end of a tube full of a noble gas such as helium or neon. The ricocheting beam forces the atoms to emit additional radiation in phase with the passing light, amplifying the light intensity in the same way a well-timed whack speeds up a whirling tetherball. But this system doesn't work well for short wavelengths of light, such as x-rays. Such light can cut to the heart of the molecular structures of crystals and proteins, but it also slices right through the mirrors in a conventional laser.

Physicists have known for at least 3 decades how to build a mirrorless x-ray laser. They inject bunches of electrons into a several-meter-long tube lined with magnetic "undulators." The undulators wiggle the electrons, causing them to emit x-rays. The rays push back on the electron bunch and break it up into microbunches that radiate in phase with the first burst of x-rays, creating the tether ball-like amplification loop.

Now, a team of physicists led by Efim Gluskin of Argonne National Laboratory in Illinois has pushed its x-ray laser to "saturation," at which the amplification of light intensity hits its theoretical maximum. The saturated laser is about 1000 times more intense than any earlier model, the researchers report in work published online by Science this week. No particular advance triggered the breakthrough, Gluskin says: "This is the result of a decades-long investment in many different technologies."

The new laser holds the promise of huge improvements in measurements of molecular structure, says physicist Jerry Hastings of Brookhaven National Laboratory in Upton, New York, but he cautions that physicists first need some hands-on experience. "Learning how to use this new tool will not be trivial," he says.

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More on x-ray lasers
How conventional lasers work

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