Where the LCLS Ends: The AMO Instrument
When the Linac Coherent Light Source starts producing the world's first hard X-ray laser pulses later this year, they will all be headed to one place: the Atomic, Molecular and Optical science instrument. A complex creature comprising spectrometers, focusing optics, and a synchronized high-power optical laser, the AMO will be the first instrument in operation at LCLS—and the only one until March 2010.
"We designed the AMO instrument to take advantage of the two unique features of the LCLS: unprecedented energies and unprecedented temporal resolution," said AMO Instrument Scientist John Bozek, who joined the LCLS team three years ago after more than a decade at Berkeley Lab's Advanced Light Source.
In its first experiments, the instrument will shine LCLS's unique light on relatively simple forms of matter—atoms and molecules. In these minimalist systems, researchers can follow where all of the beam's energy ends up, something too complex to do with solids where energy can leak out into the material's bulk. These experiments will offer an in-depth understanding of how the LCLS beam interacts with matter.
In a slightly flashier application, the AMO instrument will also make stop-action movies of molecules in action. The short, quick, repetitive bursts of LCLS X-rays enable the AMO instrument to take individual photos as molecules move and interact. By stringing together many such images, researchers will create movies that reveal the fundamental behavior of molecules on unprecedented timescales.
The instrument, Bozek said, has been "very well received" by its future users. Last year, the LCLS received 28 proposals—involving over 200 scientists from 16 countries—for AMO beam time. A panel ranked 12 of these proposals as pressingly important, and those experimenters will begin arriving at SLAC this September. The first round of data-taking will run through December 2009.
One of the AMO experiments will study how lasers can be used to control molecules. A high-power laser will first orient a sample of molecules within the AMO instrument. A fraction of a second later, researchers will unleash the LCLS beam to ionize the molecules, stripping away their electrons. By stringing together a series of photographs timed at various points after the LCLS blast, researchers will be able to make movies of molecules responding to the laser excitation. This helps to provide an understanding of the electronic structure of matter—the ground state and excitations of the electrons, which determines many of matter's properties—as well as the interaction of the laser with the sample.
"People are beginning to use lasers to control molecules, but only with the LCLS can we start to probe this, using the tools that have been developed at synchrotron light sources over the past few decades," Bozek said.
Before any experiments get underway, however, Bozek and his team will need to finish assembling the instrument. "Right now," he said, "we're still buying all the parts." Once the equipment arrives, it will be assembled in Mechanical Fabrication Department shops, then installed in the LCLS Near Experimental Hall in June.
"I can't wait to get it here and tinker with it," said Bozek. "There's a lot of excitement here [at SLAC] and within the user community about this start-up. It's going to be fun."
For more images and an animation showing the instrument, see the LCLS AMO Web page.