Researchers take important step toward developing cavity-based X-ray laser technology
Researchers have announced an important step in the development of a next-gen technology for making X-ray free-electron laser pulses brighter and more stable. They used precisely aligned mirrors made of high-quality synthetic ...
Setups like these are at the heart of cavity-based X-ray free-electron lasers, or CBXFELs, which scientists are designing to make X-ray laser pulses brighter and cleaner—more like regular laser beams are today.
"The successful delivery of a cavity-based X-ray free-electron laser will mark the start of a new generation of X-ray science by providing a huge leap in beam performance," said Mike Dunne, director of the Linac Coherent Light Source (LCLS) X-ray laser at the Department of Energy's SLAC National Accelerator Laboratory, where the work was carried out.
"There are still many challenges to overcome before we get there," he said. "But demonstration of this first integrated step is very encouraging, showing that we have the approach and tools needed to sustain high cavity performance."
The SLAC research team described their work in a paper published in Nature Photonics. Early results were so encouraging, they said, that the lab is already working with DOE's Argonne National Laboratory, its longtime collaborator on the subject, to design and install the next, bigger version of the experimental cavity system in the LCLS undulator tunnel.
Making X-ray laser pulses more laser-like
Despite their name, X-ray laser pulses are not yet fully laser-like. They're created by making accelerated electrons wiggle through sets of magnets called undulators. This forces them to give off X-rays, which are shaped into powerful pulses for probing matter at the atomic scale. At LCLS, pulses arrive 120 times a second, a rate that will soon increase to a million times per second.
A top-down view of one of the cavity vacuum chambers. Two diamond mirrors can be seen in the upper and lower left corners, each one mounted on four motors that control its angle and position. At upper right, the precision diamond grating that brings X-ray pulses into the chamber is mounted on a screen holder. Credit: Diling Zhu/SLAC National Accelerator Laboratory
SLAC and Stanford PhD student Rachel Margraf and SLAC scientist Gabriel Marcus align the cavity's four diamond crystal mirrors from the experiment's control room. The mirrors appear in the two upper left monitors; monitors at desk level are used to control motors that make small angular adjustments to the mirrors. Credit: Diling Zhu/SLAC National Accelerator Laboratory
The experimental apparatus is shaped roughly like a barbell, with two boxy vacuum chambers at the ends and beam pipes connecting them. X-ray pulses travel from the front cavity chamber to the back one through one pipe, then back to the front cavity through the other pipe, completing a 46-foot loop. Diamond mirrors inside the cavities guide the pulses along precisely the right path. Credit: Diling Zhu/SLAC National Accelerator Laboratory
Precision diamond gratings (orange and green squares) are used to bring X-rays in and out of the X-ray cavity. Room light bouncing off their intricately etched nanostructure produces the colors we see, much as water droplets in the atmosphere refract light into rainbows. The colors of the gratings change when viewed from different angles. Credit: Diling Zhu/SLAC National Accelerator Laboratory