http://www.sciencemag.org/news/2021/08/tiny-diamond-mirrors-could-smooth-out-already-revolutionary-x-ray-lasers

Magnets called undulators stretch roughly 100 meters down a tunnel at SLAC National Accelerator Laboratory, with one side (right) producing hard x-rays and the other soft x-rays.

Twelve years ago, physicists turned on the first x-ray laser, and since then it and several others around the world have proved themselves revolutionary probes of materials and molecules. But the devices, called x-ray free-electron lasers (XFELs), are only partially laserlike. In contrast to the pure, single-wavelength light emitted by conventional lasers, they produce noisy, chaotic beams. Now, physicists are developing a scheme that would enlist perfect diamond mirrors to make the x-ray pulses much more like ordinary laser beams and even more useful.