The new wave of linear lightsources
I enjoyed your fine article on synchrotron lightsources in the February issue of symmetry. Synchrotron lightsources are indeed useful in a wide variety of applications. However, I would like to point out that not all lightsources are synchrotron-based, which may be inferred from the phrase in the article that begins: “Lightsources are circular particle accelerators ”
Several current and planned lightsources are powered by linear accelerators, such as SLAC National Accelerator Lab's X-ray lightsource, known as the LCLS, and Jefferson Lab's Free-Electron Laser. The Jefferson Lab FEL is primarily an infrared lightsource, but it also produces prodigious amounts of terahertz light and will soon also produce ultraviolet laser light. The LCLS and the Jefferson Lab FEL are each the most powerful lightsources in their class, far outshining older synchrotron lightsources that produce the same wavelengths of laser light. In addition, Jefferson Lab's FEL is built with energyrecovering linear accelerator technology, making its operation highly efficient. The LCLS recently became the world's first X-ray laser at 1.5 Angstrom with brightness far exceeding any source in this wavelength range and is being applied to a variety of groundbreaking scientific measurements. Indeed, the next generation of lightsource user facilities will be based on these developments.
George R. Neil, Thomas Jefferson National Accelerator Facility