New x-ray source is magnitudes brighter than high-gain FELs

Researchers at Argonne National Laboratory (Argonne, IL) and the University of California at Los Angeles (UCLA) are developing an x-ray free-electron laser (FEL) in an oscillator configuration—called X-FELO—that has the potential to provide a coherent source of x-rays several orders of magnitude higher in average spectral brightness than those produced from a high-gain FEL in a standard self-amplified spontaneous-emission (SASE) configuration.

By using crystals to create a low-loss x-ray cavity, an x-ray pulse can be repeatedly amplified by traveling together with electron bunches from an accelerator. The pulse evolves from an initially incoherent spontaneous emission into a coherent pulse as its intensity rises exponentially. Compared to SASE from a high-gain FEL, pulse intensity of an X-FELO is two or three orders of magnitude lower; however, the X-FELO spectrum is narrower by more than three orders of magnitude and the pulse-repetition rate (approximately 1 MHz) is two orders of magnitude higher. X-rays from 5 to 20 keV in energy made possible by the X-FELO could improve nuclear-resonance and inelastic-scattering measurements, and improve hard x-ray photoemission spectroscopy. Contact Kwang-Je Kim at [email protected].