Duke Physics Colloquium: Quest for Monochromatic Coherent X-rays
Kwang-Je Kim (Argonne National Lab)
"Quest for Monochromatic Coherent X-rays"
Intense X-ray beams are one of the major tools for studying the structure and interaction of molecules in inorganic material essential for sustain modern civilization and organic material enabling the life. Coherence adds to the power of X-rays as an experimental tool, allowing interference-based techniques. Narrow spectral bandwidth together with tunability further enhances the capabilities by providing methods to identify elements and their environment. A packet of X-ray beam is coherent if it occupies a minimum phase space volume as given by wave mechanics. Having gone through several generations of advances, research facilities based on storage rings are currently at the 4th generation stage. Undulators from 4GSR (4th generation storage ring) facility produces transversely coherent X-ray beams of ~1% bandwidth. Recently, X-ray free electron lasers (XFEL) became feasible in which the spontaneous emission is self-amplified in a long undulator by a factor about a million, giving rise to intense, quasi-coherent X-ray pulse. An XFEL is capable to produce ultrashort X-ray pulses, permitting the study of femto-attosecond dynamics. XFELs driven by super-conducting RF (SCRF) linacs produce a constant stream of X-ray pulses with MHz repetition rate than that from Cu-linacs, and proportionally higher X-ray brightness. X-ray FEL oscillators (XFELOs) are also being developed... Please see website for full description.