Ultrafast time-resolved hard x-ray emission spectroscopy on a table top
Luis Miaja Avila, Galen C. O'Neil, Young Il Joe, Bradley K. Alpert, Niels Damrauer, William B. Doriese, Steven Fatur, Joseph W. Fowler, Gene C. Hilton, Ralph Jimenez, Carl D. Reintsema, Daniel R. Schmidt, Kevin L. Silverman, Daniel S. Swetz, Hideyuki Tatsuno, Joel N. Ullom
Chemical reactions driven by light are fundamental to biology and a source of inspiration for engineering materials to perform tasks such as solar energy harvesting and data storage. Observing and understanding photodynamics requires experimental tools capable of monitoring both atomic and electronic structure on ultrafast timescales. Time-resolved hard x-ray spectroscopies have proven valuable for these measurements due to their elemental specificity and sensitivity to geometric and electronic configuration. However, most of these techniques require intense x-ray beams and can only be performed at large facilities, e.g., synchrotrons and free-electron lasers, where experimental access is limited. Here we present a table-top apparatus capable of performing time-resolved x-ray emission spectroscopy with sub-5 ps time resolution. By combining a compact laser-driven plasma source and a highly efficient array of microcalorimeter x-ray detectors, we were able to observe photoinduced spin changes in an archetypal polypyridyl iron complex, [Fe(2,2-bipyridine)-3]-2+, and accurately measure the lifetime of the quintet spin state. Our results demonstrate that ultrafast hard x-ray emission spectroscopy is no longer confined to large facilities and now can be performed in conventional laboratories with even better time resolution than at synchrotrons. Thus, our apparatus is a novel tool to study spin dynamics in molecular complexes.