Ultrafast laboratory-based x-ray sources and their applications in chemical research

Abstract

Ultrafast high-intensity laser pulses incident upon condensed matter targets can generate high-density plasmas that emit x-ray pulses with sub-picosecond temporal structure, significant spatial coherence, and high brightness at kilohertz repetition rates. Such laser-driven plasma x-ray sources based on solid and liquid metal targets have been developed in our laboratory. Essential performance features are discussed along with a feasibility evaluation for future routine application in chemical research. Laser-driven x-ray sources are usable for ultrafast x-ray diffraction and ultrafast x-ray absorption spectroscopy. X-ray absorption near-edge spectra of solvated transition metal complexes are presented. Ultrafast molecular dynamics depends on the structure of the solvated molecule before photo-excitation. This solvation structure, in turn, depends on the solute's interaction with the solvent molecules. Furthermore, the solute's vibrational modes and its structure are correlated, solvent dependent, and can be measured by mid-infrared and x-ray absorption spectroscopy. Such measured spectra are presented and correlated with quantum calculations in order to elucidate the solvation environment of various transition metal coordination complexes.