Femtosecond x-ray fluorescence

Using few-cycle-driven coherent laser harmonics, K-shell vacancies have bee n created in light elements, such as boron (E-B = 188 eV) and carbon (E-B = 284 eV), on a time scale of a few femtoseconds for the first time. The cap ability of detecting x-ray fluorescence excited by few-femtosecond radiatio n with an accuracy of the order of 1 eV paves the way for probing the evolu tion of the microscopic environment of selected atoms in chemical and bioch emical reactions on previously inaccessible time scales (<100 fs) by tracin g the temporal evolution of the "chemical shift" of peaks associated with i nner-shell electronic transitions in time-resolved x-ray fluorescence and p hotoelectron spectra.