Dynamics and coherence of resonant X-ray Raman scattering

Although truly time-resolved measurements, which are now standard in optical laser spectroscopy, have not hitherto been possible to carry out for resonant X-ray scattering processes (RXS), there is still in principle the possibility of obtaining indirect information on the time-dependent dynamics of RXS, namely on a time-scale set by the inverse of the detuning frequency, i.e. a frequency between the excitation and the X-ray absorption resonance maximum. This idea has recently been realized by introducing the concept of a duration time of the RXS process, which can be varied with the help of the excitation frequency. This concept has turned out to be powerful from the point of view of time selection and active operation on microscopic processes with different time scales. At the present time, several dynamic effects in RXS have been discovered. We describe here the current state of investigations of these dynamic effects which are controlled by the variation of the excitation frequency.