Theory and Modelling of Ultrafast X-ray Imaging of Dynamical Non-equilibrium Systems

Over the next few years, a new generation of x-ray sources is going online. These freeelectron lasers will provide extremely bright subpicosecond x-ray pulses. Traditionally, x-ray diraction has the advantage of directly determining the atomic positions within a sample. With these new machines, it becomes feasible to exploit this concept for ultrafast processes; in eect, we can study chemical reactions as they occur. This thesis deals with theoretical aspect of ultrafast time-resolved x-ray diraction (TRXD).We derive general formulas for calculating the diraction signal that are closely related to those encountered in time-independent diraction. We also specify the approximations that are required to obtain these formulas, and embed the technique of TRXD in the wider frame of time{domain pump{probe experiments for the study chemical reactions. Furthermore, we study new opportunities arising in the context of TRXD. We give a detailed treatment of the anisotropies that persist after exciting molecules with an optical pump laser, and specify how to setup an experiment and analyze the diraction patterns in an optimal way.