Ultrafast lattice dynamics in solids probed by time-resolved x-ray diffraction

X-ray scattering techniques have been used for the last one-hundred years to map out the structure of matter, from small-scale molecular systems to bulk solids. In this thesis, these techniques are extended into the time-domain, to observe the dynamics of materials on an atomic length scale in real time. In particular, it is shown how the vibrational modes of a solid can be directly observed. A general technique for performing phonon spectroscopy in the time-domain is developed and described. These techniques are applied to the study of transient states of matter under highly non-equilibrium conditions, near the transition from an ordered to a disordered state. It is also shown how one may extract microscopic information about the coupling between carriers and phonons in a material by directly resolving the transfer of energy between the two subsystems. This is applied specifically to the semiconductor InSb. It is also demonstrated how time-resolved diffraction may be used in conjunction with coherent control techniques to control the evolution of a solid-state material and at the same time, probe the resulting product state of a reaction. One may thus control the x-ray diffraction efficiency of a crystalline system. Finally, preliminary experiments studying the structural dynamics of semiconductor nanocrystals are described.