The control of condensed matter systems out of equilibrium by laser pulses
allows us to investigate the system trajectories through symmetry-breaking
phase transitions. Thus the evolution of both collective modes and single
particle excitations can be followed through diverse phase transitions with
femtosecond resolution. Here we present experimental observations of the order
parameter trajectory in the normal-superconductor transition and charge-density
wave ordering transitions. Of particular interest is the coherent evolution of
topological defects forming during the transition via the Kibble-Zurek
mechanism, which appears to be measurable in optical pump probe experiments.
Experiments on CDW systems reveal some new phenomena, such as coherent
oscillations of the order parameter, the creation and emission of dispersive
amplitudon modes upon the annihilation of topological defects, and mixing with
weakly coupled finite-frequency (massive) bosons
