State of the art and opportunities in probing photoinduced phase transitions in molecular materials by conventional and picosecond X-ray diffraction

Abstract

The optical control of the macroscopic physical properties (magnetic, optical …) of a material by laser irradiation is gaining interest through the emerging field of photoinduced phase transitions. Light-induced changes of the macroscopic state of a material involves subtle coupling between the electronic and structural degrees of freedom, which are essential to stabilize the photo-excited state, different in nature from the stable state. Therefore the new experimental field of photocrystallography plays a key role. It goes far beyond simple structural analysis under laser excitation. By playing on different physical parameters and developing the techniques and analysis, one can investigate new out of equilibrium physics through light-driven cooperative dynamics and transformations in materials. This paper is reviewing different aspects of the use of photocrystallography to investigate the nature, the mechanisms and the dynamics of photoinduced phase transitions for photo-steady or long-lived states, as well as transformations driven by an ultra-short light pulse. We also give a brief overview on recent advances in time-resolved crystallography with 100 ps resolution.