Laser-induced ultrafast structural transformations in thin Fe layer revealed by time-resolved X-ray diffraction

The ultrafast structural response of a thin iron film to sub-ps pulsed laser-induced heating has been investigated using time-resolved X-ray diffraction in the partial melting regime. A tetragonal distortion of the bcc-phase emerges at ~6 ps. Its formation is delayed relative to the initial heating (1-2 ps) and partial melting (2-5 ps) of the material, and controlled by the stress release in the quasi-instantaneously pressurized film. The distortion persists for at least 60 ps indicating the formation of a metastable bct phase between the equilibrium bcc and fcc phases.