Extended Data Fig. 2: Fluence dependence of the transient dynamics.
From: Ultrafast X-ray imaging of the light-induced phase transition in VO2
a Differential signal at 20 ps time delay and 529.5 eV photon energy as a function of fluence. As the fluence increases more domains are switched, until changes rise rapidly around 20 mJ/cm2 and saturate. This saturation is associated to switching all of the domains and the full depth of the bulk. Changes above 24 mJ/cm2 are associated with changes in the initial state rather than dynamics, as shown in panel b. b Pre-time-zero images at 36 mJ/cm2 and 39.6 mJ/cm2, as used in part a. When the fluence is increased the initial domain pattern undergoes an irreversible change. For example, the highlighted region shows the erasure of a vertical stripe domain. This is attributed to X-ray shots with higher than average flux52 c Thermal domain structure measured at the ALBA synchrotron. The domain pattern is similar but exhibits some notable differences, attributable to the rapid cooling cycles in the time-resolved experiment.
