Distinct contribution of acoustic and optical phonons in light-induced lattice transformation was resolved at different time scales by monitoring the insulator-to-metal phase transition in epitaxial and nonepitaxial ${\mathrm{VO}}_2$ films. Applying the ultrafast angle-resolved light scattering technique we demonstrate a significant influence of internal misfit strain in epitaxial films on subpicosecond phase transition dynamics. This technique also allows for observing a contribution of structural defects in the evolution of the transient state. The ultrafast structural phase transition dynamics is discussed in terms of the Ginzburg-Landau formalism. Using a set of experimental data we reconstruct the thermodynamic potential of photoexcited ${\mathrm{VO}}_2$ and provide a phenomenological model of the ultrafast light-induced structural phase transition.

• Received 6 February 2017
• Revised 27 July 2017

DOI:https://doi.org/10.1103/PhysRevB.96.075128