Femtosecond x-ray and visible pulses were used to probe structural and electronic dynamics during an optically driven, solid-solid phase transition in ${\mathrm{VO}}_2$. For high interband electronic excitation $(\sim 5\times {10}^{21}{\mathrm{cm}}^{-3\mathrm{}})$, a subpicosecond transformation into the high- $T$, rutile phase of the material is observed, simultaneous with an insulator-to-metal transition. The fast time scale observed suggests that, in this regime, the structural transition may not be thermally initiated.

• Received 1 March 2001

DOI:https://doi.org/10.1103/PhysRevLett.87.237401