FEMTOSECOND LASER EXCITATION OF THE SEMICONDUCTOR-METAL PHASE-TRANSITION IN VO2

We have measured the subpicosecond optical response of a solid-state, semiconductor-to-metal phase transition excited by femtosecond laser p ulses. We have determined the dynamic response of the complex refracti ve index of VO2 thin films by making pump-probe optical transmission a nd reflection measurements at 780 nm. The phase transition was found t o be largely prompt with the optical properties of the high-temperatur e metallic state being attained within 5 ps. The ultrafast change in c omplex refractive index enables ultrafast optical switching devices in VO2.