Light-Induced Functional VO<sub>2</sub> Films

Abstract

Ultrafast optical pump-probe technique employed in a degenerate-four-wave-mixing configuration was used to study the light-induced optical property change during extremely short time period of femtoseconds (fs) to picoseconds (ps) for VO2 thin films. Dramatic change in optical properties serves as basis of light-induced functional materials in ultrafast applications. Upon light illumination the structural change was identified as a phase transition (PT) from insulator to metallic phases. After the light-induced PT a fast recovery process occurred, which was strongly dependent on optical pump energy. It could be governed by pure electronic relaxation excluding thermal contribution at sufficiently low excitation. The insulator and metallic phases are coexistent exhibiting fluctuations of dielectric constants. Different desorption activity was monitored for insulator and metallic VO2 thin solid films under femtosecond optical excitation.