Optical switching in VO2 films by below-gap excitation

We study the photoinduced insulator-metal transition in VO2, correlating its threshold and dynamics with excitation wavelength. In single crystals, switching can only be induced with photon energies above the 670meV gap. This contrasts with the case of polycrystalline films, where formation of the metallic state can be initiated also with photon energies as low as 180meV, which are well below the bandgap. Perfection of this process may become conducive to schemes for optical switches, limiters, and detectors operating at room temperature in the mid-infrared.