Vanadium Oxide (VO2)

Several vanadium oxides change their properties with temperature due to a crystallographic phase change between monoclinic (insulator) and tetragonal (metal) symmetry. Among them VO2 is the most studied, because the transition happens at 68°, very close to room temperature. For the effect of the phase transition, both electrical and optical properties undergo a strong change.
Recently, we have demonstrated that it is possible to use a VO2 layer to convert mid-IR wavelength to NIR wavelength detectable with silicon cameras such as CCD and CMOS. We used a mid-IR beam (called writing beam or pump beam) to locally change the reflectivity in the VO2 layer. This reflectivity change depends on the local temperature, which is related to the intensity of the writing beam, and it is extended from the NIR to the mid-IR. Thus a second beam in the NIR compatible with CCD and CMOS technology (called reading beam or probe beam) is used for the detection of the reflectivity pattern imposed by the writing beam.