Ultrafast photo-induced phase transition in VO2 for single-photon sources

In this work, vanadium dioxide thin polycrystalline films are deposited on silica substrates and several techniques are adopted to characterize the structural and optical properties of the samples, such as the transmittance and the dielectric function. This material, which at room temperature is a transparent semiconductor with a monoclinic structure, undergoes a first-order semiconductor-to-metal phase transition at about 68 °C at ambient pressure, becoming a metal with a tetragonal structure. The metallic state can be obtained and controlled also through the illumination of the sample by sufficiently intense and fast optical radiation. In this thesis, the phase transition is investigated using the pump-probe technique with ultrashort (< 100 fs) laser pulses in the near-infrared region (800 nm). Transient absorption time-resolved measurements allow to study the dynamics of the phenomenon, which can be exploited to actively control the life- time of quantum emitters that are coupled to the layer. Such a similar device is particularly interesting in the field of quantum technologies since it perfectly fits the race towards the realisation of solid-state single-photon emitters, which operate at room temperature and enable to have high bit rates that are fundamental for quantum information processes.