Generation of terahertz radiation in thin vanadium dioxide films undergoing metal-insulator phase transition

Generation of terahertz (THz) radiation was observed in epitaxial VO
₂
films grown on R- and C-cut sapphire substrates above and below the metal-insulator phase transition temperature. Polarization analysis of the emitted THz radiation reveals strong in-plane anisotropy of the conductive phase of VO
₂
which is not observed for insulating phase, generation efficiency increases up to 30 times after phase transition. Properties of generated THz radiation in VO
₂
are defined by the displacement photocurrent at the film-air and film-substrate interfaces.