Optically tuned dielectric characteristics of SrTiO3/Si thin film in the terahertz range

Active control of the optical parameters in strontium titanate (SrTiO3, STO) thin films is highly desirable for tunable terahertz (THz) integrated devices such as filters, phase modulators, and electro-optical devices. In this work, optically tuned dielectric parameters of a STO thin film epitaxially grown on a silicon wafer were characterized in the THz region with an 800 nm laser pump-THz detection system. The refractive index, extinction coefficient, and complex dielectric constant of the STO thin film were calculated using thin-film parameter extraction. Owing to carrier transportation and soft-mode oscillation, the above optical parameters change notably with the pump power of the external laser. This study is of great significance for rapid and non-contact THz phase-modulation technology and may serve as a powerful tool to tune the dielectric properties of the STO thin films.