SnSe2-functionalized ultrafast terahertz switch with ultralow pump threshold

Abstract

Integrating a metasurface with photoactive materials provides a unique and promising method to achieve the ultrafast modulation of terahertz (THz) waves. However, less attention has been paid to the practical issues of this method, such as the energy consumption of the laser and the fabrication cost of the material. Focusing on these issues, here we demonstrate an ultrafast THz switch based on a Fano metasurface covered by a 10 nm-thick SnSe₂ film. Interestingly, a modulation depth of 91% is obtained to switch off the Fano resonance under an extremely low pump threshold of 157 μJ cm⁻². To understand this impressive performance, the photoconductivity was calibrated to be 2 × 10⁵ S m⁻¹ by measuring the THz transmission spectra of the pure SnSe₂ film, which is higher than that of most other functional-material candidates. The high photoconductivity ensures that more photogenerated carriers are injected into the metadevice, thereby greatly reducing the laser power requirement. Furthermore, due to the facile processability and low cost of SnSe₂, our strategy offers a practicable scheme in wireless communication, ultrafast pulse shaping and switchable sensing at the THz band.