Optical-to-THz radiation conversion on a semi-metal surface

We consider the possibility of generation of broadband terahertz (THz) radiation upon reflection of a p-polarised femtosecond laser pulse from the surface of a semi-metal. The hydrodynamic model of an instantaneous quadratic response of metals is generalised, and analytical results and numerical simulation data are presented. It is shown that transition from highly conductive metals to semi-metals is accompanied by a significant increase in the efficiency of the THz signal generation due to the reduction of the effective charge carrier mass and attenuation of the shielding of optical and THz fields.