Terahertz radiation mechanism from femtosecond-laser-irradiated InAs (100) surface

Terahertz (THz) radiation mechanism from femtosecond-laser-irradiated InAs surface is investigated by measuring the excitation-fluence dependence of THz-radiation power. It is found that the THz-radiation is mainly generated by the surge-current, which originates from the different diffusion velocities between photoexcited electrons and holes. Furthermore, it is also found that the excitation fluence dependence of THz-radiation is categorized into two regions depending on the excitation fluence. At low excitation fluence, a quadratic-dependent enhancement of the THz-radiation power is observed with increasing excitation fluence. In contrast, at high excitation fluence, the enhancement factor is gradually reduced, and the radiation power becomes proportional to a logarithm function of the excitation fluence. These results are explained by considering the photo-Dember field as the THz-radiation source.