Terahertz emission from photoexcited surfaces of Ge crystals

The mechanism of terahertz emission from the surfaces of n- and p-type Ge crystals illuminated by femtosecond Ti:sapphire laser pulses was investigated. It has been concluded that this emission is caused by the cold plasma oscillation activated by a transient polarization arising due to different diffusion rates for photoexcited electrons and holes. The dynamics of those carriers was also investigated with subpicosecond temporal resolution by using an optical pump-terahertz probe technique.