Ultrafast Nonlinear Carrier Dynamics in n-Doped Ge at High Field Strengths

Ultrafast carrier dynamics in n-doped Ge is investigated by THz pump—THz probe spectroscopy with pump THz field strengths up to <0.45 MV/cm provided by a user-accessible compact nonlinear THz spectroscopy facility at ELI-ALPS. The saturation and recovery of the free-carrier absorption is observed on picosecond time scale at 300 K and 95 K temperatures. Furthermore, the intensity-dependent modulation of the refractive index is also observed.