Effective mass dependence in laser-induced absorption of ZnO pumped by mid-infrared laser pulse

The time-resolved laser-induced absorption below the band edge in a ZnO sample is observed in the presence of a strong mid-infrared (MIR) pulse. The laser-induced absorption increases with the pump intensity, but it is different in two directions ([11¯00] and [112¯0] direction). The simulation results demonstrate that this phenomenon is primarily caused by the direction dependence of the reduced effective mass of electron and hole. For smaller reduced effective mass, the number of multi-photon ionization channel becomes larger, the probe photons are more likely to be absorbed and the absorption coefficients is larger, so lower pump intensity is needed for absorption saturation.