Femtosecond degenerate four-wave mixing in thick semiconductors

We have performed the femtosecond two-pulse self-diffracted four-wave mixing (FWM) experiments for a 500 μm undoped GaAs and a 350 μm undoped InP to have further insight into the FWM singnals in thick semiconductors at far below the band gap. We have observed the third- and fifth-order FWM signals for both samples even in the detuning range of 100-170 meV below the band gap. We have also observed that the pronounced blue-shifts of the spectrally resolved (SR) FWM signals at far below the bands gap, exhibiting that these behaviors do not depend on the material properties and temperature. We have proposed that the FWM signals in thick semiconductors at far below the band gap are contributed by the instantaneously created virtual states by temporal overlap of the excitation laser pulses.