Nonlinear spectroscopy using intense THz pulses with amplitudes exceeding 1 MV/cm

This talk focused on THz nonlinear optical phenomena in semiconductors using intense THz pulses with amplitudes exceeding 1 MV/cm. Strong spectral modulations in the heavy-hole and light-hole exciton absorption band in ZnSe/ZnMgSSe multiple-quantum-well (MQW) structure induced by intense THz electric field are observed. The peak-shift of exciton absorption clearly indicates deviation from the Stark effect, which implies that the interaction between exciton and THz wave enters the non-perturbative regime. These results indicate that AC Stark effect and dynamical Franz Keldysh effect should be competed in this field strength around E_THz = 10 KV/cm.