Mixed regime of light-matter interaction revealed by phase sensitive measurements of the dynamical Franz-Keldysh effect

Significant changes of the optical properties of semiconductors can be observed by applying strong electric fields capable to modify the band structure at equilibrium. This is known as the Franz-Keldysh effect (FKE). Here we study the FKE in bulk GaAs by combining single cycle THz pumps and broadband optical probes. The experiments show that the phase content of the selected electromagnetic pulses can be used to measure the timescales characteristic for the different regimes of matter-light interactions. Furthermore, the present phase-resolved measurements allow to identify a novel regime of saturation where memory effects are of relevance.