Time-resolved observation of dynamical Franz-Keldysh effect under coherent multi-cycle terahertz pulses

The nonlinear interaction of matter with strong, oscillating electric fields has attracted considerable attention from the perspective of fundamental physics and technological applications such as electro-optic devices. One of the most remarkable electric field effects of dielectric materials under a static electric field is the Franz-Keldysh effect (FKE). The theoretical extension of the FKE to time-dependent electric fields can be described as a non-perturbative effect, i.e., the dynamical FKE (DFKE). Intensive experimental studies have been performed with narrow-band THz pulses from free-electron lasers and have shown a blueshift in the excitonic absorption peak caused by the DFKE [1,2]. On the other hand, recent advances in Ti: sapphire-based THz laser systems generating phase-stable transients with a femtosecond timing accuracy may give us complementary information on the fundamental characteristics of the DFKE [2-4], which cannot be obtained with time-averaged measurements.