The nonlinear optical properties of semiconductor quantum wells driven by intense in-plane
terahertz electric fields are investigated theoretically by employing the extended semiconductor
Bloch equations. The dynamical Franz-Keldysh effect of the optical absorption near the band edge
is analyzed with Coulomb correlation among the carriers included. The in-plane terahertz field
induces a variety of behavior in the absorption spectra, including terahertz replicas of the (dark) 2p
exciton and terahertz sidebands of the 1s exciton. The dependence of these interesting features on
the intensity, frequency, and phase of the terahertz field is explored in detail.