  In (100)-oriented GaAs illuminated at normal incidence by a laser and its
second harmonic, interference between one- and two-photon absorption results in
ballistic current injection, but not modulation of the overall carrier
injection rate. Results from a pump-probe experiment on a transversely biased
sample show that a constant electric field enables coherent control of the
carrier injection rate. We ascribe this to the nonlinear optical Franz-Keldysh
effect and calculate it for a two-band parabolic model. The mechanism is
relevant to centrosymmetric semiconductors as well.
