  An ultrafast anisotropic electro-optic effect of the zinc sulfide crystal is
predicted employing a numerical pump-probe simulation. The numerical results
indicate that the time-dependence of the anisotropic response of ZnS exhibits a
phase shift with respect to the pump laser field. The phase shift coincides
with the time-resolved dynamical Franz-Keldysh effect, which is the modulation
of the isotropic part of the dielectric function. While the probe frequency
dependence around the band gap is not intense, it becomes intense at higher
photon energies of approximately 42~eV.
