  We predict a strong-field ultrafast optical Faraday effect, where a
circularly polarized ultrashort optical pulse induces transient chirality in an
achiral transparent dielectric. This effect is attractive for time-resolved
measurements because it gives access to the non-instantaneity of the nonlinear
medium response, and also because it represents relaxation of time-reversal
symmetry by all-optical means. We propose probing the induced transient
chirality with a weak linearly polarized ultraviolet pulse that is shorter than
the near-infrared pump pulse. The predicted effects are ultrafast: the induced
chirality vanishes for probe delays exceeding the duration of the near-infrared
pulse. This opens up possibilities for applications in ultrafast
circular-polarization modulators and analyzers.
