  We report on the time-resolved detection of the anomalous velocity,
constituting charge carriers moving perpendicular to an electric driving field,
in undoped GaAs quantum wells. For this we optically excite the quantum wells
with circularly polarized femtosecond laser pulses, thereby creating a state
which breaks time-inversion symmetry. We then employ a quasi single cycle
terahertz pulse as electric driving field to induce the anomalous velocity. The
electromagnetic radiation emitted from the anomalous velocity is studied with a
sub-picosecond time resolution and reveals intriguing results. We are able to
distinguish between intrinsic (linked to the Berry curvature) and extrinsic
(linked to scattering) contributions to the anomalous velocity both originating
from the valence band and observe local energy space dependence of the
anomalous velocity. Our results thus constitute a significant step towards
non-invasive probing of the anomalous velocity locally in the full
energy/momentum space and enable the investigation of many popular physical
effects such as anomalous Hall effect and spin Hall effect on ultrafast time
scales.
