Coherent control of ultrafast shift currents in GaAs with chirped optical pulses.

We demonstrate the coherent control of ultrafast shift currents in GaAs with two orthogonally polarized linearly chirped laser pulses. By varying the chirp and phase delay between the pulses, we achieve the control of the shape of the shift current transients in a wide range from a monopolar shape to different bipolar shapes (alternating currents). Moreover, the terahertz emission patterns resulting from the ultrafast shift currents allow one to determine the sign of the chirp of the laser pulses.