THz emission from coherently controlled currents in GaAs

Summary form only given. Coherence control (CC) makes use of the phase of optical beams to alter the properties of matter via interference of quantum mechanical pathways. Earlier it was shown that CC electrical currents can be generated in GaAs and LT-GaAs at 295 K by interfering single and two photon transition amplitudes coupling the same valence and conduction band states. The current temporal profile is expected to follow the optical pulse envelope before decaying to zero on a subpicosecond time scale due to relaxation effects. However in Ref. 1 time-integrated photocurrents were measured using a train of femtosecond pulses and a metal-semiconductor-metal charge collector. Here we report observation of THz radiation from the transient currents. CC currents permit tailoring of THz radiation through the bandwidth of optical pulses, e.g., producing single cycle high frequency radiation and overcoming limitations of biased antenna emitters. The radiation is also a diagnostic of intraband coherence dynamics of nonequilibrium carriers.