Using two-color optical coherence control techniques in intrinsic GaAs at 80 K with orthogonally polarized 70 fs, 1430 and 715 nm pulses, we generate a pure spin source current that yields a transverse Hall pure charge current; or alternatively, with parallel polarized pulses, we generate a pure charge source current that yields a pure spin current. By varying the relative phase or polarization of the incident pulses, one can effectively tune the type, magnitude and direction of both the source and transverse currents without application of electric or magnetic fields.

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Ballistic pure spin currents are injected into Ge at 295 K using quantum interference between one and two photon absorption processes for 1786 and 893 nm, 200 fs optical pulses. The spin currents are spatially and temporally detected using polarization-and phase-dependent differential transmission techniques with nanometer spatial and femtosecond temporal resolution. We interpret the dynamics in terms of the fast spin relaxation of the holes and intervalley transfer of electrons.

The dynamics of charge currents ballistically injected in GaAs bulk and quantum wells are spatially and temporally resolved. The electrons and holes are injected with oppositely directed velocities without the use of accelerating fields by quantum interference between two photon absorption of a 200fs, 1430nm fundamental pulse and one photon absorption of the corresponding second harmonic pulse. The subsequent charge motion is followed with ∼200fs temporal and ∼1nm spatial resolution by using tightly focused optical differential transmission techniques that are dependent on the relative phase of the incident pump pulses. Initially, the electrons and holes ballistically separate by up to ∼20nm, and a space charge field forms, which decelerates the carriers. Within this ∼1ps regime, the momentum relaxes by electron-hole and phonon scatterings, and the space charge field restores the electrons and holes to a common position; on time scales long compared to 1ps, ambipolar diffusion and recombination complete the return of the system to equilibrium. A rigid shift (damped simple harmonic oscillator) model for the electron motion reproduces the key features in the data, and the procedure for extracting the spatiotemporal dynamics of the electrons is shown to be immune to energy relaxation effects and forgiving of nonlinear saturation.

All optical techniques are used to inject and to study the relaxation dynamics of ballistic charge currents in clean germanium at room temperature without the application of external contacts or the use of externally applied fields. Ballistic currents are injected by the quantum interference between the transition amplitudes for direct one and two photon absorption of a pair of phase-locked and harmonically related ultrafast laser pulses. The transport of carriers following ballistic injection is temporally and spatially resolved using optical differential transmission techniques that are sensitive to the relative optical phase of the two injection pulses. The electron-hole dynamics are determined by the initial ballistic injection velocity, momentum relaxation, and space charge field effects. The injection process in Ge is similar to that in direct band gap materials but the indirect nature of Ge complicates the monitoring of the carrier dynamics, allowing the holes to play a more prominent role than in direct gap materials. The latter opens the possibility of following the hole (as opposed to the electron) dynamics.