All-optical generation and detection of sub-picosecond ac spin current   pulses in GaAs
  Sub-picosecond ac spin current pulses are generated optically in GaAs bulk and quantum wells at room temperature and 90K through quantum interference between one-photon and two-photon absorptions driven by two phase-locked ultrafast laser pulses that are both circularly polarized. The dynamics of the current pulses are detected optically by monitoring in real time and real space nanoscale motion of electrons with high-resolution pump-probe techniques. 
Brian A. Ruzicka, Karl Higley, Lalani K. Werake, and Hui Zhao