All-optical generation and detection of subpicosecond ac spin-current pulses in GaAs

Abstract

Subpicosecond ac spin-current pulses are generated optically in GaAs bulk and quantum wells at room temperature and at 90 K 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 in real space, the nanoscale motion of electrons with high-resolution pump probe techniques. The spin polarization of the currents is 0.6Ϯ 0.1, with peak current densities on the order of 10 2 A / m 2 .

Second-Harmonic Generation Induced by Electric Currents in GaAs

“…Such a lag has been confirmed in our previous high-resolution pump-probe experiments, where the charge separation was found to reach a peak after more than 100 fs. [26,27] However, here we observe the peak SHG around zero probe delay. Hence, the all-optical time-resolved technique has the advantage to unambiguously distinguish the field-induced and the current-induced SHG effects.…”

Optical studies of ballistic currents in semiconductors [Invited]

“…The high-resolution pump-probe technique allows us to study the dynamics of the spin-polarized charge currents injected by the QUIC technique [63]. The experiment was performed on a 400 nm bulk GaAs sample at room temperature and a 10-period 14 nm GaAs multiple-quantum-well sample at 90 K. Similar results were obtained from both samples.…”

Spatially resolved femtosecond pump-probe study of topological insulator Bi2Se3

“…A balanced detection technique is used in order to improve the signal-to-noise ratio. 58 The pump and the probe pulses are linearly polarized along perpendicular directions. We have also repeated one measurement with the two pulses polarized along the same direction, and found no difference in the signal.…”