Quantum interference control of electrical currents in GaAs microstructures: physics and spectroscopic applications

We present a comprehensive study of coherently controlled charge currents in electrically contacted GaAs microdevices. Currents are generated all-optically by phase-related femtosecond \(\omega /2\omega\) pulse pairs and are often linked to the third-order optical nonlinearity \(\chi ^{(3)}(0;\omega ,\omega ,-2\omega )\). Here, we first focus on elevated irradiances where absorption saturation and ultimately the onset of Rabi oscillations contribute to the optical response. In particular, we identify clear departures of the injected current from the \(\chi ^{(3)}\)-expectation \({\mathrm {d}}J/{\mathrm {d}}t \propto E_\omega ^2 E_{2\omega }\). Theoretical simulations for the coherently controlled current based on the semiconductor Bloch equations agree well with the experimental trends. We then move on to investigate spectroscopic applications of the quantum interference control technique. In particular, we implement a versatile scheme to analyze the phase structure of femtosecond pulses. It relies on phase-sensitive \(\chi ^{(3)}\)-current injection driven by two time-delayed portions of the \(\omega\)/\(2\omega\) pulse pair. Most strikingly, the group velocity dispersions of both the \(\omega\) and \(2\omega\) components can be unambiguously determined from a simple Fourier transform of the resulting current interferogram. Finally, we aim to use femtosecond \(\omega /2\omega\) pulse pairs to demonstrate a theoretically proposed scheme for all-optical current detection in thin GaAs membranes. However, we find the signal to be superimposed by second harmonic generation related to the electric field inducing the current. As a result, the currents’ signature cannot be unambiguously identified.