Characterization of carrier-envelope phase-sensitive photocurrent injection in a semiconductor

We characterize the manner in which the carrier-envelope phase of ultrashort pulses can control quantum interference of injected photocurrents in low-temperature-grown gallium arsenide. We verify the predicted linear and square-root dependences of the generated current on the average optical powers of the low (nu) and high (2nu) frequency wings of a pulse spectrum, respectively. When scanning the time delay between these two colors, the signal amplitude exhibits a temporal width of 72 fs. The generated signal behaves as an ideal current source for loads below ∼100 kOmega. This behavior allows us to increase the signal detection bandwidth from 25 kHz with a voltage amplifier to 830 kHz by use of a transimpedance amplifier; higher bandwidths are possible. We discuss how transimpedance amplification could also enable the quantum-interference photocurrent signal to be measured by use of materials with longer carrier lifetimes, such as intrinsic GaAs.