Quantum-mechanical approach for calculating the residual quasi-dc current in a plasma produced by a few-cycle laser pulse

In this paper, we study the phenomenon of excitation of a residual quasi-dc current in a plasma produced by a few-cycle laser pulse, in the framework of the quantum-mechanical approach based on solving the time-dependent Schroedinger equation for the hydrogen atom. At present, this phenomenon is of interest due to the possibility of using it to convert efficiently few-cycle laser pulses into high-power terahertz waves and to monitor the carrier-envelope phase (CEP) of few-cycle laser pulses. We confine ourselves to considering the laser pulses having relatively weak intensities (∼1014 W cm-2). For such pulses, we find the residual current density as a function of the CEP, and the CEP, which is optimal for the occurrence of the considered phenomenon, as a function of the laser pulse intensity. We compare the results of quantum-mechanical and semiclassical calculations and demonstrate that they agree very well with each other, when the maximum ponderomotive energy of the electron in the laser pulse is much greater than the ionization potential and that they are totally different for the pulses with lower intensities, when this condition is not fulfilled.