Strong-field phenomena caused by ultrashort laser pulses: Effective one- and two-dimensional quantum-mechanical descriptions

Abstract

In this article, we address two strong-field phenomena which attract much attention and can be observed under similar experimental conditions, namely when a gas is ionized by ultrashort laser pulses. The first phenomenon is the excitation of high-order harmonics of the driving field frequency in the electron current, which leads to the generation of extreme UV and soft-x-ray radiation. The second phenomenon is the excitation of a quasi-dc residual current in the laser-produced plasma, which results in the generation of radiation having a frequency below the laser one, e.g., THz waves. We present alternative one- and two-dimensional quantum-mechanical models for the description of such phenomena for the gas consisting of H atoms and the generalization of these models to the various noble gases. The shape of the electrostatic potential produced by an atomic ion is shown to influence significantly the rates of the processes in the dynamics of atomic electron and, even more, the rate of tunneling ionization, which is of utmost importance for the considered phenomena. The results of solving the time-dependent Schr\odinger equation with the proposed model potentials are compared with the results of the ab initio three-dimensional calculations for the H atom. We find that in a wide range of laser pulse parameters the results obtained with proposed models have much better accuracy than the results provided by the models used earlier.