Abstract

We present the results of two calculations on the above-threshold ionization of one-electron atoms. In the first calculation, the 3-D Schrodinger equation is solved numerically. It is assumed that the pulse has a Gaussian shape and a duration of three optical cycles (FWHM). To make the classical comparison, the initial hydrogenic bound state is modeled as an ensemble of classical electrons satisfying approximately the same distribution in position and momentum as the initial quantum state. Newton's equation is solved numerically for the time evolution of the ensemble. Of particular interest is the electron’s energy spectrum at the end of the pulse. Classically it is found that the spectrum is always intensity dependent. The quantum mechanical spectrum acquires the intensity dependence characteristic of classical electrodynamics in the limit in which many photons are absorbed, i.e., in the case of ATI. We show that some of the features of ATI may be explained very simply in the classical picture and discuss some of the ways in which the classical correspondence fails.

© 1987 Optical Society of America