TIME-DEPENDENT QUANTUM FLUID-DYNAMICS OF THE PHOTOIONIZATION OF THE HE ATOM UNDER AN INTENSE LASER FIELD

A time-dependent (TD), nonperturbative quantum fluid density functiona l equation of motion, developed in our laboratory, is numerically solv ed for studying the photoionization dynamics of the He atom under an i ntense, ultrasharp, ultrashort laser pulse. The generalized nonlinear Schrodinger equation is obtained through a hydrodynamical continuity e quation and an Euler-type equation of motion. It yields the electron d ensity, effective potential surface, and other density-based quantitie s from start to finish. Starting from the ground-state Hartree-Fock de nsity for He at t = 0, various singlet and triplet states of singly an d doubly excited (autoionizing) He as well as several states of He+ ha ve been identified in the time-evolved electron density, by a Fourier transformation of the time variable of the complex autocorrelation fun ction. Computer visualizations of the TD difference density and differ ence potential show distinctly nonlinear and extremely interesting geo metrical features of the oscillating atom. Detailed mechanistic routes for multiphoton, sequential, and above-threshold ionization have been obtained, each route involving many states. The present, comprehensiv e method reveals the important physical features of the atom-laser int eraction and the calculated results are consistent with current experi mental and theoretical results. This emphasizes the validity of the hy drodynamical approach for studying TD quantum mechanical phenomena. (C ) 1995 John Wiley & Sons, Inc.