We present a time-dependent generalized pseudospectral (TDGPS) approach in {\em hyperspherical coordinates} for fully {\em ab initio} nonperturbative and high-precision treatment of multiphoton electron-correlated dynamics of atomic systems in intense laser fields [1]. The procedure is applied to the investigation of high-order-harmonic generation (HHG) of helium atoms in ultrashort laser pulses at a KrF wavelength of 248.6 nm. The 6D coupled hyperspherical-adiabatic-channel equations are discretized and solved efficiently and accurately by means of the TDGPS method. The effects of electron correlation and doubly excited states on HHG are explored in detail. A HHG peak with Fano line profile is identified which can be attributed to a broad resonance of doubly excited states. Comparison of the HHG spectra of the {\em ab initio} two-electron and the single- active-electron model calculations is also presented. \vspace{1mm} \noindent [1] X. Guan, X.-M. Tong, and S. I. Chu, Phys. Rev. A (in press).
This work was supported by the
Chemical Sciences, Geosciences and Biosciences Division,
Office of Basic Energy Sciences,
Office of Science, U.S. Department of Energy.
Submitted to DAMOP, May 2006 in Knoxville, TN.
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