Time-dependent multiphoton ionization from the He 1s2s1S metastable state
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Dionissopoulou, S
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Nicolaides, CA
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Mercouris, T
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Using the state-specific expansion approach to the solution of the time-dependent Schrodinger equation, we calculated a number of observables from the response of the He 2(1)S metastable state to strong as well as to weak laser pulses. The photon energies (HBAR omega) were 1 eV, 2 eV, 2.47 eV and 3 eV, and the intensities (I) covered the range from 10(8) W cm(-2) to 10(14) W cm(-2). For the weak intensities, the results are in full accord with the experimental findings of Haberland and co-workers. For the strong intensities, our predictions are of quantitative as well as of qualitative value. They permit conclusions about the fingerprints left on observable spectra by electron correlation, by Rydberg levels and by doubly excited states and about the extent to which high harmonics of short wavelength can be produced as a function of l and omega w when the initial state lies above the ground state. Finally, we argue that calculations of harmonic spectra based on the use of the acceleration form of the dipole operator will produce, in general, unreliable results even when some correlations are accounted for.
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