Abstract
Channel-resolved ionization of helium by laser pulses with a photon energy equal to the energy difference between the ionic ground- and first-excited states, i.e., in the core-resonant scenario, is investigated theoretically for a considered peak intensity of W/. By using the essential-states formalism, we derive analytical expressions for the channel-resolved photoelectron spectra, with the pulse-envelope effects taken into account. To examine the validity of the essential-states approach, we numerically solve the time-dependent Schrödinger equation of a model helium and use the corresponding results as references. The justified analytical estimation of the channel-resolved photoelectron spectra serves as a convenient approach to explore the effects of pulse durations and envelopes. It requires a longer pulse duration to observe the spectral peak splitting in the ionic first-excited-state channel than in the ionic ground-state channel. Ionization by two sequent pulses produces more complicated multipeak structures in the channel-resolved photoelectron spectra than ionization by a single pulse. Studies for the nonzero-detuning cases are also presented, where we propose a general procedure for understanding how the photoelectron spectra are built up.
- Received 5 July 2018
DOI:https://doi.org/10.1103/PhysRevA.98.033404
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