Comparison of two forms of the S-matrix element of strong-field photoionization: II. (n, l, m) = (2, 1, ±1) states

摘要

In our previously published work (Bauer 2008 J. Phys. B: At. Mol. Opt. Phys. 41 185003) we numerically compared ionization rates and photoelectron energy (or momentum) spectra resulting from the so-called length gauge (LG) and velocity gauge (VG) forms of the Keldysh-Faisal-Reiss theory for a strong circularly polarized laser field. Our investigations concerned initial (bound) states of a hydrogen atom with the principal quantum number equal to 1 or 2. However, some of these states were not taken into account in this work, but only their linear combinations (quantum-mechanical superpositions). The main purpose of the present work is to fill this gap. It is appropriate to add that excited bound states (of the hydrogen atom) considered here are easier to achieve from an experimental point of view. As in our previous work, we find substantial differences in the shape of photoelectron energy spectra for both (LG and VG) theories. Differently from the VG theory, the LG one shows a multipeak envelope in photoelectron energy spectra for most initial states of the hydrogen atom. We give examples showing that the multipeak effect may be observed also in the polarization plane of the laser field. The field parameters (frequency and intensity) applied by us in the calculations indicate that one should be able to observe experimentally the above-mentioned effect in the near future.