Ratios of double to single ionization of He and Ne by strong 400-nm laser pulses using the quantitative rescattering theory

Abstract

We present numerical simulations of the ratio between double and single ionization of He and Ne by intense laser pulses at wavelengths of 390 nm and 400 nm, respectively. The yields of doubly charged ions due to nonsequential double ionization (NSDI) are obtained by employing the quantitative rescattering (QRS) model. In this model, the NSDI ionization probability is expressed as a product of the returning electron wave packet (RWP) and the total scattering cross sections for laser-free electron impact excitation and electron impact ionization of the parent ion. According to the QRS theory, the same RWP is also responsible for the emission of high-energy above-threshold ionization (HATI) photoelectrons. To obtain absolute double-ionization yields, the RWP is generated by solving the time-dependent Schrödinger equation (TDSE) within a one-electron model. The same TDSE results can also be taken to obtain single-ionization yields. By using the TDSE results to calibrate single ionization and the RWP obtained from the strong-field approximation, we further simplify the calculation such that the nonuniform laser intensity distribution in the focused laser beam can be accounted for. In addition, laser-free electron impact excitation and ionization cross sections are calculated using the state-of-the-art many-electron R-matrix theory. The simulation results for double to single ionization ratios are found to compare well with experimental data and support the validity of the nonsequential double ionization mechanism for the covered intensity region.

Pulse-duration dependence of the double-to-single ionization ratio of Ne by intense 780-nm and 800-nm laser fields: Comparison of simulations with experiments

“…With these carefully evaluated TCSs, we were able to simulate the ratio of Ne 2+ /Ne + yields as a function of peak intensity in a 40 fs pulse with a wavelength of 400 nm. Indeed, the calculated results are in very good agreement with experiment [17].…”

“…The theoretical model used in this paper to simulate the double-to-single ionization ratio for atoms in linearly polarized laser pulses was presented in detail in [15,17]. Hence we only give a brief review here.…”

“…It was also demonstrated that the PPT model is fully capable of reproducing single ionization probabilities for atoms in laser fields from the multiphoton to the tunneling ion-ization regimes [24]. While the SFA1 model was used in [15,17], in the present paper we employ the improved PPT model to calculate the single ionization yield for Ne atoms.…”

“…To calculate the total nonsequential double ionization yields, we employ the improved quantitative rescattering (QRS) model [15,17], in which the lowering of the required energy for electrons to escape from the nucleus at the time of recollision, due to the presence of an electric field, is taken into account. The QRS model was first proposed for high-order above-threshold ionization (HATI) attributed to elastic scattering of the returning electron from the parent ion [25].…”

Restricted-space ab initio models for double ionization by strong laser pulses

“…On the other hand, such a ratio allows for a quantitative comparison with experiment since volume averaging effects (due to laser intensity variation across the sample) while affecting strongly the yields themselves may modify this ratio by a factor of two at most. Both the experiment [7] and theory [51,53,54] give the saturation value of He 2+ /He + being of the order of 10 −3 , an order of magnitude smaller than the ratio obtained for ES model, and almost two orders smaller than this ratio in CM model (compare Fig. 5).…”