Photoelectron spectra and high Rydberg states of lithium generated by intense lasers in the over-the-barrier ionization regime

Abstract

We calculated photoelectron energy and momentum spectra and the population of high Rydberg states of lithium atoms by intense 785 nm laser pulses at intensities in the over-the-barrier ionization (OBI) regime. The calculated spectra are compared to experiments reported in Schuricke et al. [Phys. Rev. A 83, 023413 (2011)]. It is shown that in the OBI regime, due to strong depletion of the ground state, the photoelectron spectra are generated from the leading edge of the laser pulse only, resulting in spectra that are nearly independent of laser intensities. Analysis of the calculated spectra reveals that total ionization probability is suppressed as the intensity is increased in the OBI regime. The suppression is due to the increase of excitation probability of high Rydberg states in the OBI regime, demonstrating that atoms and molecules are never fully ionized at high intensities. We also conclude that the interference stabilization model is not needed to explain the formation of high Rydberg states, and that there is no evidence that laser-dressed Kramers-Henneberger states play a role in the strong-field ionization of atoms and molecules by infrared lasers in the OBI regime.

Absolute strong-field ionization probabilities of ultracold rubidium atoms

“…Consequently, one has to rely on calculating the ionization process with TDSE methods. Our results underline the dominance of multiphoton ionization in alkali atoms consistent with previous experiments [20][21][22] and theory [30,31].…”

“…For rubidium this over-the-barrier (OBI) intensity is reached at I OBI = 1.22 × 10 12 W/cm 2 (vertical black dashed line). Previous experiments [20,22] and theoretical studies [30,31] have already mentioned the peculiar situation that in alkali atoms the OBI intensity is reached well within the multiphoton regime, in particular for rubidium at a Keldysh parameter of γ = 8.4 for an optical wavelength of 511 nm (compare Fig. 3a).…”

Photoionization of few electron systems: a hybrid coupled channels approach

“…It has been shown through examples in section 4.1 that helium can be modeled as single channel system at longer wavelengths. Lithium, the smallest alkali metal, also has been successfully modeled as a single electron system in an effective potential, for example in [30]. We find that beryllium needs at least two ionic states, 1s 2s 2 and 1s 2p 2 , for a realistic modeling.…”

Two-color XUV+NIR femtosecond photoionization of neon in the near-threshold region

“…In our calculations the splitting can be seen not only in sidebands, but also in the main line. Analogous splitting of ATI peaks is a well-known fact confirmed both experimentally [15][16][17] and theoretically [17][18][19]38]. The first observation of a narrow fine structure of the individual ATI peaks was reported by Freeman et al [16] for subpicosecond laser pulses.…”

“…We note that there is a certain similarity between near-threshold two-color XUV+NIR ionization and onecolor above-threshold ionization (ATI) by a strong NIR laser field. Thus ATI calculations and experiments have observed similar effects such as the angular dependence of the ATI peak intensity [14,15] as well as the splitting of the ATI peaks at low energy [15][16][17][18][19]). However, due to the highly nonlinear nature of the process, and the fact that in addition resonant multiphoton processes are involved, the ATI case is much more complex to interpret.…”