Ionization behavior of molecular hydrogen in intense laser fields: Influence of molecular vibration and alignment

Abstract

The alignment-and internuclear-distance-dependent ionization of H 2 exposed to intense, ultrashort laser fields is studied by solving the time-dependent two-electron Schrödinger equation. In the regime of perturbative few-photon ionization, a strong dependence of the ionization yield on the internuclear distance is found. While this finding confirms a previously reported breakdown of the fixed-nuclei approximation for parallel alignment, a simpler explanation is provided and it is demonstrated that this breakdown is not due to vibrational dynamics during the laser pulse. The persistence of this effect even for randomly aligned molecules is demonstrated. Furthermore, the transition from the multiphoton to the quasistatic (tunneling) regime is investigated considering intense 800 nm laser pulses. While the obtained ionization yields differ significantly from the prediction of Ammosov-Delone-Krainov rates, we find a surprisingly good quantitative agreement after introducing a simple frequency-dependent correction to the standard tunneling formula.

Photoionization of few electron systems: a hybrid coupled channels approach

“…Figure 8 shows total ionization yield as a function of photon energy in the range 0.17-0.5 a.u. Results from haCC are compared with data available from other theoretical methods-time-dependent CI method from [35] and FNA-TDSE (fixed nuclei approximation) method from [7]. In addition, several points from our tSURFF- based full-2e method are included.…”

“…(table 1 in [36]),the ionization potential in [35] is 0.590 36 a.u., whereas in our calculations we obtain 0.6034 a.u. Also note that the results in [35] were shifted by 0.0092 a.u. in energy to match the resonance at 0.46 a.u.…”

Non-resonant dynamic stark control of vibrational motion with optimized laser pulses

“…The temporal standard deviation of the Gaussian smoothing kernel was set to 1 fs, and the intensity limit of the pulse envelope was set to 30 TW/cm 2 , which was estimated to be low enough as to not cause any appreciable system ionization using the FC-ADK tunneling ionization model. 47 Using these parameters, the genetic algorithm was able to achieve ∼99% population transfer from the ground to second vibrational state of the HCl molecule after 346 generations with a population size of 2000 individuals. The full intensity profile of the optimized pulse envelope is shown in Fig.…”

“…The motivation behind this choice is traced to the fact that at the frequencies we are considering, it can be shown that limiting the peak intensity is of critical importance when it comes to diminishing unwanted ionization effects, whereas changes in the pulse fluence have been shown to be less impactful in this respect. [44][45][46][47] If we choose to change the parameters of our analysis by instead keeping the pulse energy constant, it would not be possible to calculate a non-trivial optimal pulse width like the one in Eq. (24).…”

Imaging of the umbrella motion and tunneling in ammonia molecules by strong-field ionization

“…This orientation has been already experimentally realized and variation of the orientation did not reveal contributions to the ionization from lower lying orbitals [5]. The TDSE ionization yields are compared to the ones obtained using Ammosov-Delone-Krainov (ADK) tunneling rates Γ ADK [14,15] and the recently introduced frequency-corrected ADK (FC-ADK) model [18] based on the Perelomov-Popov-Terent'ev (PPT) [13] theory. By integrating the tunneling rate over the whole pulse duration, one obtains the ionization yield…”