Intense field stabilization in circular polarization: Three-dimensional time-dependent dynamics

Abstract

We investigate the stabilization of a hydrogen atom in circularly polarized laser fields. We use a time-dependent, fully three dimensional approach to study the quantum dynamics of the hydrogen atom subject to high intensity, short wavelength laser pulses. We find enhanced survival probability as the field is increased under fixed envelope conditions. We also confirm wavepacket dynamics seen in prior time-dependent computations restricted to two dimensions.PACS numbers: 32.80. Fb,32.80.Wr,42.50.Hz The advent of lasers producing electric fields at or above inter-atomic electric fields has led to the discovery of many new and highly nonlinear phenomena [1]. As nonlinear laser-atom physics has matured, computational approaches employed by researchers in the field have naturally been applied to scenarios not easily realized in experiments. One such scenario is the interaction of an intense, high frequency laser with the single-electron hydrogen atom. Commercially available pulsed laser systems readily produce intensities at or above the atomic unit I = 3.51 × 10 16 W/cm 2 , but available photon energieshω are well below the atomic unit frequency, which is given by the ground state ionization energy |E o |. In the case where the driving frequency is near or above the ground state ionization energy,hω ≥ |E o |, a remarkable phenomena known as "stabilization" may occur. Stabilization is characterized by a decrease in the ionization probability as the laser intensity increases. For constant driving field, stabilization is manifest as an increase in dressed state lifetime. However, due to the initial increase in ionization rate for increased fields as the interaction turns on, increased steady-state lifetimes do not necessarily translate into increased end-of-pulse survival probabilities. This poses a significant challenge to experimental observation of stabilization and is commonly known as the "death-valley" problem.Nevertheless, indications of stabilization have been seen by tailoring the initial state to act as an effective ground state [2][3][4][5]. In particular, the high frequency condition has been realized using dipole forbidden circular Rydberg states (n = 4, 5) of neon (|E o | < 1eV ), and a driving laser ofhω = 2eV [2]. In this experiment, a decrease in total ionization yield was observed with increasing peak laser intensity, while fluence was held constant [3]. Fermi's golden rule predicts the total ionization depends only on the fluence, so this result clearly indicates non-perturbative stabilization [4,5]. With this notable exception, however, stabilization remains experimentally unconfirmed, and detailed studies have been confined to the realm of simulation.The vast majority of these studies have concentrated on the case of linearly polarized (LP) fields, where much has been learned about the dynamics of stabilization [6]. Studies considering the case of circularly polarized (CP) fields have also noted comparable or enhanced stabilization [7][8][9][10]. However, the physical mechanism for stabilization...

Two-color stabilization of atomic hydrogen in circularly polarized laser fields

“…The overlayed black circle of radiusα = 10 indicates the corresponding free electron trajectory. A clockwise "hula-hoop"-like [11] dynamics of the probability density ring is observed.…”

“…This, at first sight, counterintuitive effect is called dynamic or adiabatic stabilization, depending on the pulse length [1,2,3,4,5,6,7,8]. So far, it has been observed in numerical simulations only (see [9] and, for very recent results, [10,11]). Its theoretical explanation is most elucidating in the framework of high-frequency Floquet theory [4]: the timeaveraged Kramers-Henneberger potential, as it is seen by a free electron moving in the laser field, provides bound states.…”

“…Ionization rates and energy shifts were obtained numerically by Floquet theory [13] or approximate, analytical high-frequency Floquet theory [2,4]. Full numerical ab initio solutions of the timedependent, single-electron Schrödinger equation were obtained for low-dimensional model systems (see, e.g., [14,15,16,17,18,19]) and, after the early work in [9] very recently, in three spatial dimensions for linear polarization [10] and circularly polarized laser pulses [11]. Although the Floquet ionization rates decrease monotonically for laser intensity I → ∞ the ionization probability in full ab initio solutions of the TDSE for finite laser pulses assumes a minimum and increases again thereafter.…”

Factorization of laser–pulse ionization probabilities in the multiphotonic regime

“…To analyse the spectra obtained in DipA we study the different factors in (11). As we mentioned before, L (1) is the ionisation transition matrix due to the absorption of one fictitious photon with frequency ω f i = E f − E i .…”

Computational Investigation of the Interaction Between Hydrogen Atoms and an Intense Circularly Polarized Laser Field

“…In the late 1980s, the Floquet theory was used in those studies [33][34][35]. In recent years, some theoretical physicists have directly solved two-dimension (2D) and three-dimension (3D) cases of the time-dependent Schrodinger equation (TDSE) of hydrogen atoms in an intense circularly polarized laser field [36][37][38][39]. We have focused on this study for more than a decade as well.…”