Ionization of atomic hydrogen in strong infrared laser fields (original) (raw)
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Ionization of Atoms by Intense Laser Pulses
Annales Henri Poincaré, 2010
The process of ionization of a hydrogen atom by a short infrared laser pulse is studied in the regime of very large pulse intensity, in the dipole approximation. Let A denote the integral of the electric field of the pulse over time at the location of the atomic nucleus. It is shown that, in the limit where |A| → ∞, the ionization probability approaches unity and the electron is ejected into a cone opening in the direction of −A and of arbitrarily small opening angle. Asymptotics of various physical quantities in |A| −1 is studied carefully. Our results are in qualitative agreement with experimental data reported in [1, 2].
Physical Review A
The direct multiphoton ionization (MPI) of hydrogenlike ions by intense, linearly polarized, ultrashort infrared laser pulses is investigated within the framework of the strong field approximation (SFA) for laser peak intensities and angular frequencies where relativistic effects are important. We obtain an expression for the differential MPI probability using the Dirac equation and demonstrate that, for the particular case of light ions, the Dirac spin-unresolved MPI probabilities agree with those obtained using the Klein-Gordon equation as well as the relativistic Schrödinger equation. As an example, the interaction of hydrogenlike neon ions with an intense fourcycle Ti:sapphire laser pulse is considered. We show that, in contrast to the nonrelativistic regime, for ultrashort pulses in the relativistic regime, interference effects do not play a role in determining the main features of the energy-resolved photoelectron spectrum. Moreover, we find that the angle-integrated photoelectron spectrum can be obtained using the well-known nonrelativistic SFA formula, properly adjusted to account for the electron drift along the laser propagation direction.
Precise Calculation of Single and Double Ionization of Hydrogen Molecule in Intense Laser Pulses
2010
A new simulation box setup is introduced for the precise description of the wavepacket evolution of two electronic systems in intense laser pulses. In this box, the regions of the hydrogen molecule H2, and singly and doubly ionized species, H2^+ and H2^{+2}, are well discernible and their time-dependent populations are calculated at different laser field intensities. In addition, some new regions are introduced and characterized as quasi-double ionization and their time-dependencies on the laser field intensity are calculated and analyzed. The adopted simulation box setup is special in that it assures proper evaluation of the second ionization. In this study, the dynamics of the electrons and nuclei of the hydrogen molecule are separated based on the adiabatic approximation. The time-dependent Schrödinger and Newton equations are solved simultaneously for the electrons and the nuclei, respectively. Laser pulses of 390 nm wavelength at four different intensities (i.e., 1 × 1014, 5 × 1014, 1 × 1015, and 5 × 1015 W cm-2) are used in these simulations. Details of the central H2 region are also presented and discussed. This region is divided into four sub-regions related to the ionic state H+H- and covalent (natural) state HH. The effect of the motion of nuclei on the enhanced ionization is discussed. Finally, some different time-dependent properties are calculated, their dependencies on the intensity of the laser pulse are studied, and their correlations with the populations of different regions are analyzed.
Semi-analytical model of hydrogen ionization by strong laser pulse at low field frequencies
Journal of Physics: Conference Series, 2014
We consider the interaction of hydrogen atom with a very intense low frequency laser pulse. The Henneberger-Kramers representation of the time-dependent Schrödinger equation is the most appropriate one for this purpose. It is shown that in the case of very low frequencies, the quantum dispersion of the electron wave packet plays a dominant role in the dynamics of the atom.
Precise description of single and double ionization of hydrogen molecule in intense laser pulses
The Journal of Chemical Physics, 2012
In this paper, a new simulation box is introduced for two electronic systems in intense laser pulses. In this box, the region of hydrogen molecule, single ionization and second ionization are precisely recognized and time dependent of population of these regions are reported. In addition, a new regions is introduced and characterized as quasi-double ionization regions and the time dependent population of these regions are calculated and compared at different intensities. The special character of the simulation box is that it is designed in order that to assure the overall second ionization is taken to account. In this study, the dynamics of the electrons and the nuclei of hydrogen molecule are separated based on the adiabatic approximation. The time dependent Schrödinger and Newton equations are solved simultaneously for the electrons and the nuclei respectively. Four different intensities are used in the simulation; 1 × 10 14 , 5 × 10 14 , 1 × 10 15 and 5 × 10 15 W cm −2 with the 390 nm wavelength for all the intensities. The details of the H 2 region is represented and discussed. This region is divided to four sub-regions related to the ionic state H + H − and covalent (natural) state HH. The effect of the internuclear distance and motion of nuclei on the enhanced ionization is discussed. Finally, some different time dependent properties are calculated and their relations with the characteristics of the laser pulse and the population of different regions are studied.
Ionization of hydrogen targets by short laser pulses
We present a distorted-wave formulation of atomic ionization by short laser pulses based on Coulomb-Volkov states. The method is applied to atomic-hydrogen targets, for different interaction times and frequencies.
Single and double ionization of the hydrogen molecule in an intense few-cycle laser pulse
Laser Physics, 2007
In this paper, we present ab-initio two-electron model calculations of laser-induced single and double ionization of the hydrogen molecule in a linearly polarized laser field with static nuclei located along the polarization axis. Within the model, the center-of-mass motion of the two electrons is restricted along the polarization axis of the field, while the relative electron motion is unrestricted. The results of numerical simulations allow us to identify and characterize the mechanisms leading to single and double ionization in an intense fewcycle laser pulse. The role of the rescattering mechanism on the ionization processes is analyzed in particular.
Ionization of a single hydrogen-like atom by laser pulse of near-atomic strength
2007
The dynamics of high-harmonic generation and atom ionization by a strong and superstrong laser field are studied. In contrast to many earlier works, the present theory does not impose limitations on the laser field's strength. We solve the nonrelativistic problem of a single hydrogen-like atom's ionization from the ground state by a short laser pulse of subatomic, atomic, and superatomic field strength. Within the framework of the proposed method, we investigated the matrix elements of the ionization transition and revealed its substantially nonlinear dependence on the laser field strength. Both ionization and recombination processes are taken into account. The proposed method enables us to take into account the arbitrary order multiphoton ionization processes.
International Journal of Innovation and Applied Studies, 2014
The present work aims at analyzing the dynamics of the photoionization process of a hydrogen atom-modelling a single active electron atom-interacting with intense high-frequency laser pulses. The choice of the numerical approach to be used for solving the time-dependent Schrödinger equation (TDSE) of an atom in a laser field is based on the fact that when the intensity of a femtosecond laser get higher, the electron after it reaches the continuum starts behaving as a free electron oscillating in the laser field, which leads to a strong oscillations in the electronic wave function, and then could affect the stability in numerical solutions of TDSE. Therefore a highly stable numerical methods are required for solving the TDSE of an atomic hydrogen in intense laser pulses, for this reason, we chose to use the three-point finite difference method for the spatial discretization of the wave function and the standard Peaceman-Rachford scheme coupled to an inverse iteration procedure for the function's propagation in time. Once the wave function obtained, a spectral analysis of the ejected electron based on the use of a window operator is performed to calculate the probability of ionization of a hydrogen atom by a high frequency laser field.
Experimental ionization of atomic hydrogen with few-cycle pulses
Optics Letters, 2011
We present the first experimental data on strong-field ionization of atomic hydrogen by few-cycle laser pulses. We obtain quantitative agreement at the 10% level between the data and an ab initio simulation over a wide range of laser intensities and electron energies.