Semi-analytical model of hydrogen ionization by strong laser pulse at low field frequencies (original) (raw)
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.
Time evolution of a hydrogen atom in a strong, ultrashort, high-frequency laser pulse
Physical Review A, 1995
We have solved the time-dependent Schrodinger equation for a hydrogen atom, initially in its ground state, subject to a strong, ultrashort laser pulse of high frequency, co= 2.0 a.u. We compare and interpret our results in terms of the time-independent Floquet eigenvalues. Even for an ultrashort pulse of 3 cycles half-width, the Floquet adiabatic picture is a very good approximation. We discuss the physical reasons and also the visible deviations from the single-resonance-state approximation.
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.
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.
Ionization of H − by a strong ultrashort laser pulse
We compare the outcome of two different numerical methods aimed at solving the time-dependent Schrödinger equation associated with the interaction of H − with an ultrashort laser pulse. These methods of spectral and configuration interaction type are based on an expansion of the total wavefunction on eigenstates of H − built as products of either B-spline or complex Sturmian functions. A careful analysis of our results together with a comparison with other existing theoretical data sheds some light on subtle aspects of the theoretical treatments of H − in a strong laser field. A particular emphasis is put on the crucial role played by the density of states in the continua.
Ionization and excitation of the hydrogen atom by an electric pulse
Journal of Physics B: Atomic, Molecular and Optical Physics, 2003
We investigate the excitation and ionization of the hydrogen atom using an electric pulse of both Gaussian and rectangular shape. The timedependent Schrödinger equation is solved numerically using the discrete variable representation. In the regime where the pulse duration corresponds to almost adiabatic evolution of the system, an estimate of the probability for inelastic processes based on advanced adiabatic theory is in good agreement with numerical results.
Ionization of the hydrogen atom by short half-cycle pulses: dependence on the pulse duration
European Physical Journal D, 2010
A theoretical study of the ionization of hydrogen atoms by short external half-cycle pulses (HCPs) as a function of the pulse duration, using different quantum and classical approaches, is presented. Total ionization probability and energy distributions of ejected electrons are calculated in the framework of the singly-distorted Coulomb-Volkov (SDCV) and the doubly-distorted Coulomb-Volkov (DDCV) approximations. We also performed quasiclassical calculations based on a classical trajectory Monte Carlo method which includes the possibility of tunneling (CTMC-T). Quantum and classical results are compared to the numerical solution of the time-dependent Schrödinger equation (TDSE). We find that for high momentum transfers the DDCV shows an improvement compared to the SDCV, especially in the low-energy region of the electron emission spectra, where SDCV fails. In addition, DDCV reproduces successfully the TDSE electron energy distributions at weak momentum transfers. CTMC-T results reveal the importance of tunneling in the ionization process for relative long pulses and strong momentum transfers but fails to overcome the well-known classical suppression observed for weak electric fields.
Physical Review A, 2014
We studied the elementary processes of excitation and ionization of atomic hydrogen in an intense 800-nm pulse with intensity in the 1.0 to 2.5 × 10 14 W/cm 2 range. By analyzing excitation as a continuation of above-threshold ionization (ATI) into the below-threshold negative energy region, we show that modulation of excitation probability and the well-known shift of low-energy ATI peaks vs laser intensity share the same origin. Modulation of excitation probability is a general strong field phenomenon and is shown to be a consequence of channel closing in multiphoton ionization processes. Furthermore, the excited states populated in general have large orbital angular momentum and they are stable against ionization by the intense 800-nm laser-they are the underlying reason for population trapping of atoms and molecules in intense laser fields.
A time-dependent variational approach to multiphoton ionization of H atoms in intense laser fields
Journal of Physics B: Atomic, Molecular and Optical Physics, 1991
We present calculations using a variational method for the time-dependent Schrodinger equation for the study of multiphoton ionization of H atoms in intense laser fields. The trial wavefunction is chosen to be an anisotropic Gaussian wavepacket and the case of linear polarization of the laser field is considered. We repon on ionization rates as a function of laser intensity (in the range 10's-10'6 W cm') and frequency (corresponding to ionization by three or more photons) and momentum-dependent electron spectra. Comparison is made with results obtained when the trial wavefunction is an isotropic Gaussian wavepacket and with large-scale numerical calculations. The present method gives reliable results for non-resonant ionization in the limit of high field intensity as well as in the law-frequency limit. The electron momentum distributions are singly peaked and provide a qualitative picture of the ionization process at high field strengths.