Ionization of the hydrogen atom by intense ultrashort laser pulses

TL;DR

This study compares quantum mechanical and classical approaches to hydrogen atom ionization under intense ultrashort laser pulses, revealing quantum effects dominate low-energy electron emission while classical physics explains high-energy electrons.

Contribution

It provides a detailed comparison of quantum and classical models for atomic ionization, highlighting the role of Coulomb potential in electron energy distributions.

Findings

Quantum and classical models agree at high electron energies.

Quantum effects significantly influence low-energy electron distributions.

Classical trajectories are less affected by Coulomb potential at high energies.

Abstract

The ionization of atomic hydrogen in intense laser fields is studied theoretically. The calculations were performed applying both quantummechanical and classical approaches. Treating the problem quantummechanically, the time dependent Schr\"odinger equation (TDSE) of our system was first transformed into a pseudo-momentum space and solved in this space iteratively. While neglecting the Coulomb potential during the solution of the TDSE we got the results in the Volkov approximation, in the first order solution we taken into account the Coulomb potential as perturbation. The classical calculations were performed within the framework of the classical trajectory Monte-Carlo (CTMC) method. The double differential ionization probabilities are calculated for different laser pulses and a reasonable agreement was found between the theories. Major differences can be observed in the angular distribution of electrons at low electron energies between classical and the quantummechanical approaches. At high electron energies the differences disappear, which indicates that the generation of low energy electrons is of quantum type, and it is strongly influenced by the Coulomb potential, while the production of high energy electrons is of classical type and it is less influenced by the Coulomb interaction. Our results are also compared with the Coulomb-Volkov (CV) model calculations.