Eur. Phys. J. D (2015) 69: 271
https://doi.org/10.1140/epjd/e2015-60471-2

Regular Article

Sudden perturbation approximations for interaction of atoms with intense ultrashort electromagnetic pulses

Curtin Centre for Computation and Department of Physics, Astronomy and Medical Radiation Sciences, Curtin University, GPO, Box U1987, Perth, WA 6845, Australia

^a e-mail: a.lugovskoy@curtin.edu.au

Received: 14 August 2015
Received in final form: 27 October 2015
Published online: 10 December 2015

Abstract

The response of an atom to the action of a pulse shorter than the Kepler period of the optically-active electron is often treated analytically using the sudden-perturbation approximation (SPA). It relies on the truncation of the evolution operator expansion in a series over the dimensionless parameter ε_sysτ_L, where ε_sys is the system-dependent characteristic energy and τ_L is the pulse duration. We examine the SPA with the use of a basis-based solution of the time-dependent Schrödinger equation (TDSE) for the case of a hydrogen atom interacting with two different types of ultrashort pulses, a half-cycle pulse and a few-cycle pulse. The length-gauge form of the electron-field interaction potential is used. The SPA transition probabilities are shown to deviate slightly but systematically from the correct values for the positive-energy states in the region where the sudden-perturbation condition is violated. It is shown that the SPA expectation value of the electron displacement as a function of time differ qualitatively from what follows from the ab initio TDSE solution. Nevertheless, the SPA is shown to be a good approximation for the description of the expectation value of the electron momentum.