Low-order above-threshold ionization in intense few-cycle laser pulses

Abstract

The low-energy end of the spectrum of photoelectrons detached from hydrogenic ions exposed to an intense low-frequency few-cycle pulse is calculated within the strong-field approximation (SFA). The effect on the detached photoelectron of the Coulomb field of the nucleus is taken into account quasiclassically. The results are compared with those of an ab initio solution of the time-dependent Schr\"odinger equation, for the case of an ${\mathrm{He}}^{+}$ ion irradiated by a $400\text{\ensuremath{-}}\mathrm{nm}$ pulse of $1\ifmmode\times\else\texttimes\fi{}{10}^{16}\phantom{\rule{0.3em}{0ex}}\mathrm{W}\phantom{\rule{0.2em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}2}$ peak intensity. Many of the features of the ab initio spectra can be understood within the SFA.