Interplay of electron correlation and intense field dynamics in the double ionization of helium

A nonsequential ionization model based on dynamic electron correlation is used to analyze the intensity dependence of the laser-induced single- and double-ionization yields for He at five different laser frequencies. Predictions of the present theoretical model and the recent experimental results are found to agree remarkably well over the entire intensity range. The presence of the ubiquitous ``knee'' structure at the optical wavelengths and its absence at the ultraviolet wavelength are also reproduced by the theory.