Different rescattering trajectories related to different total electron momenta in nonsequential double ionization

We extend earlier work on two-electron photo-ionization to analyze electron momentum. We provide theoretical evidence distinguishing two categories of e-e trajectory associated with the correlation that develops when an outer electron returns to the nucleus in the presence of a high-intensity optical-wavelength laser field. We use the method of back-analysis to connect these two categories of trajectory with NSDI events having either nearly zero (Z) or substantially non-zero ( NZ) total electron momentum. (C) 2003 Optical Society of America.