Dynamics of double ionization within the three-step model strongly depends on the laser field intensity. The maximum energy (in atomic units) gained by the recolliding electron from the laser field is ∼ ∼ 3.2 U p , where U p = F 2 4 ω ω 2 is the ponderomotive energy, F is the laser field strength, and ω ω is the laser frequency. Even when 3.2 U p is far below ionization potential I p experiments have observed correlated ionization. As opposed to the high- U p regime ( 3.2 U p > I p ) in the low- U p regime ( 3.2 U p < I p ) the assistance of the laser field during the recollision is vital.