Mechanism of delayed double ionization in a strong laser field

Nonsequential Double Ionization (NSDI), for linearly polarized strong laser fields, has been successfully explained with the recollision model. In this model, an electron, after being ionized by a strong linearly polarized laser field is hurled back and collides with its parent ion and triggers the ionization of a second electron. The picture for NSDI usually yields little delay between the recollision and the subsequent ionization. Experimental and theoretical results have revealed an alternative route in which there is a substantial delay between the recollision and the subsequent ionization. This mechanism has been coined as Recollision Excitation with Subsequent Ionization (RESI). The recollision model usually attributes a passive role to the secondly ionized (inner) electron. In my talk, I will show that the inner electron's role is very far from being a passive one, waiting for a recollision to ionize [1]. I will show that delayed double ionization stems from the inner electron being promoted to a sticky region. I will identify the mechanism that traps and releases the electron from this region and will show a signature of it as oscillations in relative RESI yields.\\[4pt] [1] Phys.~Rev.~Lett. - {\bf 108}, 063001 (2012); Phys.~Rev.~A - {\bf 85}, 066205 (2012)