Computational Study of Double Ionization in Intense Bicircular Fields

Since the discovery of multiphoton, multiply charged ionization 35 years ago, the study of double ionization in intense laser fields has been foundational in the development of strong-field physics. In the rescattering model, the Coulomb potential of the atom is distorted by the laser field, leading to liberation of an electron through tunneling. This electron gains energy from the laser field and is driven back to the ion, where it can help free a second electron via impact ionization. Since this process relies on trajectories that bring the first electron back to the ion, it is most effective with linear polarization, and is reduced significantly with increased ellipticity. But it has been shown that a bicircular laser pulse, generated by combining two colors with counter-rotating circular polarization, can also lead to effective double ionization. We recently investigated the dynamics of these processes with a computational study utilizing a classical ensemble [PRL 116, 143005 (2016)]. Here, we present new results generated with a high-performance computational cluster, uncovering novel patterns in recollision timing, identifying classes of complex trajectories that contribute to double ionization, and demonstrating that rescattering can occur even in co-rotating fields.