Photoelectron low-energy structures for arbitrary ellipticity of a strong laser field

Understanding of subtle features in the photoelectron momentum distribution (PMD) in strong-field ionization is vital for ultrafast imaging. One of such features, low-energy structures (LES) are typically linked to Coulomb effects in linearly polarized laser fields, leaving their formation in elliptically polarized fields unexplored. Here we demonstrate, employing numerical solutions of the time-dependent Schrödinger equation and nonadiabatic classical-trajectory Monte Carlo simulations, that the LES induced by specific recollisions persist at any laser ellipticity, provided the nonadiabatic regime is reached with sufficiently large nonadiabaticity. The significant modification of the recollision picture in the nonadiabatic regime, with so-called anomalous and hybrid slow recollisions, is shown to be behind the LES, inducing extreme nonlinear Coulomb bunching in the phase-space. Three regimes of the interaction are identified via the PMD characteristics. Our findings elucidate fine features of the attosecond electron dynamics in strong-field ionization at extreme conditions and indicate limitations on attosecond imaging.