Ramsauer-Townsend Diffraction Oscillations in the Two-Dimensional Momentum Distribution of Laser-Ionized electrons

We analyze the two-dimensional momentum distribution of electrons ionized by few-cycle laser pulses in the transition regime from multiphoton absorption to tunneling by solving the time-dependent Schr\"odinger equation and by a classical-trajectory Monte Carlo simulation with tunneling (CTMC-T). We find a complex two-dimensional interference pattern that resembles ATI rings at higher energies and displays Ramsauer-Townsend diffraction oscillations in the angular distribution near threshold. CTMC-T calculations provide a semiclassical explanation for the dominance of selected partial waves. While the present calculation pertains to hydrogen, we find surprising qualitative agreement with recent experimental data for rare gases [1].