Complete characterization of sub-Coulomb-barrier tunnelling with phase-of-phase attoclock

Laser-induced electron tunnelling—which triggers a broad range of ultrafast phenomena such as the generation attosecond light pulses, photoelectron diffraction and holography—has laid foundation for strong-field physics science. Using attoclock constructed by single-colour elliptically polarized laser fields, previous experiments have measured tunnelling rates, exit positions, velocities delay times some specific trajectories, which are mostly created at field peak instant, that is, when electric formed potential barrier stationary in terms derivative versus time. From view wave-particle dualism, phase under classically forbidden, has not been measured, is heart quantum physics. Here we present robust measurement dynamics including sub-barrier amplitude. We combine technique with two-colour phase-of-phase (POP) spectroscopy to accurately calibrate angular streaking relation probe non-stationary manipulating rapidly changing barrier. This POP directly links relative ionization instant any final momentum on detector, allowing us reconstruct imaginary time accumulated The provides general time-resolved approach accessing underlying intense light–matter interactions. Electron probed spectroscopy. Contrary case static tunnelling, angle-to-time mapping found be angularly uniform.