Fig. 1: Attosecond-scale streaking scheme for measuring the tunneling ionization time.
From: Full experimental determination of tunneling time with attosecond-scale streaking method
a An elliptically polarized 800-nm laser pulse maps the tunneling ionization time to the emission angle of the photoelectron in attoclock configurations. A perturbative SH field polarized along the major axis of the fundamental laser ellipse (z axis) is added to precisely determine the tunneling ionization time of the photoelectron in the momentum distribution relative to the instant of the laser-field maximum (t0 = 0). b The electric field strength |E| for three instants, as indicated in (a), slightly oscillates with the relative phase Φ, revealing different phase delays of ΦE, as indicated by the vertical dashed line. The variation of the electric field strength leads to a slight change of the tunneling barrier width. Due to the pronounced nonlinearity of tunneling ionization, the tunneling current will be strongly modulated by the relative phase
