Clocking the intrinsic time of multiphoton ionization in linearly polarized fields

We investigate the subcycle temporal property of multiphoton ionization of Ar atoms in a linearly polarized laser pulse at 400 nm by employing the two-color phase-of-the-phase photoelectron spectroscopy. A perturbative weak 800-nm circularly polarized field is used to clock the intrinsic multiphoton ionization dynamics. The resulting phase-of-the-phase spectrum under this field configuration reveals a prominent angular-dependent feature. We show that the angular-dependent phase-of-the-phase is associated with the phase difference of photoelectron intracycle interference. This enables us to access the complex phase of the photoelectron wave packet of multiphoton ionization. The intrinsic complex ionization time of strong-field approximation has been retrieved for above-threshold ionization.