Momentum-resolved photoelectron emission from xenon in colinearly polarized two-color laser fields at above-threshold ionization conditions is studied both experimentally and theoretically. We utilize phase-ofthe-phase spectroscopy as recently introduced by Skruszewicz et al., Phys. Rev. Lett. 115, 043001 (2015) to analyze the dependence of the yields on the relative phase ϕ between the fundamental and second harmonic laser fields. The resulting phase-of-phase spectra feature a characteristic checkerboard pattern, which can analytically be described within the strong-field approximation.

Phase-of-the-phase spectroscopy using two-color colinearly polarized laser pulses has been introduced and experimentally applied to strong-field tunneling ionization in S. Skruszewicz et al., Phys. Rev. Lett. 115, 043001 (2015) and recently to multiphoton ionization in M. A. Almajid et al., J. Phys. B: At. Mol. Opt. Phys. 50, 194001 (2017). The idea behind phase-of-the-phase spectroscopy is to study in a systematic way the change in the photoelectron yield as a function of the relative phase between the strong fundamental field component (of carrier frequency ω) and a weak, second color component (e.g., 2ω). The observable of interest is the photoelectron-momentum-dependent phase of the change in the electron yield with respect to the relative phase, hence the name "phase of the phase." In the present paper, phase-of-the-phase spectroscopy is extended to circularly polarized light. With a small, counter-rotating 2ω-component, photoelectron spectra have a three-fold symmetry in the polarization plane. The same is true for the corresponding phase-of-the-phase spectra. However, a peculiar, very sharp phase-flip by π occurs at a certain radial momentum of the photoelectron that is sensitive to both laser parameters and the ionization potential. Results from the numerical solution of the time-dependent Schrödinger equation are compared to those from the strong-field approximation. An analytical expression for the momentum at which the phase-of-the-phase flipping occurs is presented.