Carrier-envelope-phase effects in one- and two-photon directional photoionization of nonisotropic atomic states

We study the impact of two-color (ω and 2ω) co- and counterrotating ultrashort attosecond laser pulses on nonisotropic atomic targets through the one- and two-photon interference pattern of the photoelectron spectrum. Specifically, we take the ground state of atomic carbon, i.e., (1s²2s²2p2,³P e ) as a prototype. We observe and quantify the strong dependence on the relative carrier-envelope phase (CEP) of the two-color pulses and on the spatial orientation of the electronic target states. Notably, we observe that the photoelectron momentum distributions (PMDs) vary as a function of the CEP due to the interfering two-color one- and two-photon ionization paths. In addition, the PMD region corresponding to one-photon photoionization remains unaffected with varying CEP, depending only on the ellipticity of the pulse, the central photon frequency, and the magnetic quantum number of the initial state. Therefore, comparing the one-photon ionization electron ejection direction following the absorption of a single (2ω) photon with that of the two-photon ionization channel following the absorption of two photons, each with energy ω, we may extract information on the CEP difference between the two pulses.