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

Abstract: We study the impact of two-color ($\omega$ and $2\omega$) co- and counter-rotating ultrashort attosecond laser pulses on non-isotropic 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., $(1s^22s^22p^2,{}^3\text{P}^\text{e})$ as a prototype. We observe and quantify the strong dependency 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. Besides, 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 absorption of a single ($2\omega$) photon with that of the two-photon ionization channel following absorption of two photon each with energy $\omega$ we may extrapolate information on the CEP difference between the two pulses.