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

TL;DR

This study investigates how carrier-envelope phase differences in two-color ultrashort laser pulses influence photoelectron distributions in atomic carbon, revealing phase-dependent interference effects in one- and two-photon ionization processes.

Contribution

It demonstrates the strong dependence of photoelectron momentum distributions on CEP and target orientation, providing insights into controlling atomic ionization with phase-tuned laser pulses.

Findings

Photoelectron momentum distributions vary with CEP due to interference effects.

One-photon ionization distributions depend only on pulse ellipticity, frequency, and initial state quantum number.

Comparison of single- and two-photon ionization directions can reveal CEP differences.

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.