Comparative study of photoelectron momentum distributions from Kr and CO2 near a backward rescattering caustic by carrier-envelope-phase mapping

Abstract

We study carrier-envelope-phase- (CEP-) dependent photoelectron momentum distributions (PEMDs) of Kr atoms and randomly oriented ${\mathrm{CO}}_{2}$ molecules exposed to sub-two-cycle intense infrared fields with linear polarization. The adiabatic theory predicts that, at fixed laser parameters (intensity, pulse duration, and CEP), the PEMDs for targets with equal ionization potentials considered across a backward rescattering caustic have identical shapes and only their absolute values depend on the target. We choose Kr and ${\mathrm{CO}}_{2}$ as targets with almost identical ionization potentials (approximately $14$ eV) to explore this behavior of PEMDs. We find that the measured PEMDs for Kr and ${\mathrm{CO}}_{2}$ have cutoff structures, which are associated with the caustics, with identical decaying profiles. We also reveal that CEP-dependent PEMDs around the cutoff exhibit target dependence, reflecting the differences in the differential cross sections (DCSs) of elastic rescattering and tunneling ionization rates. Furthermore, we extract the DCSs from the measured PEMDs around the cutoffs at different CEPs based on the adiabatic theory. The extracted DCSs agree with ones calculated by using the single-active-electron (SAE) scattering model, which includes all multiple-scattering processes, with orientation averaging for ${\mathrm{CO}}_{2}$. In contrast, the independent-atom model, which only considers single-scattering processes, cannot reproduce the extracted DCSs of ${\mathrm{CO}}_{2}$ at low scattering momenta. This finding indicates that multiple scattering is not negligible in the momentum range of 1.5--2.5 a.u. The extracted DCSs also show interference features assigned to multicenter scattering of O-O and C-O. These results confirm that the signature of electron interference is retained after orientation averaging, indicating that the internuclear distances of the constituent atoms can be retrieved from the CEP-dependent PEMDs for randomly oriented molecules using the SAE model.