Symmetry analysis of the photoelectron continuum in two-photon XUV + IR ionization

The photoelectron momentum distribution (PMD) in two-photon XUV-IR ionization of Ne is studied theoretically by numerical solution of the time-dependent Schrödinger equation and within the analytical soft photon approximation. The symmetry of the PMD, projected on the plane encompassing the joint XUV-IR linear polarization axis, reveals the angular momentum composition of the photoelectron wave packet. This composition, in turn, allows to examine the validity of the angular momentum propensity rules which govern the bound-continuum and continuum-continuum photon driven transitions. The Fano propensity rule for bound-continuum transitions that favors an increase in the angular momentum is confirmed. However, its extension to continuum-continuum transitions suggested by Busto [Phys. Rev. Lett. 123, 133201 (2019)PRLTAO0031-900710.1103/PhysRevLett.123.133201] is less straightforward. In addition, we break the time-reversal symmetry of the XUV field by combining the odd and even multiples of the fundamental frequency. By doing so, we change the time and angular structure of the photoelectron continuum.