Abstract
Using the reconstruction of attosecond beating by interference of two-photon transitions (RABBITT) technique, a nonzero phase difference is observed in the two-photon ionization transition of krypton atoms into the ionization channels $^{2}P_{1/2}$ and $^{2}P_{3/2}$ when an electron is removed from the $4p$ shell. The phase difference is studied for excitation energies ranging from $\ensuremath{\approx}18\phantom{\rule{0.28em}{0ex}}\mathrm{eV}$ up to $\ensuremath{\approx}28\phantom{\rule{0.28em}{0ex}}\mathrm{eV}$. The phase differences are found to depend on the relative directions of linear polarization of the photoionization laser pulses and the pulses inducing the subsequent continuum-continuum transition. The experimental results are compared to phase differences calculated on the basis of dipole matrix elements for photoionization and scattering phases known for krypton from earlier experiments. The results indicate that the RABBITT phase differences do not give an obvious direct access to time-delay differences in the primary photoionization step of the atom.
Published Version
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