Figure 1

Scheme of the interaction, showing the involved autoionizing levels of the krypton atom. ${\Omega }_{ge}$ is the Rabi frequency for the coupling between the ground state $\mid g⟩$ and each autoionizing state $\mid e⟩$; as explained in the text, we are working in a perturbative regime and a simple two-state dynamics involving the ground state and a single autoionizing state has to be taken into account. ${\Omega }_{g\omega }$ is the analog for the continuum states $\mid \omega ⟩$. The coupling between the autoionizing state and the continuum, due to an intra-atomic interaction, has been denoted by $T_{e\omega }$. Bottom right: temporal scheme of the pulse pair as treated in the theory, i.e., flat top, duration $\tau$, delay $T$, separation $\overline{t}=T-\tau$.Reuse & Permissions

Figure 2

(Color online) Experimental setup. The ninth harmonic, generated by focusing the phase-locked laser pulse pair produced by the Michelson interferometer in the xenon flow and selected by the xuv monochromator, is focused in the krypton jet in the interaction chamber. The ions ejected in the one-photon ionization process are energy analyzed by a time-of-flight (TOF) spectrometer. A flipping mirror can redirect the harmonic field to the exit slit of the monochromator, where a spectrum of the two-pulse field can be measured and used for the fine alignment of the Michelson interferometer. A phosphor-phototube pair, at the exit of the interaction chamber, monitors the transmitted harmonic field intensity.Reuse & Permissions

Figure 3

Typical ion-mass spectrum. In addition to the krypton ions, the spectrum shows the presence of water (top left inset) and xenon (top right inset) coming from the harmonic generation chamber.Reuse & Permissions

Figure 4

Detail of the fringe pattern in the normalized ion signal (continuous curve) around a delay $\Delta t=160\mathrm{fs}$. A sinusoidal fit (dashed curve) is superimposed. The fringe spacing corresponds to the $0.29\mathrm{fs}$ period of the atomic transition. Experimental points result from summing over 1200 laser pulses and smoothing on a fraction $(\approx 20\%)$ of the fringe period.Reuse & Permissions

Figure 5

Fringe contrast vs pulse delay. The solid curve superimposed to the data points is a theoretical curve, as explained in the text, where atomic parameters are obtained by the synchrotron radiation measurements of Ref. 24. No free parameter has been used in the theoretical curve.Reuse & Permissions

Figure 6

Fringe contrast vs pulse delay, where the solid lines are theoretical curves (as in Fig. 5) obtained for varied values of the Fano parameter with respect to Ref. 24. (a) $q_{6d}$ increased by 20%, (b) $q_{6d}$ decreased by 20%, (c) $q_{8s}$ increased by 20%, and (d) $q_{8s}$ decreased by 20%.Reuse & Permissions