  A photoelectron forced to pass through two atomic energy levels before
receding from the residual ion shows interference fringes in its angular
distribution as manifestation of a two-slit-type interference experiment in
wave-vector space. This scenario was experimentally realized by irradiating a
Rubidium atom by two low-intensity continuous-wave lasers [Pursehouse et al.,
Phys. Rev. Lett. 122, 053204 (2019)]. In a one-photon process the first laser
excites the 5p level while the second uncorrelated photon elevates the excited
population to the continuum. This same continuum state can also be reached when
the second laser excites the 6p state and the first photon then triggers the
ionization. As the two lasers are weak and their relative phases uncorrelated,
the coherence needed for generating the interference stems from the atom
itself. Increasing the intensity or shortening the laser pulses enhances the
probability that two photons from both lasers act at the same time, and hence
the coherence properties of the applied lasers are expected to affect the
interference fringes. Here, this aspect is investigated in detail, and it is
shown how tuning the temporal shapes of the laser pulses allows for tracing the
time-dependence of the interference fringes. We also study the influence of
applying a third laser field with a random amplitude, resulting in a random
fluctuation of one of the ionization amplitudes and discuss how the
interference fringes are affected.
