  Recent advances in laser technology allow us to follow electronic motion at
its natural time-scale with ultra-fast time resolution, leading the way towards
attosecond physics experiments of extreme precision. In this work, we assess
the use of tailored pumps in order to enhance (or reduce) some given features
of the probe absorption (for example, absorption in the visible range of
otherwise transparent samples). This type of manipulation of the system
response could be helpful for its full characterization, since it would allow
us to visualize transitions that are dark when using unshaped pulses. In order
to investigate these possibilities, we perform first a theoretical analysis of
the non-equilibrium response function in this context, aided by one simple
numerical model of the Hydrogen atom. Then, we proceed to investigate the
feasibility of using time-dependent density-functional theory as a means to
implement, theoretically, this absorption-optimization idea, for more complex
atoms or molecules. We conclude that the proposed idea could in principle be
brought to the laboratory: tailored pump pulses can excite systems into
light-absorbing states. However, we also highlight the severe numerical and
theoretical difficulties posed by the problem: large-scale non-equilibrium
quantum dynamics are cumbersome, even with TDDFT, and the shortcomings of
state-of-the-art TDDFT functionals may still be serious for these
out-of-equilibrium situations.
